Paper 3B Part1 Flashcards
Define Enthalpy of reaction ΔrH
enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions, with all reactants and products in their standard states
Define Enthalpy of formation ΔfH
enthalpy change when one mole of compound is formed from its constituent elements under standard conditions
Define Enthalpy of combustion ΔcH
enthalpy change when one mole of substance is burnt completely in excess oxygen under standard conditions
How does ionic bonding work?
- Loss of an electron(s) by an element2. Gain electrons by a second element3. Attraction between positive and negative ions
Na + Cl, ionisation electron addinity and latice equations
Ionisation Energy – Na e- + Na+ +496kJmol-1Electron Affinity – e- + Cl Cl- -349kJmol-1Lattice Enthalpy – Cl- + Na+ NaCl -766kJmol-1
What is electron affinity?
.The enthalpy change when one mole of electron is added to one mole of atoms in the gaseous phase to form one mole of -1 ions
Is repulsion between two electrons exothermic or endothermic, why?
.Repulsion between two negatively charged things requires energy so exothermic
What is lattice enthalpy?
.ΔHlatt is the enthalpy change when 1 mole of ionic substance is formed from its gaseous ions under standard conditions
.The strength of the ionic bond is related to the lattice enthalpy, how?
more exothermic the greater the ionic bonding
Lattice enthalpy can’t be measured, why?
Cannot be measured directly as cannot form one mole of ionic lattice from gaseous ions
What are the factors affecting lattice enthalpy? How?
Charge – .The greater the charge on the ions, the stronger the attraction – therefore, more exothermic lattice enthalpySize – .Smaller ions can pack together more tightly, therefore there is greater attraction and more exothermic lattice enthalpy
Why, when moving down group two, do the temperatures required to break the lattice increase?
.They have decreasing charge densities.Mg2+ is a smaller ion than Ba2+ , so the +2 charge occupies a smaller volume – this means Mg2+ has a higher charge density than Ba2+.Mg2+ can distort the electron clouds within the CO32- ion (called polarisation), this weakens the covalent bonding in the ion and reduces its decomposition temperature
Equation to work out lattice enthalpy from born haber cycle
L.E = FORMATION – sum(ATOM + I.E + E.A)orL.E = FORMATION – sum(REST)
What are Born Haber Cycles used for?
Born Haber cycles can be used to calculate a measure of ionic bond strength based on experimental data
Draw the born haber cycle for NaCl
check notes or google
Draw the born haber cycle for MgCl2
check notes or google
Draw the born haber cycle for CuO
check notes or google
Define enthalpy of solution, with an example
DeltasolutionH is the enthalpy change when one mole of ionic compound is completely dissolved in water under standard conditions.e.g. NaCl(s) Na+(aq) + Cl-(aq)
What is enthalpy of hydration with example
- Delta Hhydration¬ is the enthalpy which takes place when one mole of gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions- Na+(g) + aq Na+(aq)
Why is enthalpy of hydration always exothermic?
These are exothermic as bonds are formed between the ions and water molecules
Factors Affecting Enthalpy of Hydration
Charge – the higher charge on the ion, the greater the attraction for the H2O molecules, therefore a more exothermic hydrationSize – smaller ions have a greater charge density compared to the larger ions, this creates a greater attraction for H2O molecules, therefore a more exothermic hydration
Draw the general cycle of enthalpy of solution, hydration and lattice enthalpy
check notes
Equation that links lattice enthalpy, enthalpy of solution, and enthalpy of hydration
lattice enthalpy + enthalpy of solution = sum of the enthalpy of hydrations
A chemical reaction will proceed when?
A chemical reaction will proceed if the products are energetically more stable than the reactants
What is entropy?
Entropy is a measure of the dispersal of energy in a system, the more disordered a system the greater the dispersal of energy = higher entropywe define entropy as a measure of disorder
What happens to entropy over time?
Entropy must increase over time
When is a system in a state of high entorpy?
When its degree of disorder is high
As order within a system increases, its entropy decreases, why?
This can be explained in terms of probability: disordered states are simply more likely to exist (or emerge) than ordered states.The spontaneous direction of change is from a less probable to a more probable state
What does entropy always do?
The total entropy always increases, and the process is irreversible
What is the unit for entropy
Sin JK^-1mol^-1
Why is S (entropy) alwasy potisive?
All substances process some degree of disorder because particles are always in constant motion
How does the entropy of each state differ?
Solid has lowest entropy, and gas has the highest
Draw a graph of waters change in enthalpy as temperaurer increases
check notes
Systems that are more chaotic have a _____ entropy value
higher
(s) (s) + (g) , what is delta S
+
(g) 2(g) , what is delta S
+
What is delta S?C2H5OH(l) C2H5OH(g)
+
What is delta S?C2H2(g) + 2H¬2(g) C2H6(g)
-
What is delta S?NH4Cl(s) + aq NH4Cl(aq)
+
What is delta S?4Na(s) + O2(g) 2Na2O(s) deltaS
-
Define the standard entropy change
The standard entropy change is the entropy change that accompanies a reaction in the molar quantities expressed in the equation, under standard conditions
Sum for delta S^theta
delta S^theta = sum(S^theta products) – sum(S^theta reactants)
Why are exothermic reactions more preferable in nature?
as the products are more stable than reactantsthe key is not the decrease in energy but the associated increase in entropy of the surroundings.
deltaSsurroundings is proportional to what?
NAME?
deltaSsurroundings =
(-deltaHsystem)/T
deltaStotal =
deltaSsystem + deltaSsurroundings
deltaStotal >
0
What can we learn about the entropy of the sun by the photosynthesis equation?
6CO2(g) + 6H2O(l) UV light C6H12O6(s) + 6O2(g)Negative entropy changeEntropy change in sun must be so positive it outweighs every plant on earth
What is gibbs free energy equation?
deltaG = deltaH – T deltaS < 0
How do you get to gibbs free energy equation?
deltaStotal¬ = deltaSsystem + deltaSsurroundings > 0deltaStotal¬ = deltaSsystem – (deltaHsystem)/T > 0T deltaStotal = T deltaSsystem – deltaHsystem > 0-T deltaStotal = -T deltaSsytem + deltaHsystem < 0deltaG = deltaH – T deltaS < 0
Using deltaG explain when a reaction is and is not feasible
deltaG must be negative (<0) for a reaction to be feasible i.e. proceedIf deltaG is positive (>0) then a reaction is not feasible
What is deltaG at the points of feasibility?
At the point of feasibility, we can say deltaG = 0 (assume that deltaH and deltaS don’t vary with temperature)
At low temperatures what does deltaGsystem equal? why?
- At low temperatures, deltaGsystem = deltaH (-T deltaS becomes negligible) so for a reaction to occur it needs to be exothermic
At high tempertaures deltaGsystem ewuals what? why?
- At high temperatures, deltaGsystem = -T deltaS (deltaH becomes negligible) so for a reaction to occur it needs to have a positive deltaS as – T deltaS needs to be less than 0
Limitations to deltaG equation
just because the value is negative and so feasible it doesn’t mean it occurs, the reaction rate might be incredibly slow or the activation energy too high
General properties of d-block elements
The d-block elements have high melting and boiling points.The d-block elements are good conductors of both electricity and heat.
What elements have been used in coinage for many years?
copper, silver, nickel, and zinc
What element is used extensively in construction and production of tools?
Iron
What element is used for electrical cables and water pipes?
Copper
Titanium has great strength, what are the elements applications?
It has many aerospace and medical applications (for example joint replacement).
Sc orbital configuration
[Ar] 4s2 3d1
Fe orbital configuration
Fe – [Ar] 4s2 3d6
Ni orbital configuration
Ni – [Ar] 4s2 3d8
Zn orbital configuration
Zn – [Ar] 4s2 3d10
Cr orbital configuration
Cr – [Ar] 4s1 3d5
Cu orbital configuration
Cu – [Ar] 4s1 3d10
How do copper and chromium minimize repulsions?
Copper and chromium minimize repulsions by being half full or full, chromium has 4s and 3d orbitals half full, copper has 3d full
Fe2+ orbital configuration
Fe2+ - [Ar] 4s0 3d6
Fe3+ orbital configuration
Fe3+ - [Ar] 4s0 3d5
Cu2+ orbital configuration
Cu2+ - [Ar] 4s0 3d9
Cr3+ orbital configuration
Cr3+ - [Ar] 4s0 3d3
Mn2+ orbital configuration
Mn2+ - [Ar] 4s0 3d5
Mn4+ orbital configuration
Mn4+ - [Ar] 4s0 3d3
Sc3+ orbital configuration
Sc3+ - [Ar] 4s0 3d0
Zn2+ orbital configuration
Zn2+ - [Ar] 4s0 3d10
Define a transition element
A transition element is a d-block element that forms at least one ion with an incomplete d sub-shell.
Which ‘d’ block elements do not fit the transition element definition?
- Scandium and zinc
What are some characteristic properties of transition metals and there compounds, with examples. (not conduction, melting, boiling etc.)
- They form compounds in which the transition element has different oxidative stateso Fe2+ = +2o Fe3+ = +3- They form colored compounds- The elements and their compounds can act as catalystso Fe in Haber processo Ni in hydrogenation of alkenes
A species containing a transition element in its highest oxidation state is often a what?
strong oxidizing agent
What does the observed colour of a solution depend on?
The observed colour of a solution depends on the wavelengths absorbed
Why does copper sulphate solution appear blue?
Copper sulphate solution appears blue because the energy absorbed corresponds to red and yellow wavelengths, wavelengths corresponding to blue light aren’t absorbed.
Draw the exam colour chart
check notes
If the colour we observe is red, what colour has been absorbed?
Cyan
What colour is cu2+
white
What colour is [Cu(H2O)6]2+
blue
Transition metals form complex ions or ?
coordination compounds
WHat do transition metals form when they make complex ions?
ligand forms bonds with the central transition metal ion
Examples of complex ions
[Cr(H2O)6]3+ [CuCl4]2-
What is a ligand?
a molecule or ion that can donate a pair of electrons with the transition metal ion to form a coordinate bond
What does monodentate mean?
Monodentate ‘one tooth’ means each ligand donates just one pair of electrons.
Examples of ligands and how many loan pairs they have
H2O (oxygen has two loan pairs) NH3 (nitrogen has a loan pair) Cl- (chloride has a loan pair)CN- (carbon has a loan pair) OH- (oxygen ha a loan pair)
Draw [Cu(H2O)6]2+
check notes
Describe the structure and bonding in [Cu(H2O)6]2+
- The central ion is Cu2+- The ligands are water moleculeso Each molecule donates a pair of electrons from the O atom to the Cu2+ to form a co-ordinate bond- The co-ordination number is 6o This indicates the number of coordinate bonds to the central metal ion
What is the oxidation of Co in [Co(H2O)5Cl]+
2
How to name complex ions?
- The name gives the metal ions and its oxidation state last, and the name/number of ligands before- Pre-fixes di, tri, tetra, penta, hexa used- Ligands are listed alphabetically, with prefixes not allowed to alter this order
[Cr(H2O)4Cl2]+ name
¬¬Tetraaquadichlorochromium (III) ion
[Co(H2O)5Cl]+ name
Pentaaquamonochlorocobalt (II) ion
If the complex ion is an anion, what do you do?
the suffix ‘-ate’ follows the metal
Name of [Fe(CN)6]4-
Hexacyanoferrate (II) ion
What does cobalt become in an anion complex ion?
cobaltate
What does aluminium become in an anion complex ion?
aluminate
What does chromium become in an anion complex ion?
chromate
What does vanadium become in an anion complex ion?
vanadate
What does copper become in an anion complex ion?
cuprate
What does iron become in an anion complex ion?
ferrate
What does nickel become in an anion complex ion?
nickelate
Define catalyst
a substance that increases the rate of a chemical reaction by providing an alternative reaction pathway of lower activation energy (Ea)
What happens when Al3+, Ca2+, Mg2+ Add NaOH or KOH or NH4OH
white precipitate
Description of solution, observation with NaOH, and equation for Copper Cu2+
Transparent blue Pale blue precipitateInsoluble in excess Cu2+(aq) + 2OH-(aq) Cu(OH)2(s)
Description of solution, observation with NaOH, and equation for Iron(II) Fe2+
Pale green Dark green precipitateTurns brown on contact with airInsoluble in excess Fe2+¬(aq) + 2OH-(aq) Fe(OH)2(s)
Description of solution, observation with NaOH, and equation for Iron(III) Fe3+
Orange/brown Orange/brown precipitateInsoluble in excess Fe3+(aq) + 3OH-(aq) Fe(OH)3(s)
Description of solution, observation with NaOH, and equation for Chromium(III) Cr3+
Violet Grey-green precipitateSoluble in excess giving dark green solution Cr3+ + 3OH-(aq) Cr(OH)3(s)Cr(OH)3(s) + 3OH-(aq) [Cr(OH6]3-(aq)
Description of solution, observation with NaOH, and equation for Manganese(II) Mn2+
Pale pink Off white precipitateRapidly turning brown on contact with airInsoluble in excess Mn2+(aq) + 2OH-(aq) Mn(OH)2(s)
- Cu2+(aq) + 2e- Cu(s)If we increase the concentration of Cu2+ ions then:
- Equilibrium moves to oppose the charge- Electrons are removed from the system- The electrode potential becomes more positive
What shape are four coordinate complex ions usualy? with examples
- Tetrahedral is the most common shape- E.g. [CuCl4]2- and [CoCl4]2-
When not tertrahedral, what shape are 4 coordinate complexes, with examples
- Some 4 co-ordinate complex ions are square planar in shape, with the ligands arranged at the corners of a square- E.g. [Ni(NH3)2Cl2] (cis and trans)
When does a square planar shape take place in complex ions? example
- These occur in complexes with 8-d electrons in the d subshell.- E.g. Pt(II), Pd(II), Au(III)
What is cis platin used in?
- Cancer treatment in testicular cancer and useful for ovarian, head and neck, and lung cancer- Extremely toxic
Why did they change from cisplatin to carboplatin?
- Improved chemical stability relative to cisplatin due to chelation by cyclobutane dicarboxylic acid- Essentially equivalent antitumour activity to cisplatin
WHat is oaplatin used in?
treatment of colorectal cancer
Types of cancer therapy
- Surgery- Radiotherapy- Chemotherapyo Cytotoxico Targeted Anti-endocrine Novel targeted agents- Immuno-therapy- Gene therapy
What is mustard Gas? What came about because of mustard gas?
- Potent vesicant agent that burns eyes, skin and respiratory tractMustard Gas = war gasNitrogen Mustard = anticancer drug
How does cisplatin treat cancer?
- The cisplatin binds to DNA and causes a critical structural change n the DNA – a bend of 45 degrees- This stops cell replication and leads to apoptosis (cell death)
Key points of lactic acid
- 2-hydroxy propanoic acid- Also known as lactic acid- The second carbon is a chiral center- The mirror image is non-superimposableo One is found in sour milko The other is found in anaerobic respiration
What is a fuel cell?
a fuel cell is a device that converts chemical energy into electrical energy, water, and heat through electrochemical reactions.
How ddoes a fuel cell work? Are there many or one usually and why?
• Fuel and air react when they come into contact through a porous membrane (electrolyte) which separates them• This reaction results in a transfer of electrons and ions across the electrolyte from the anode to the cathode• If an external load is attached to this arrangement, a complete circuit is formed and a voltage is generated from the flow of electrical currentThe voltage generated by a single cell is typically rather small (< 1 volt), so many cells are connected in series to create a useful voltage.
Differences between a fuel cell and a battery
Hydrogen Fuel Cell – • Open system• Anode and cathode are gases in contact with a platinum catalyst• Reactants are externally supplied, no recharging requiredGalvanic Cell (Battery) – • Closed system• Anode and cathode are metals• Reactants are internally consumed, need periodic recharging
Differences between a fuel cell and an internal combustion engine
Fuel Cell – • Output is electrical work• Fuel and oxidant react electrochemically• Little to no pollution producedInternal Combustion Engine – • Output is mechanical work• Fuel and oxidant react combustively• Use of fossil fuels can produce significant pollution
Similarities between a fuel cell and in internal combustion engine
• Both use hydrogen-rich fuel• Both use compressed air as the oxidant• Both require cooling
Draw an alkaline fuel cell
check notes
What are the half equations, volatages, cell potential, and overall equation for an alkaline fuel cell?
Half Equations – 2H20 (l) + 2e- H2 (g) + 2 OH- (aq) E = -0.83V½ O2 (g) + 2e- 2 OH- (aq) E = +0.40VCell Potential – = 0.4- -0.83 = 1.23VOverall Equation – H2 + ½ O2 H2O
Why Methanol not Hydrogen?
Some new fuel cells use methanol rather than hydrogen as the fuel because- Liquid methanol is easier to store then hydrogen gas- Methanol can be generated from biomass
Define electrochemical reaction
A reaction involving the transfer of electrons from one chemical substance to another
Define electrode
An electrical terminal that conducts an electric current into or out of a fuel cell (where the electrochemical reaction occurs).
Define electrolyte
A chemical compound that conducts ions from one electrode to the other
What is an electrochemical cell consisted of?
An electrochemical cell consists of 2 electrodes + 1 electrolyte
What is rhe equation for the number of optical isomers
- The number of isomers follows the equation: 2n, where n is the number of chiral centres
Why are optical isomers called such?
The isomers are called optical isomers as they can rotate plane-polarized light (light which only travels in one plane)
WHat makes a 6 co-ordinate compound cis or trans?
The bond angle between the two ligands which are different, e.g. 90’ cis, 180’ trans
What is a bidentate ligand? Example
Bidentate – ‘two tooth’ ligandsMost common is ethane-1, 2-diamine
Draw [Ni(NH2CH2CH2NH2)3]2+
Check notes
Describe and explain EDTA4-
A Hexadentate Ligand- EDTA4- has 6 lone pairs, each of which can form a co-ordinate bond- 1 EDTA ion reacts with 1 metal ion- Ethylenediaminetetraacetic acid (EDTA)
What is ligand substitution?
The addition of another ligand to a solution containing the aqua transition metal ion results in a substitution reaction
What occurs for ligand substitution?
- One or more ligands is exchanged for another- A change in colour of the solution is observed- Sometimes the complex ion changes shape/coordinate number
Colour of [Cu(H2O)6]2+, and its colour with dropwise and excess, ammonia and hydrochloric acid
Complex Ion [Cu(H2O)6]2+Pale blue solution Addition of Ammonia Dropwise: Pale blue precipitation of copper(II) hydroxideExcess: Blue precipitate redissolves, forming a deep blue solutionAddition of Concentrated HClDropwise: Begins to turn greenExcess: Begins to turn yellow
Colour of [Cr(H2O)6]3+, and its colour with dropwise and excess, ammonia
Complex ion [Cr(H2O)6]3+Violet solutionAmmonia Dropwise: Grey/green precipitateExcess: Precipitate redissolves to produce a purple solution
Equation for addition of NaOH to [Cu(H2O)6]2+
[Cu(H2O)6]2+ + 2OH- [Cu(H2O)4(OH)2]2+ + 2H2O
Equation for addition of NH3 to [Cu(H2O)6]2+ in dropwise and excess
[Cu(H2O)6]2+ + 2NH3 [Cu(H2O)4(OH)2]2+ + 2NH4+[Cu(H2O)6]2+ + 4NH3 [Cu(NH3)4(H2O)2]2+ + 4H2O
Equation for addition of HCl to [Cu(H2O)6]2+
[Cu(H2O)6]2+ + 4Cl- [CuCl4]2- + 6H2O
Equation for addition of ammonia to [Cr(H2O)6]3+
[Cr(H2O)6]3+ + 6NH3 [Cr(NH3)6]3+ + 6H2O
What is the stability constant?
Kstab – the equilibrium constant existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution reactionLike KC but for equilibrias including complex ions
Colour of Sc3+
Colourless
Colour of Ti2+
colourless
Colour of Ti3+
lilac
Colour of Ti+4
colourless
Colour of Ti5+
colourless
Colour of V2+
lilac
Colour of V3+
green
Colour of V4+
blue
Colour of V5+
yellow
Colour of Cr2+
blue
Colour of Cr3+
green
Colour of Cr4+
colourless
Colour of Cr5+
colourless
Colour of Cr6+
orange
Colour of Mn2+
pale pink
Colour of Mn+3
colourless
Colour of Mn4+
dark purple
Colour of Mn5+
colourless
Colour of Mn6+
green
Colour of Mn7+
lilac
Colour of Fe2+
pale green
Colour of Fe3+
pale yellow
Colour of Fe4+
colourless
Colour of Fe5+
colourless
Colour of Fe6+
colourless
Colour of Co2+
Pink
Colour of Co3+
green
Colour of Co4+
colourless
Colour of Co5+
colourless
Colour of Ni2+
green
Colour of Ni3+
colorless
Colour of Ni4+
colourless
Colour of Cu1+
colourless
Colour of Cu2+
blue
Colour of Cu3+
colourless
Colour of Zn2+
colourless
[Cu(H2O)6]2+ colour
blue solution
Cu(OH)2 colour
Blue precipitate
[Cu(NH3)4(H2O)2]2+ colour
Deep blue solution
[CuCl4]2- colour
Yellow solution
HCl + Cu2+(aq) reaction colour and why
the complex can look green as the reaction is reversible so both blue and yellow species present
[Fe(H2O)6]2+ colour
pale green solution
Fe(OH)2 colour
Green precipitate, if left in air a reddy brown colour appears (Fe2+ oxidizes to Fe3+)
[Fe(H2O)6]3+ colour
Yellow solution
Fe(OH)3 colour
Reddy brown precipitate
[Mn(H2O)6]2+ colour
Very pale solution
Mn(OH)2 colour
Light brown precipitate which darkens in air
[Cr(H2O)6]3+ colour
Violet solution
Cr(OH)3 colour
Grey/green precipitate
[Cr(OH)6]3- colour
Green solution
[Cr(NH3)6]3+
Purple solution
[Cu(H2O)6]2+ + 4NH3
[Cu(H2O)6]2+ + 4NH3 [Cu(NH3)4(H2O)2]2+ + 4H2OBlue solution Deep blue solution
[Co(H¬2O)6]2+ + 6NH3
[Co(H¬2O)6]2+ + 6NH3 [Co(NH3)6]2+ + 6H2O
[Cu(H2O)6]2+ + 4Cl-
[Cu(H2O)6]2+ + 4Cl- [CuCl4]2- + 6H2OBlue solution Yellow/green solution
[Co(H2O)6]2+ + 4Cl-
[Co(H2O)6]2+ + 4Cl- [CoCl4]2- + 6H2OPink solution Blue solution
Cu2+ + 2OH- Cu(OH)2 colours
Cu2+ + 2OH- Cu(OH)2Blue solution blue precipitate
Mn2+ + 2OH- Mn(OH)2 colours
Mn2+ + 2OH- Mn(OH)2Very pale pink solution pale brown precipitate
Fe2+ + 2OH- Fe(OH)2 COLOURs
Fe2+ + 2OH- Fe(OH)2Green solution green precipitate
Fe3+ + 3OH- Fe(OH)3 colours
Fe3+ + 3OH- Fe(OH)3Yellow/brown solution brown precipitate
Cr3+ + 3OH- Cr(OH)3 colours
Cr3+ + 3OH- Cr(OH)3Green solution green precipitate
[Mn(H2O)6]2+ + 2NH3
[Mn(H2O)6]2+ + 2NH3 Mn(H2O)4(OH)2 + 2NH4+
[Fe(H2O)6]3+ + 3NH3
[Fe(H2O)6]3+ + 3NH3 Mn(H2O)3(OH)3 + 3NH4+
Cr(H2O)3(OH)3 + 3OH-
Cr(H2O)3(OH)3 + 3OH- [Cr(OH)6]3- + 3H2OGreen precipitate green solution
Cr(H2O)3(OH)3 + 3H+
Cr(H2O)3(OH)3 + 3H+ [Cr(H2O)6]3+Green precipitate green solution
Cr(OH)3(H2O)3 + 6NH3
Cr(OH)3(H2O)3 + 6NH3 [Cr(NH3)6]3+ + 3H2O + 3OH-Green precipitate purple solution
Cu(OH)2(H2O)4 + 4NH3
Cu(OH)2(H2O)4 + 4NH3 [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH-Blue precipitate deep blue solution
The relative mass of an electron
1/1836
The relative mass of a proton
1
The relative mass of a neutron
1
Charge of proton
1
Charge of neutron
0
Charge of electron
-1
What is an isotope?
Isotopes are atoms of the same element, with a different number of neutrons (same number of protons/electrons)
In the periodic table, horizontal rows are called …
periods
In the periodic table, vertical collums are called …
groups
How many groups are there?
18
What is group 1?
Alkali metals
What is group 2?
Alkaline Earth Metals
What is groups 3-12/
Transition metals
What is group 15?
Pnictogens
What is group 16?
Chalcogens
What is group 17?
The halogens
What is group 18?
The noble gases
What are metalloids/semi metals? Why do they have that name?
Elements that touch the line between metal and non-metals, they have a combination of properties of metals and non-metals
Define ionisation
when an atom loses an electron from its outer shell.
Define first ionisation
The energy required to remove 1 mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions.
What 3 things can affect ionisation energy?
Shielding, nuclear charge and atomic radius
Define shielding
Shielding is when inner electrons screen the outer electrons from the pull from the nucleus
Define nuclear charge
The positive charge of the nucleus
Define atomic radius
Atomic radius is radius of an atom, we measure atomic radius by measuring the distance between 2 nuclei of touching atoms and halving the distance
Describe and explain the trend of atomic radius size as you go along period 3
There is an increase in nuclear charge as you go along the period. The stronger the nuclear charge the more it can pull the electrons closer to the nucleus. The shielding is the same as you go along the period. The general trend for atomic radius is it decreases as you go along period 3 as the electrons are pulled closer to the nucleus.
Describe and explain the trend of period 3 first ionisation energy
First ionisation energy enthalpy increases across a period, the nuclear charge increases across a period, attraction of electrons to the nucleus increases, atomic radius decreases (so electrons are closer), it takes more energy to remove that first electron.
Why does first ionisation energy dip between magnesium and aluminium?
There is a decease between magnesium and aluminium as magnesium has a full sub-shell stability, as the highest occupied sub-shell is complete (3s). Aluminium has one electron in a higher sub-shell (3p), this one electron is removed more easily as it is further away from the nucleus, and therefore the first ionisation energy is lower than magnesium.
Why does first ionisation energy dip between phosphorus and sulphur?
There is a decrease between phosphorus and sulphur because phosphorus has a half subshell stability, sulphur has one 3p orbital that contains a pair of electrons. These paired electrons repel each other, so one of these electrons is easier to remove therefore sulphur has a lower fist ionisation energy then phosphorus.
Describe and explain the trend in first ionisation energy as you go down group 3
First ionisation energy decreases down a group.This is because more inner shell electrons as you go down the group, so there is shielding of outer electrons, attraction of electrons to the nucleus decreases, atomic radius increases (so electrons are further away).
Where does metallic bonding occur?
Only in metals
Describe and explain the metallic structure
.Giant structure.The atoms are in tightly packed layers, which form a regular lattice structure.Each atom in a solid metal structure has donated its negative electrons from its outer shell forming an ion.The outer electrons become delocalised and create a ‘sea of free electrons’.The positive metal ion (cation) is fixed in a portion maintaining the structure of the metal.The delocalised electrons are mobile and can move through the structure
Define metallic bonding
.Metallic bonding is the strong electrostatic attraction between the metal ions (cations) and the delocalised electrons
Where do metals conduct? Why?
.Most only conduct in solid and liquid states.The delocalised electrons can move freely anywhere with the metal lattice allowing them to conduct electricity
Why do metals have large bp/mp?
.Strong electrostatic attraction between the metal ion and the delocalised electrons.Needs a lot of energy to break
What does the strength of the metal depend on? What does this also affect?
.The strength of metal depends on the charge of the metal ion in the structure (the greater the charge, the greater the number of delocalized electrons, the stronger the attraction, the stronger the bond).This also affects the size of the ion (the smaller the ion, the closer the electrons to the nucleus, the stronger the bond)
Do metals dissolve in solvents?
no
Why are metals good conductors of heat?
.When a metal is heated the delocalised electrons gain kinetic energy and move faster.This movement transfers the gained energy throughout the metal
Why are pure metals soft?
When a metal is hit, the layers of metal ions are able to slide over each other, and so the layers do not shatter
What is an alloy and why are they harder than pure metals?
.An alloy is a mixture of two metals, thereby distorting the layers so they can’t slide over each other and make a harder new metal
diamond structure
.Giant covalent bonding.Forms a lattice.Made of carbon only.Strong covalent bond between each atom.Each carbon is bonded to 4 other carbons
Diamond properties
.Hard – a giant covalent structure and has lots of strong bonds.Doesn’t conduct electricity – no delocalised electrons that can move.High melting point – many strong covalent bonds between atoms , it needs a lot of energy to break
Graphite structure
.Giant covalent bonding.Made of carbon only.Hexagonal structure.Strong covalent bonds between carbon atoms.In parallel layers.Weak intermolecular forces between layers.Each carbon is bonded to 3 other carbons.Delocalised electrons in each layer
Graphite properties
.Soft/slippery – the layers can slide over each other because there are weak forces between the layers.Conduct electricity – delocalised electrons that can move through the whole structure.High melting point – graphite has a giant structure with lots of strong covalent bonds between atoms, it needs lots of energy to break bonds
What is graphene? properties
.One layer of graphite.Highly conductive and strong and flexible
What is a nanotube?
When graphene forms a tube like strutcure
What is a bucky ball?
When carbon forms a cage like structure
What are different physical forms of elements called?
allotropes
On a melting point across a period graph, how can you section the different points?
Metallic bonding, giant covalent structures, covalent molecules
Why does the melting point increase across period 3?
.The charge in the metal ions increase.The number of delocalised electrons increases.So the strength of the metallic bonding increases.Need more energy to break stronger metallic bonds so the melting points and boiling points increase
Is silicon a metal or non-metal?
TRICK QUESTIONIts a metalloid
What is silicons structure like?
It has a giant covalent structure exactly the same as carbon in diamond (each silicon is bonded to four other silicon’s)
Why does silicon have a high melting point?
you have to break lots of string covalent bonds in order to melt it, and this requires a lot of energy to break.
How do phosphorus, sulphur and chlorine exist?
simple molecules, with strong covalent bonds between their atoms.
How does argon exist?
Argon exists as separate atoms (it is monatomic)
Why is Cl, Ar, S8 and P4’s melting points so low?
- When these four substances melt or boil, it is the London forces between the molecules which are broken. These are very weak bonds. So little energy is needed to overcome them.
In what order do the melting points of Cl2, Ar, S8 and P4 decrease? Why?
The strength of the intermolecular forces increases with the number of electrons, so the melting point decreases in this order:S8 > P4 > Cl2 > Ar
What contains enthalpy?
Elements and compounds
What is enthalphy (H)?
the heat that is stored in a chemical system
What is a chemical system?
The system refers to the atoms, molecules and ions making up the chemicals
Enthalpy cannot be measured, what can?
Enthalpy change
What is enthalpy change (ΔH)?
the difference in enthalpy between the products and reactants in a reaction
What happens in an exothermic reaction?
.In an exothermic chemical reaction heat energy is transferred from the system to the surroundings.Any energy loss by the system is balanced by the energy gain by the surroundings.The temperature of the surroundings increases, so we see a temperature increase
What happens in an endothermic reaction?
.In an endothermic chemical reaction heat energy is absorbed from the surroundings into the system.Any energy gain by the system is balanced by the energy loss of the surroundings.The temperature of the surroundings decreases, so we see a temperature decrease
Burning fuel, exo or endo?
Exo
Condensing a vapour, exo or endo?
Exo
Evaporation, exo or endo?
Endo
Neutralising an acid, exo or endo?
Exo
Thermal decomposition of copper carbonate, exo or endo?
Endo
Rapid oxidation of iron, exo or endo?
Endo
Shop bought hand warmers, exo or endo?
Exo
Sports injury cool packs, exo or endo?
Endo
Enthalpy change equation
H(Products) – H(Reactants)
Sign for exothermic reaction
negative
Sign for endothermic reaction
positive
Define activation energy
The minimum amount of energy required to start a reaction by breaking the bonds
Draw an exothermic activation energy graph
Check notes
Draw an endothermic activation energy graph
Check notes
Draw an exothermic enthalpy profile
Check notes
Draw an endothermic enthalpy profile
Check notes
Define Enthalpy change of reaction (ΔHr) with example
the enthalpy change when the reaction occurs in the molar quantities shown in the chemical reactione.g. Zn(s) + Cu2+(aq) Cu(s) + Zn2+(aq)
Define Enthalpy change of formation (ΔHf) with example
the enthalpy change when 1 mole of compound is formed from its elementse.g. C(s) + O2(g) CO2(g)
Define combustion change of reaction (ΔHc) with example
the enthalpy change when 1 mole of substance is burnte.g. CH4(g) + O2(g) CO2(g) + H2O(g)
Define Enthalpy change of neutrilisation (ΔHneut) with example
the enthalpy change when solutions of an acid and an alkali react together under standard conditions to produce 1 mole of water. It is always measured per mole of water formed.e.g. HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
What symbol is used for standard conditions?
ϴ
What conditions are used for enthalpy change values?
Standard conditions:Standard pressure = 100KPaStandard temperature = 298K (25’C)Standard concentration = 1 moldm-3
Two equations for calculating enthalpy changes
q = mcΔTΔH = q/n
What is each part of ΔH = q/n?
q = heat energy (J)n = number of moles (mol)
What is each part of q = mcΔT?
q = heat energy (J)m = mass of substance heated or cooled (g)c = specific heat capacity of water (4.18 Jg-1K-1)ΔT = change in temperature (‘C or K)
What is the final step of calculating enthalpy change equations?
Multiply the answer by the co-efficient of the reagent not in excess
When doing enthalpy change calculations, and you dont have a weight for the solution, what do you use?
The volume of it in cm^3, Cm^3 = g
When doing enthalpy change calculations with an equation and bond energy values, how do you get the final answer after finding the values of either side of the equation?
bonds broken - bonds made(left - right)
Define average bond enthalpy
the average enthalpy change when one mole of gaseous covalent bonds is broken
Why might the calculated average bond enthalpy different from the actual?
.The bond enthalpies used in the calculations are averages from different compounds, the exact bond enthalpy depends on the particular compound in which it is either formed or broken.The bond enthalpies are not determined under standard conditions. Bond enthalpies are determined by molecules in a gaseous state. But at 298K not all compounds are a gas, such as water.
In terms of enthalpy, what is breaking of bonds always? Why?
Always endothermic, as you need to add energy to break bonds
What can average bond enthalpy also be called?
Mean bond enthalpy
Where is average bond enthalpy taken from?
the average is taken over a wide range of compounds containing that type of bond
State the standard conditions
Standard pressure = 100kPa (1 atmosphere)Standard temperature = 298K (25’C)Standard concentration = 1moldm-3Standard states of all substances (carbons is a solid, hydrogen is a gas and water is a liquid)
Define standard enthalpy change of reaction
The enthalpy change for a reaction as shown by the molar quantities in the chemical equationsMeasured under standard conditions
Define standard enthalpy change of combustion
Enthalpy change when 1 mole of a substance reacts completely with oxygen under standard conditions`
Define standard enthalpy change of formation
The enthalpy change when 1 moles of substance is formed from its elements under standard conditions
Enthalpy change of formation of elements is always …
zero
What to remember for Hess’ Law Cycles Involving Enthalpies of Formation
Using delta H f it’s p-r!
Formula for hess’ law cycles involving enthalpies of formation
sum of ΔHf products - sum of ΔHf reactants
Why does oxygen have no enthalpy of combustion value?
Oxygen can’t be combusted
What does Hess’ law state?
Hess’ law states that the overall enthalpy change of the two routes is the same
Equation for Hess’ Law Cycles involving enthalpies of combustion
sum of enthalpy of combustion of reactants - sum of enthalpy of combustion of products
Does breaking bonds require or release energy?
Require
Does forming bonds require or release energy?
Release
Define exothermic
the energy required to break bonds is less than the energy given out when new bonds form
Define endothermic
the energy required to break bonds is more than the energy given out when new bonds form
Define average bond enthalpy
the average enthalpy change when one mole of gaseous covalent bonds is broken
Equation for enthalpy change
enthalpy of bonds broken – enthalpy of bonds formed
Why might calculated bond enthalpies not be right?
- The bond enthalpies used in the calculations are averages from different compounds, the exact bond enthalpy depends on the particular compound in which it is either formed or broken2. The bond enthalpies are not determined under standard conditions. Bond enthalpies are determined by molecules in a gaseous state. But at 298K not all compounds are a gas, such as water
Draw a general diagram for Hess’ law
CHECK NOTES
Enthalpy change of reaction –
This is the enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation
Enthalpy change of formation –
This is the enthalpy change when 1 mole of compound is formed from its elements
Enthalpy change of combustion –
This is the enthalpy change when 1 mole of substance is burned
Enthalpy change of neutralisation –
The enthalpy change when solutions of an acid and an alkali react together under standard conditions to produce 1 mole of water. It is always measured per mole of water formed.
Hess’ Law
If a reaction can take place by more than one route, and the initial and final concentrations are the same, the total enthalpy change is the same regardless of the route taken
Things to remember when using Hess’ law
If you have more than one compound, then you have to add the enthalpy of formation for each compound togetherEnthalpy of formation is given for 1 mole of compound formed. If there is more than one mole, you multiply it
What is Hess’ law used for?
Hess’ Law determines enthalpy changes indirectly, for when determining them directly isn’t possible
Where does Hess’ law come from?
Hess’ Law comes from the idea of the conservation of energy
For elements, enthalpy change of formation is ALWAYS ____
zero
Enthalpy change of reaction equation =
sum of the enthalpy change of formation of products - sum of the enthalpy change of formation of reactants OR sum of the enthalpy change of combustion of reactants - sum of the enthalpy change of combustion of products
Definition of Relative Atomic Mass (Ar)
Weighted mean mass of an atom relative to 1/12th the mass of an atom of carbon 12
Definition of Relative Formula Mass (Mr)
The term used when working out the calculation for compounds with giant structures
Name 3 types of giant structures
Giant IonicGiant CovalentGiant Metallic
Definition of Relative Molecular Mass
The term used when working out the calculation for compounds that are simple molecules
Name a type of simple molecular structure
Covalent Compounds
What is the formula for finding out how much of a compound is made up of a particular element?
% of element = ((number of atoms of element x relative atomic mass of the element) / relative formula mass of compound) x 100
What is the molar mass?
.The mass per mol of a substance in g mol^-1.Same number as Mr
What is the amount of substance + unit?
.A means of counting the number of particles in a substance.Unit is the mol
What is Avogadro’s Constant?
(NA) 6.02x10^23 mol-1
What is everything measured relative to?
Carbon-12
Define the mole
The amount of any substance containing as many elementary particles as there are carbon atoms in 12 grams of carbon-12 (6.02x10^23) particles
number of mols (mol) =
mass (g) / molar mass (g mol-1)
Smallest mass of an atom
1.67x10^-27
The largest mass of an atom
4.52x10^-25
What do we use the smallest mass of an atom to do?
Produce a relative scale called the unified atomic mass unit ‘u’ = 1.67x10^-27
If hydrogen-1 = 1u, what does carbon-12 =?
12u
Define relative isotopic mass
The mass of an atom of an isotope relative to 1/12th the mass of a carbon 12 atom
What is 1/12th the mass of a carbon-12 atom?
1u
Define relative atomic mass
The relative atomic mass is the ‘weighted mean’ mass of an atom relative to 1/12th the mass of a carbon-12 atom
formula to find out relative atomic mass/weighted mean?
((mass x abundance) + (mass x abundance)) / 100
Define molecular formula
The number and type of atoms of each element in a molecule
Define empirical formula
Shows the simplest whole number ration of atoms of each element in a compound
State the steps for finding the empirical formula
- find the mass2. calculate the moles3. divide all the results by the smallest value to get the ration4. adjust the ratio to get whole numbers5. workout the empirical formula
What is water of crystallisation?
Water molecules that are bonded into a crystalline structure of a compound
What doe solid compounds formed from aqueous solutions have trapped in their crystal structures?
The crystals that are formed have water molecules trapped in the crystal structure
What does copper sulphate exist as?
Blue crystals
How does copper sulphate lose its water?
Heat
What colour is anhydrous copper sulphate?
White
What is the formula of copper sulphate?
CuSO4.xH2Ox = number of water molecules
Anhydrous definition
Contains no waters of crystillisation
Hydrated definition
A crystallised compound containing water molecules
Where is the water in copper sulphate?
Water forms part of the crystal sturcture
Four steps of the hydrated and anhydrous practical
- Weigh an empty crucible2. Add the hydrated salt into the weighed crucible, weigh the crucible and the hydrated salt3. Using a pipe clay triangle, support the crucible containing the hydrated salt on a tripod. Heat the crucible and contents gently for about one minute. Then heat it strongly for a further three minutes.4. Leave the crucible to cool. Then weigh the crucible and anhydrous salt
What is a binary compound?
Binary compounds contain 2 elements only
How to name a binary compound with one example
To name it, take the first element then change second elements name to –ide (for ionic compounds the metal always comes first) for example magnesium oxide (MgO), sodium chloride (NaCl), Calcium sulphide (CaS)
What is a polyatomic ion?
Ions comprised of more than one atom
What are brackets in formulas used for?
Polyatomic ions need to go into brackets
What is a redox reaction?
When reduction and oxidisation happen at the same time
What is OILRIG
OxidisationIsLossReductionIsGain
What assumptions were made during the copper sulphate anhydrous and hydrated salt experiment? Any extra infomation (how to prevent/any problems that could arise)
.That all the water has been lost – could heat the mass then weigh and repeat till it stays the same to counteract this.No further decompositions – copper oxide might have been made if we heated it too much
When are you allowed to use half values for equation balancing?
In combustion equations, specifically on the oxygen
In what order do you balance combustion equations (hydrocarbons)?
Carbon first then the hydrogen before finally the oxygen
What does aqueous mean?
Dissolved in water
Equipment needed for the determination of the formula for magnesium oxide practical
.access to balance accurate to two decimal places.Crucible and lid.bunsen burner.Tripod stand.heat-proof mat.clay pipe triangle.Tongs
Health and Safety for the determination of the formula for magnesium oxide practical
.Wear eye protection at all time (safety goggles).Take care not to touch any apparatus that is hot.Take particular care at steps 3 and 4, do not look at any bright light given off by the reacting magnesium while it is being heated.Do not place the magnesium ribbon directly in the Bunsen flame
Method for the determination of the formula for magnesium oxide practical
- Measure the mass of crucible and lid2. Put the magnesium ribbon to the crucible. You will need to coil the magnesium so that it fits. Reweigh the crucible and lid.3. Arrange the equipment with a tripod on a heatproof mat, a clay pipe triangle on the tripod, a crucible in the triangle and a bunsen burner under it. Raise the crucible lid slightly using tongs to control the reaction4. When the reaction is nearly complete, place the crucible lid on the heatproof mat and heat the crucible strongly for 5 minutes. During this time, tap the magnesium oxide gently with tongs to break up the residue5. Allow the crucible to cool and reweigh the crucible, its contents, and lid
What is molar gas volume?
The molar gas volume is the volume per mole of gas molecules at the stated temperature and pressure
What are the conditions at RTP?
Conditions: RTP, Room temperature and pressure20’C101KPa (1atm) pressure
At RTP what does 1 mole of gas have a volume of?
24dm^3 (24000cm^3)
What is the volume and molar gas volume equation?
amount n (mol) = Volume V / molar gas volume V
How is a gas a ‘perfect’ or ‘ideal’ gas?
If it obeys the ideal gas equation
When is a gas most close to obeying the ideal gas equation and why?
real gases obey the equation very closely at low pressure (no more than atmospheric pressure) and high temperature (room temperature). Under these conditions a gas is most like a gas and least like a liquid.
What 5 assumptions does the kinetic theory make about gas molecules?
• The particles are moving in straight lines at random.• We can neglect the volume of the particles themselves in comparison with the total volume of the gas (occupy negligible volume).• The particles do not attract one another (exert no force on one another).• The kinetic energy of the particles is proportional to the temperature of the gas.• No energy is lost in collisions between particles.
What is the ideal gas equation?
pV = nRT
In the ideal gas equation what is ‘p’ and what is it measured in?
Pressure, measured in Pa
In the ideal gas equation what is ‘n’ and what is it measured in?
Amount of gas, measured in mol
In the ideal gas equation what is ‘T’ and what is it measured in?
Temperature, measured in K
In the ideal gas equation what is ‘V’ and what is it measured in?
Volume, measured in m^3
In the ideal gas equation what is ‘R’ and what is it measured in?
Ideal gas constant, measured in J/mol/K
What is the ideal gas constant?
8.31 J/mol/K
How to convert from cm^3 to m^3
x10^-6
How to convert from dm^3 to m^3
x10^-3
How to convert from ‘C to K?
273
How to convert from KPa to Pa?
x10^3
Max number of electrons in the first shell?
2
Max number of electrons in the second shell?
8
Max number of electrons in the third shell?
18
Max number of electrons in the fourth shell?
32
What is an electron shell?
A group of atomic orbitals with the same principal quantum number, n
What’s the principal quantum number?
Represented as n, a number representing the overall energy level of the orbital. The bigger the number, the further the distance between the energy level and the atomic nucleus
Formula to work out how many electrons in the shell?
2(n^2)
What is an orbital?
A region of high probability within an atom that can hold 2 electrons with opposite spin
What are shells made up of?
Orbitals
What did Pauli discover in 1924?
.Orbitals only hold 2 electrons.Electrons carry a negative charge.Spin on-axis - generate a magnetic field.Spin clockwise or anti-clockwise, represented by arrows.Electrons in the same orbital must spin in different directions
What does an s-orbital look like?
A sphere
Which shells have s-orbitals?
From n=1 onwards, each shell contains one s-orbital (max two electrons)
What does a p-orbital look like?
Dumbbell shaped, like a balloon squashed in the middle
Which shells have p-orbitals?
From n=2 onwards, each shell contains three p-orbitals (max 6 electrons)
Which shells have d-orbitals?
From n=3 upwards, each shell has 5 d-orbitals (max 10 electrons)
Which shells have f-orbitals?
From n=4 onwards, each shell has 7 f-orbitals (max 14 electrons)
What does each part of the notation 1s^2 represent?
1 = energy levels = type of orbital2 = number of electrons in orbital
What is Aufbau’s principle?
Electrons fill the lowest energy orbitals in sequence
What is the order that the orbitals fill up?
1s 2s 2p 3s 3p 4s 3d 4p 5s
What is an electron energy level made up of?
An electron energy level is made up of atomic orbitals with the same principal quantum number
What is a sub-shell?
Within each shell, orbitals of the same type are grouped together as a sub-shellsEach sub-shell is made up of only one type of orbital only, so there are s, p and d sub-shells
What is Hunds Rule
Electrons singly occupy orbitals before pairing up
When ionising, using the orbital model, which electrons are lost?
The ones in the outer shell, so even if 3d has electrons in it they will be lost from 4s when ionising
Which two elements don’t follow Aufbau’s principle?
Copper and Chromium
How does Copper not follow Aufbau’s principle?
copper steals a 4s electron to gain a full 3d orbitalIt’s actually 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10
How does chromium not follow Aufbau’s principle?
chromium steals a 4s electron to be able to put an electron in every 3d orbitalIt’s actually 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5
How do copper and chromium gain stable structures?
Cr and Cu get stable structures from full and half full 3d sub shells
What do the big numbers in equations show?
The molar ratio
What are atoms trying to achieve when they bond?
A full outer shell
4 key things about ionic bonding
Between metals and non-metalsIts to do with the loss and gain of electronsMetals form positive chargesNon-metals form negative charges
How does an atom gain a positive charge?
It loses electrons, therefore there are more protons than electorns
How does an atom gain a nagative charge?
It gains electrons, therefore there are less protons than electrons
What is an ion?
A charged particle
How do ionic bonds stay together?
The electrostatic attraction between the positive and negative ions
What do you use the crosses and dots for on ionic bonding diagrams?
use crosses for the metals electrons and dots for the non-metals electrons
What is a lattice?
A lattice is a regular repeated three-dimensional arrangement of atoms, ions, or molecules in a metal or other crystalline solution.
What is the structure of ionic compounds like?
A giant ionic lattice, the attraction between the oppositely charged ions acts equally in all directions, which leads to the formation of a giant ionic lattice in three dimensions
Moles equation with concentration and volume
Mol = (cm^3 x moldm^-3) / 1000
Rearrange the moles equation with concentration and volume for concentration =
moldm^-3 = (mol x 1000) / cm^3
What are almost all ionic compounds at room temperature?
solids
Why are almost all ionic compounds solid at room temperature?
At room temperature there is insufficient energy to overcome the strong electrostatic forces of attraction between the oppositely charged ions in the giant ionic lattice, high temperatures are needed to provide this energy
Why is the melting points higher for ionic lattices containing ions with greater ionic charges? What else does ionic attraction depend on?
The melting points are higher for lattices containing ions with greater ionic charges, as there is a stronger attraction between ions.The ionic attraction also depends on the size of the atom
Melting point of NaF
993’C
Melting point of CaF2
1423’C
Melting point of Na2O
1275’C
Melting point of CaO
2614
What do many ionic compounds dissolve in?
Polar solvents like water
Why might an ionic compound not be soluble?
.Polar water molecules break down the lattice and surround each ion in the solution.But in a compound made of ions with large charges, the ionic attraction may be too strong for water to be able to break down the lattice structure, and the compound will then not be soluble
Solubility of NaCL at 20’C
6.1 mol dm^-3
Solubility of CaCl2 at 20’C
0.67 mol dm^-3
Solubility of Na2CO3 at 20’C
2.0 mol dm^-3
Solubility of CaCO3 at 20’C
1.3x10^-4 mol dm^-3
What 2 processes does solubility require?
.The ionic lattice must be broken down.The water molecules must attract and surround the ions
What does the solubility of an ionic compound in water depend on?
on the relative strengths of the attractions within the giant ionic lattice and the attractions between ions and water molecules
As the solubility decreases in ionic compounds…
ionic charge increases
When does and when doesn’t an ionic compound conduct electricity?
.In the solid state, an ionic compound does not conduct electricity.But once melted and dissolved in water the ionic compound does conduct electricity
Describe an ionic compounds electric properties in solid state
.The ions are in a fixed position in the giant ionic lattice.There are no mobile charge carriers, as the ions cannot move.An ionic compound is a non-conductor of electricity in the solid state
Describe an ionic compounds electric properties in a liquid or dissolved state
.The solid ionic lattice breaks down.The ions are now free to move as mobile charge carriers.An ionic compound is a conductor of electricity in liquid and aqueous states
Summarise the properties of ionic compounds
Most ionic compounds – .Have high melting and boiling points.Tend to dissolve in polar solvents such as water.Conduct electricity only in the liquid state or aqueous solutions
What is the main component in teeth, bones and tooth enamel
hydroxyapatite, Ca5(PO4)3OH
What allows tooth decay?
Acid conditions, from food, break down enamel and allow tooth decay
What does saliva do?
Salvia helps to neutralise acidic food and also to replace ions
How do fluoride ions help teeth?
.Fluoride ions help to replace lost ions by forming fluoropatite, Ca5(PO4)3F, which is stronger than hydroxyapatite and more resistant to acid conditions
What do most toothpastes and some water sources contain?
Most toothpastes contain fluoride as sodium fluoride, your water may also contain fluoride depending on where you live
What is the theoretical yield?
The maximum possible amount that can be made
Why is the theoretical yield never achievable?
.The reactions may have not gone to completion.Other reactions (side reactions) may have occurred.Purification of the product may have resulted in loss of product
Percentage yield % =
(actual yield mol / theoretical yield mol) x 100
Describe the use of aqueous barium chloride in qualitative analysis
Test for sulphate ions
What is atom economy?
A measure of the proportion of reactants included in the final useful product
What happens in an ideal reaction, in terms of atom economy?
All reactant atoms end up within the useful product molecule, no waste produced!
What do inefficient reactions have in terms of atom economy?
They are wasteful and have a low atom economy
What do efficient reactions have in terms of atom economy?
.High atom economy.Important for sustainable development.Conserve natural resources and create less waste
What is a bonding pair?
A pair of electrons in a covalent dot n cross diagram that are being used in the reaction
What is a lone pair?
A pair of electrons in a covalent dot n cross diagram that are not being used in the reaction
How is a sigma bond formed?
The head-on overlap of orbitals
In hydrogen what happens in covalent bonding, in terms of orbitals
The two 1s orbitals overlap and they become a molecular orbital
How is the octet rule broken in Boron trifluoride?
It becomes an electron deficient molecule
How can the octet rule be broken in sulphur hexafluoride?
3rd shell of S can hold 18 electrons, octet rule can be broken
What is NH4 ^+
Ammonium ion, a type of molecular ion
What is a dative covalent bond?
A bond formed when both electrons in the share are donated by one atom
For an exam question what should you do?
READ IT ALL AND DO EVERYTHING IT TELLS YOU
Properties of simple covalent molecules
.Low melting and boiling points.Weak intermolecular forces.Not soluble in polar solvents – only in other non-polar liquids.Molecules are not charged so they don’t conduct electricity (no mobile charges).Weak and soft when solid
What does VSEPR theory stand for?
.Valence.Shell.Electron.Pair.Repulsion.Theory
What is the shape of a molecule or ion determined by?
The shape of a molecule or ion is determined by the number of electron pairs in the outer shell of the central atom, more specifically the number of electron pairs repelling as far away from each other as possible (maximum repulsion).
What is the valence shell?
The outer shell
the bond angle of a linear molecule
180’
the bond angle of a triangular planar shape
120’
the bond angle of a tetrahedron
109.5’
the bond angle of an octahedron
90’
Molecular formula of hydrochloric acid
HCl
Molecular formula of sulphuric acid
H2SO4
Molecular formula of nitric acid
HNO3
Molecular formula of ethanoic acid
CH3COOH
Molecular formula of sodium carbonate
Na2CO3
Molecular formula of sodium hydroxide
NaOH
