Module 3 key information Flashcards
How are elements arranged in the periodic table?
Increasing atomic number
What do elements in the same group have in common?
The same number of outer shell electrons
What do elements of the same period have in common?
Same number of highest energy electron shells
What is periodicity?
Repeating trends in chemical and physical properties
What are group 1 metals called?
Alkali metals
What are group2 metals called?
Alkaline earth metals
What are elements in group 3-12 called?
Transition elements
What are elements in group 15 called?
Prictogens
What are elements in group 16 called?
Chalcogens
What are elements in group 17 called?
Halogens
What are elements in group 18 called?
Noble gasses
What is ionisation energy?
How easily an atom loses electrons to form positive ions
What is the definition of first ionisation energy?
The energy required to remove one electron from each atom in 1 mole of gaseous atoms of an element to form one mole of gaseous +1 ions
How can atomic radius affect ionisation energy?
The greater the distance between the outer electrons and the nucleus the fewer nuclear attraction so a decrease in ionisation energy
How does nuclear charge affect ionisation energy?
More protons= greater attraction between the nucleus and outer electrons, increasing ionisation energy
How does electron shielding effect ionisation energy?
Inner electrons repel outer electrons= shielding effect= reduced the amount of attraction between the nucleus and electrons, decreasing ionisation energy
What is the definition of second ionisation energy?
The energy required to remove one electron from each ion in one mole of gaseous +1 ions of an element to form one mole of gaseous +2 ions
Is the second ionisation energy always greater or less than the first ionisation energy?
Greater
How to identify an element from successive ionisation energies?
Large increase between the 3rd and 4th ionisation energies shows that the fourth electron is being taken closer to the nucleus. This means their is 3 electrons in its outer shell so in group three.
Write an equation for the first ionisation energy of magnesium?
Mg(g)——-Mg+(g) + e-
How does ionisation energy change down a group?
1) electron number increases meaning atomic radius increases. Their is less nuclear attraction decreases so the force of attraction is weaker
2) Addition electron shielding from the inncer electrons shells
3) The nuclear charge increases but this is not enough to outweigh the change in atomic radius
OVERALL IONISATION ENERGY DECREASES
How does ionisation energy change across a period?
1) Proton number increases so there is increased nuclear attraction to the outer electrons
2) The atomic radius decreases due to more attraction
3) No additional shells so electron shielding remains the same
OVERALL IONISATION ENERGY INCREASES
Why does ionisation energies decrease from Be to Boron if they are in the same period? (group 2 and 3)
Another subshell (p) was needed and therefore atomic radius increases. 2p orbital has higher energy level therefore easier to remove
Why does ionisation energy decrease from N and O? (group 5 and 6)
Start of electron pairing (spin paired)of the P shell. Electrol repel each other making it easier to remove an electron
What is the definition of metallic bonding?
Strong electrostatic attraction between cations and delocalised electrons
What are some properties of giant metallic lattices?
1) Electrical conductivity= they have mobile electron carriers as the delocalised electrons can move throughout the structure and carry a current
2) High melting and boiling point= due to strong electrostatic attractions
3) Insoluble= May react with polar solvent but this is not classified as dissolving
4) malleable
5) Ductile= can be stretched
Bonding and structure of elements in period 2…
Li and Be—Giant metallic so have metallic bonding which is very strong
B and C—–Giant covalent
N2, O2, F2 and Ne—-simple molecular structure, weak intermolecular forces between molecules and covalent bonding within the molecules
Does silicon have metallic bonding or covalent bonding?
Giant covalent structure so has covalent bonding
Bonding and structure across period 3…
Na, Mg and Al– Giant metallic structure
Si—–giant covalent
P4, S8, Cl2 and Ar–Simple molecular structure
What is the most reactive mtal in group2?
Barium
Physical properties of group 2 metal…
1) Malleable
2) High melting and boiling points
3) Form colourless or white compounds
4) Electrically conductive
Does the reactivity of group 2 metals increase or decrease down the group?
Increase because the atomic radius increases and there is more electron shielding
So electrons are lost more easily
What type of reaction is with group 2 elements and oxygen?
Redox
How to group 2 metals react with water?
Less reactive metals react with water= metal oxide
More reactive metals= hydroxide
Group 2 metal oxides also react with water to form metal hydroxide only
Are group 2 metals oxidising agents or reducing agents?
Reducing agents as they themselves are oxidised
How does the solubility change down group 2?
The solubility increases down the group as the ionic radius increase and forced of attraction within the lattice decreases.
For hydroxides the increase in solubiliity makes the solution more alkaline that why hydroxide of group 2 metals have high PH’s
Is beryllium oxide is insoluble in water?
Yes
What is the use of Ca(OH)2 used for?
Neutralise soil
What is Mg(OH)2 used for?
Antiacid to treat indigestion
What is calcium carbonate used for?
Lime stone so used in construction
What is the drawback of using calcium carbonate?
React with acid ( acid rain)
Properties of halogens?
Form diatomic molecules
Low melting and boiling points
Why does boiling point of halogens increase down the group?
Increased atomic size = stronger london forces between the molecules requiring more energy to break
What are the colours of the halogens?
Fluorine= yellow Chlorine= Green Bromine= Orange Iodine= Purple as a solid and brown as a liquid
How to tell the difference between iodine and bromine by their colours?
Add cyclohexane as it is a non-polar solvent and like dissolves like
Bromine=Orange
Iodine= violet
Why do halogens become less negative down the group?
Atomic radius increases and electron shielding increases. The ability to gain an electron decreases
Also electronegativity decreases down the group
Which halogen is the best oxidising agent?
Chlorine, less atomic radius, easier reduced.
How can you determine the reactivity of halogens?
Displacement reactions
What is a disproportionation reaction?
When the same element is oxidised and reduced in a redox reaction
What are spectator ions?
Ions that remain unchanged in a reactions
What is the equation for the reaction of chlorine and water?
Cl2 + H20——–HClO + HCl
Why is chlorine added to water?
Chloric acid is formed which dissociates to form chlorate ions which kills bacteria
What oxidation number can chlorine have in a chlorate ion?
+5 or +1
What is the test for chlorine in water?
Add chlorine and water. It will first turn the litmus paper red due to two acids and then because of the bleaching effect it will cause the litmus paper to turn white
What is the way to form household bleach from chlorine?
Dont use water due to the low solubility of chlorine in water
Cl2 + dilute NaOH(aq)————-NaClO + NaCl + H20
THIS IS ANOTHER DISPROPORTIONATION REACTIONS
What are the benefits of using chlorine to purify water?
Increases quality of water by killing bacteria and preventing outbreaks of typhoid or cholera.
This makes sure we have safe drinking water
What are the risks of using chlorine to purify water?
Can also be a respiratory irritant in small concentrations and toxic in large conc.
Chlorine can react with organic hydrocarbons formed from decaying vegetation. This will produce chlorinated hydrocarbons which are suspected of causing cancer.
Also do we get a choice
What is the qualitative tests in order?
TEST FOR ANIONS
1)Carbonate test= Add dilute nitric acid. Bubble any gas produced through limewater and a white precipitate forms if Co2 is present.
( Metal carbonate + nitric acid= Metal nitrate + Co2 + H20
C02 + Calcium hydroxide= Calcium carbonate (s)+ H20)#
2) Sulphate test= Add barium nitrate and if sulphate is present a white precipitate forms
(Ba2+ + SO42-= BaSO4(s))
3) Halide test= Add silver nitrate and if a halide is present, a precipitate is formed
Silver chloride- white precipitate
Silver bromide= cream precipitate
Silver iodide= Yellow precipitate
In order to tell them apart, they have different solubility in ammonia
Silver chloride——soluble in dilute NH3(aq)
Silver bromide——soluble in conc NH3(aq)
Silver iodide= ——–insoluble in conc NH3(aq)
TEST FOR CATIONS
1) Ammonium test
Add NaOH(aq) and heat gently
NH4+ + OH- = NH3(g) + H20
This has a distinctive, pungent smell and ammonia is alkaline so will turn damp litmus paper blue
Why must Qualitative tests be done in that order?
BaCO3 also forms a white precipitate so must do carbonate test to get ride of any carbonate
Silver carbonate and silver sulphate both form white precipitates so halide test must be done last
How to test when you have a mixture of ions?
Add excess nitric acid and wait till there is no bubbling
Filter to remove precipitate after sulphate test
What does system mean in a chemical reaction?
The atoms and bonds involved in a chemical reaction
Is breaking bonds endo or exo?
Endothermic it requires energy
How to work out enthalpy change?
Products - reactants
What is activation energy?
Minimum amount of energy required to start a reaction
What is the Ea on an energy profile?
From reactants to the top of the curve
What are the standard conditions?
100KPa
298K (25degrees)
1moldm-3
What is the enthalpy change of formation?
Enthalpy change that takes place when 1 mole of a compound is formed from its elements at standard conditions
Mg + 1/2 O2————MgO
Elements have no enthalpy change of formation
What is enthalpy change of reaction?
Enthalpy change that accompanies a reaction in the molar quantities shown in the chemical equation under standard condition with all reactants at standard states
Mg + 1/2 O2————MgO
What is enthalpy change of neutralization?
Enthalpy change that accompanies a reaction between an acid and a base to produce 1 mole of water under standard conditions with all reactants at standard states
H+ + OH- ————H20
What is enthalpy change of combustion?
Enthalpy change that takes place when 1 mole of a substance completely reacts with oxygen under standard conditions
MUST START WITH 1 MOLE OF WHATEVER YOU ARE BURNING
C4H10 + (6) 1/2O2————-4CO2 + 5H20
How to calculate enthalpy change experimentally?
Q= M X C X change in T Q=KJ M= grams ( total volume x1) C= specific heat capacity T= temp in Kelvin IF U WANT TO FIND ENERGY PER MOLES , Q/MOLES
What is average bond enthalpy?
The mean energy required to break 1 mole of a specified bond in a gaseous molecule
Energy is required to break bonds so it is always endothermic
Everything must be gas
REACTANT - PRODUCTS
Why the enthalpy calculation done experimentally may not be accurate?
Heat loss to the surrroundings
Non standard conditions
Reaction may not have gone to completion
Incomplete combustion
Why average bond enthalpy can be classified as not accurate?
Average mean of the same bonds across different molecules where as if you use standard enthalpy is for that specific molecule
How to calculate the rate of a reaction?
Change in conc (moldm-3) /time(s)
What are the units for rate?
mol dm-3 s-1
Different ways a reaction can be monitored?
Conc of reactant or products
gas volume of the products
Mass of substances formed
What do particles need to undergo sufficient reaction?
They need to have sufficient energy
correct orientation
What are the factors that affect the rate of a reaction?
temp pressure conc surface area catalyst
How does conc/pressure affect the rate of reaction?
Increasing conc of reactant, increases the number of particles in the same volume, closer together so collide more frequently= increases the rate
How does temperature affect the rate of reaction?
Increasing temp, increases the kinetic energy of particles, more particles have reached the activation energy, many more successful collisions= increases the rate
How to work out initial rate of reaction from a graph?
Draw tangent at 0 and calculate gradient
What is a catalyst?
A substance that increases the rate of reaction without undergoing any permanent change itself.
How does a catalyst work?
Provides an alternative reaction pathway which requires a lower activation energy
More particles have the required activation enthalpy, more successful collisions, increases reaction rate
What is a homogenous catalyst?
Same physical state as the reactants. They usually form an intermediate species before regenerating itself (chlorine radicals )
What is a heterogenous catalyst?
It is a different physical state to the reactants.
Usually solid that provide a surface for the reaction to occur.. Reactants are adsorbed and leave via deadsorption. (iron from the haber process)
Benefits of using a catalyst in the industry?
1) can be very expensive but they lower the Ea by reducing the energy requirements= reduces the demand for fossil fuels which is environmentally beneficial as less CO2 is released
2) reduces energy costs making it more profitable
3) Catalysts increase the rate of reaction
4) Catalytic converters= in vehicles that reduce toxic emissions and prevent build up of photochemical smog
What is activation energy?
The minimum amount of energy required by particles for a reaction to occur.
Important features of Boltzmann distribution
No particles has 0 energy so line starts art origin
There is no maximum energy for particles so the line does not cross X- axis
The energy under the curve= total number of molecules
X-axis= energy
Y-axis=number of molecules with a given energy
How Boltzmann distribution is affected by a catalyst?
Shaded area after Ea increases
How does temp affect Boltzmann distribution?
Lower peak but the area remains the same
What is dynamic equilibrium?
The forward reaction rate = the reverse reaction rate. The conc of reactants and products do not change.
IN A CLOSED SYSTEM ONLY
MUST ALL BE GASSES
What factors affect dynamic equilibrium?
Temp
Pressure
Conc
What is Le Chatelier’s principle?
If a dynamic equilibrium is disturbed by changing the condition, the positions of equilibrium moves to counteract that change
How increasing temp affects the position of equilibrium?
Position of equillibrium shift to the endothermic side
How does increasing pressure affect the position of equilibrium?
ONLY IF THERE ARE UNEQUAL NUMBER OF MOLES ON EACH SIDE
shift equilibrium to the side with the fewest moles of gas
How does increasing conc of reactants affect the position of equillibrium?
The rate of the forward reacdtion increases, equillibrium will shift to the right, to make more products
How to calculate Kc?
conc of [product]/ conc of [reactants]
If Kc is greater than 1 what does that show?
Equillibrium favours the products
If Kc is less than 1 what does that show?
Equillibrium favours the reactants
How to work out Kc?
Ratio of moles
Initial moles
Change in moles
Equillibrium moles
Moles/volume= conc
What factor can affect Kc?
ONLY TEMP
