Unit 1: Chemical Change And Structure Flashcards
What is a catalyst?
A substance that increases the rate of a chemical reaction
What happens to a catalyst after a reaction occurs?
It remains the same
Name the two types of catalyst
Biological catalyst and chemical catalyst
Define a chemical and a biological catalyst
A chemical catalyst is elements or substances added to induce a reaction
A biological catalyst is naturally occuring
Define a heterogenous catalyst
It’s a different state from the reactants
Define a homogenous catalyst
It’s in the same state as the reactants
What do catalysts do?
They improve geometry and more successful collisions with lower activation energy
Name the 4 types of bonding amongst the first 20 elements
Metallic
Covalent network
Covalent molecular
Monatomic
Which group have monatomic bonding and what is it?
Group 8 have monatomic bonding and it means they consist of single, unbounded atoms
Name the 7 elements amongst the first 20 have metallic bonding
Lithium
Beryllium
Sodium
Magnesium
Aluminium
Potassium
Calcium
What are covalent networks and what’s their state? (What do covalent networks consist of?
They consist of thousands of atoms joined together with covalent bonds and they are solids
What’s the structure of diamond? (Arrangement)
Tetrahedral arrangement, all four electrons used to make bonds
Whats the structure of graphite? (Arrangement)
3 covalent bonds arranged in hexagonal rings, 4th electron is delocalised in layers
Name 4 of the 20 elements that are diatomic
Nitrogen
Oxygen
Fluorine
Chlorine
What are the diatomic molecules at room temperature? And what’s their size?
Gases and small
What are the diatomic molecules in the first 20 elements examples of?
Covalent molecular molecules
What are the 3 elements in the first 20 that are covalent molecular solids?
Carbon
Phosphorus
Sulphur
What forces do the 3 elements that are covalent molecular solids have? What’s their state at room temperature?
Some weak attraction forces, and can be solid at room temperature
How was the periodic tables invented? (Order)
Invented in order of increasing atomic mass
What does melting point and boiling point depend on?
The strength of forces between the particles
Why are elements on the left of the periodic tables generally stronger?
They have stronger intermolecular forces
What happens to the melting point and boiling point as you go down group 1?
It decreases
What’s the density of a substance? Calculation?
Mass per unit volume, in g/cm3
Define covalent radius
Half the distance between the centres, nuclei, of 2 bonded atoms
Other name for covalent radius?
Atomic size
Here’s covalent radius measured? Unit?
Measured in picometers
What happens as you go across a period?
As we go across a period the nuclear charge and number of outer electrons increases
What happens as you go down a group?
As we go down a group, the number of electron shells or energy levels increases, but the number of outer electrons stays the same
In terms of the trends in atomic size: what happens as you go across a period?
The atomic size decreases as nuclear charge increases and attracts the outer electrons closer to the nucleus
In terms of trends in atomic size: what happens as you go down a group?
As you go down a group the atomic size increases as an extra electron shell is added
Define the term “First ionisation energy”
The amount of energy required to remove one mole of electrons from one mole of atoms in the gaseous state
What does the first ionisation of magnesium look like?
Mg (g) ———> Mg+(g) + e-
Which elements are involved in metallic bonding?
Metals
What happens to first ionisation energy as you go down a group?
It decreases
What happens to the first ionisation energy as you go across a period?
It increases
Define “second ionisation energy”
The amount of energy required to remove one mole of electrons from one mole of gaseous 1+ ions
Show the second ionisation energy formula for magnesium
Mg (g)+ ——> Mg(g) 2+ + e-
Why’s the 2nd ionisation energy of an element always greater than the 1st?
- In the 2nd ionisation energy of negative electrons are being removed from + ions rather than = ones
- in the positive ion there’s a greater attraction for the electron so more energy is needed to remove the 2nd mole of electrons
- successive ionisation energies increases as the atom becomes more positive
- there’s a large jump in ionisation energy when the electron to be removed comes from a new shell, closer to the nucleus
Define electronegativity
It’s a measure of an atoms attraction for the shared pair of electrons in a bond
Trends in terms of electronegativity: what happens across a period?
Electronegativity increases, the charge in the nucleus increases
Trends in terms of electronegativity: what happens down a group?
As we go down a group, electronegativity decreases, atoms have a bigger radius
What is covalent bonding a result of?
What do atoms share?
Two positive nuclei being held together by their common attraction for the shared pair of electrons
Atoms share electrons
What’s ionic bonding and what’s its force of attraction?
It’s the electrostatic force of attraction between the oppositely charged ions
Strong forces of attraction
What type of ions is ionic bonding between? What do ionic compounds form?
It’s between positive and negative ions
Ionic compounds form lattice structures of oppositely charged ions
How do polar covalent bonds form?
What’s it sometimes called?
When distribution of electrons is unequal a polar covalent bond forms (this is sometimes called a dipole)
What is there in polar covalent bonds? (Electronegativity)
There is a difference in electronegativity
What charge does the less electronegative atom develop? Polar covalent bonds
A slightly positive charge and vice versa for the more electronegative atom
Where are electrons pulled in polar covalent bonds?
Closest to the atom with the greatest electronegativity
How does pure covalent bonding occur?
When the elements are the same as one another or the electronegativities are equal or almost equal
What’s the distribution of electrons like in pure covalent bonds?
Bonding electrons are equally shared
What are pure covalent and ionic bonding considered to be on the opposite of?
What lays between?
The bonding continuum, with polar covalent bonding laying between the two extremes
What happens as the difference in electronegativity between two atoms occurs?
The more polar the bond will be, upto 1.9
If the different in electronegativity is 2, what does this mean for the movement of bonding electrons?
The movement of bonding electrons from the element with the lower electronegativity is complete resulting in the formation of ions
What type of bond is it if the difference in electronegativity is 0->0.4?
Pure covalent bonds
What type of bond is it if the difference in electronegativity is 0.5->1.9?
Polar covalent bonds
What type of bonding would it be if the different in electronegativity is 2-»»
Ionic bonding
As a general rule, what’s the electronegativity difference in non polar covalent bonds?
<0.5
As a general rule, what’s the difference of electronegativity in polar covalent bonds?
> 0.5
As a general rule, what’s the difference in electronegativity of ionic bonds?
> 1.7
What’s the melting point of ionic lattices and covalent networks?
High
What’s the melting point of covalent molecular?
Low
What’s the melting point of a metallic lattice?
Can vary, usually high
How do ionic lattices conduct electricity? In which states?
In liquid and dissolved states. Not solid
How do covalent networks conduct electricity? In which states?
They don’t. Only as graphite
How does covalent molecular conduct electricity? In which state?
It doesn’t
How do metallic lattices conduct electricity? In which state?
They conduct in all states
What type of bond is this?
H - Br
2.2 - 2.8
Polar covalent
What type of bond is this?
N —- Cl
3.0 - 3.0
Pure covalent (non polar)
What must you take into consideration when there’s a molecule containing more than two atoms? (Polarity in molecules)
What does the determine?
- all polar bonds within the molecule
- the shape of the molecules
It’s to determine whether it has a permanent dipole ion (an overall polar structure)
Name the two types of covalent molecule (electronegativity)
Polar molecules and non polar molecules
Define polar molecules
Theses are molecules with overall polarity, one end is clearly more negative than the other
Define non polar molecules
These are molecules with no overall polarity
Define a permanent dipole
There is a positive and negative end of the molecule
If a molecule contains polar bonds, what determines whether a molecule has an overall polarity?
Spatial arrangement
If a molecule contains polar bonds, what determines whether a molecule has an overall polarity?
Spatial arrangement
What’s the structure of CO2? Is it polar? Why?
O=C=O
It’s non polar because it’s linear so both ends have a slightly negative charge
Generally are tetrahedral molecules polar or non polar?
Non polar
What are intermolecular forces also known as?
van der waals forces
Where are intermolecular forces present?
Between all molecules
What are the three types of van der waals forces?
1) London dispersion forces (LDFs)
2) Permanent dipole to permanent dipole interaction
3) hydrogen bonding
What break when you melt or boil a substance?
The van der waals forces, NOT the covalent bonds within the molecule
Is it possible for a molecule to have more than one type of van der waals force?
Yes
LDFs: what do electrons do and what does this mean?
Electrons move around atoms randomly which means that more often than not there’s more electrons on one side of the atom than the other
Where do LDFs exist?
Between all atoms and molecules
Why do LDFs arise?
Because electrons move around the atoms
Which molecules are LDFs the main force?
Non- polar molecules
What does the uneven distribution of LDFs cause?
A slightly negative and a slightly positive charge on either side of the atom, known as a temporary dipole
What is an induced dipole and how does it happen? (LDFs)
When another atoms is nearby, the electrons of that atom are repelled by the electron density of the temporary dipole, pushing them to the other side of that atom, creating a second dipole. This is called an induced dipole.
Define an LDF
The forces of attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules
What does the strength of LDFs depend on?
The size of the molecule/atom
What does the strength of LDFs depend on?
The size of the molecule/atom
How are larger dipoles established?
Larger atoms and molecules have more electrons. This leads to larger dipoles being established.
What is a permanent dipole to permanent dipole interaction and how does it occur?
When two polar molecules are near each other there’s an attraction between the negative end of one of the molecules and positive end of the other. This is called a permanent dipole to permanent dipole interaction.
What’s stronger? LDFs or permanent dipole to permanent dipole interaction?
Permanent dipole to permanent dipole interaction
Rank all the van der waals forces by strength
1 = strongest
1 - hydrogen bonds
2- permanent dipole to permanent dipole interaction
3 - London dispersion forces (LDFs)
Where do hydrogen bonds occur? Van der waals forces
Between molecules where there is a very high electronegativity
For a molecule to have hydrogen bonding, it must have one or more of which bonds?
Nitrogen (N-H)
Oxygen (O-H) All highly polar
Fluorine (F-H)
NOF bonding**
Where do permanent dipole to permanent dipole interactions occur?
Between polar molecules
Do polar molecules react to an electric field?
Yes
What would happen if you help a charged rod near a stream of a polar liquid?
The liquid will be attracted or repelled
What is viscosity?
The measure of how thick a liquid is
Do viscous liquids have strong intermolecular forces?
Yes
What is an oxidising agent?
A substance that accepts electrons, whilst being reduced
What does an oxidising agent assist?
Oxidation
Which elements tend to be oxidising agents?
Those with high electronegativities tend to form ions by gaining electrons, so act as oxidising agents
What’s a reducing agent?
A substance that donates electrons, whilst it is oxidised
What does a reducing agent assist?
Reduction
Which elements tend to be reducing agents?
Those which have low electronegativities tend to form ions by losing electrons, so act as reducing agents
Which elements tend to be reducing agents?
Those which have low electronegativities tend to form ions by losing electrons, so act as reducing agents
Which group have the strongest reducing agents?
Group 1
Which group have the strongest oxidising agents?
Group 7
Example of a strong (strongest) reducing agent
Carbon monoxide
Example of oxidising agent
Hydrogen peroxide H2O2
Uses for oxidising agents
They can inactivate viruses and their ideal for bleach due to the oxidation process being an effective means of breaking down coloured compounds
Where are the strongest oxidising agents placed in the electrochemical series?
Bottom left hand column of the electrochemical series
Where are the strongest reducing agents placed in the electrochemical series?
The top of the right hand column
What’s the balanced redox equation for this?
Al(s) ——-> Al3+ (aq) + 3e-
2H+ (aq) + e- ——-> H2 (g)
6H+ + 2AL ——> 2AL3+ + 3H2
What’s always cancelled out in redox equations?
Electrons
What’s miscibility?
The ability for a liquid to “dissolve” another liquid
What aren’t immiscible liquids miscible?
They have a boundary between them
Example: water and hexane
Water is polar, hexane is not
Define solvent
The liquid in which the substance dissolves
What group and one element make covalent network structures?
Group 4 and boron
What is thermochemistry?
The study in changes in heat energy which occur during a chemical reaction
What’s an endothermic reaction?
The reaction takes in heat
What’s an exothermic reaction?
A reaction that releases heat into the atmosphere
Which has higher products energy after a reaction? Endothermic or exothermic
Endothermic because it takes IN heat
What is an activated complex?
An unstable arrangement of atoms formats as react at bonds are broken and product bonds are formed.
When does an activated complex occur?
At the maximum point of the potential energy diagram
What does it mean if an atom has a symmetrical shape? Polarity…
It means there’s no polarity, therefore it’s not permanent
How does sulphur exist?
S8
How does phosphorus exist?
P5
Define the term “nuclear charge”
The force of attraction between the nucleus and outer electrons
Name all the diatomic elements
Chlorine
Hydrogen
Iodine
Nitrogen
Fluorine
Oxygen
Bromine
Alkali metals: what happens as you go down a group?
- Reactivity increases
- melting point and boiling point decreases
Alkali metals: what happens when they react with water? Final product?
React with water to release hydrogen and form hydroxides which dissolve in water making alkaline solutions
Alkali metals: density?
Low density, lithium, sodium and potassium float on water
Transition metals: what do they form and are they catalysts?
They’re catalysts and they form coloured compounds
Transition metals: compared with group 1, melting point, strength, density, reactivity?
Melting point - higher minus per hey
Strength - stronger
Density - harder
Reactivity - less reactive and don’t react as vigorously with water or oxygen
Transition metals: properties (similar/different) etc
Similar properties and some special ones because a lower energy level is being filled in the atoms of elements
Noble gases: 3 features (bonding, reactivity, colour)
Bonding - monatomic
Reactivity - unreactive
Colour - colourless
Halogens: trends down a group? (Mp/bp, reactivity)
Reactivity decreases down the group
Melting point and boiling point increase
Halogens: what two things can they form?
1) ionic salts with metals
2) simple covalent molecules with other non-metals
What happens when you put a more reactive halogen and a less reactive halogen in an aqueous solution?
The more reactive halogen can displace the less reactive one
What’s a fullerene? Bonding
Discrete covalent bond
Covalent networks, strength?
What three elements can form these?
Very strong forces between bonds
3 elements: carbon, boron, silicon
Define a covalent bond
(What creates it?)
When 2 positive nuclei are held together by their common attraction to a shared pair of electrons
Name the 4 factors of reaction rate
Temperature
Concentration
Particle size
Use of a catalyst
Name 5 signs that a chemical reaction has occurred
1 - colour change
2 - smell
3 - change in pH
4 - temperature change
5 - fizzing
What must happen for a reaction to occur?
Particles must collide with a minimum energy to react, called the activation energy
How does pressure affect reaction rate?
Increasing the pressure in a reaction involving gases, reduces the volume for particles to move around in. This results in more collisions, therefore increasing the reaction rate.
Define activation energy
The activation energy, Ea, is the minimum kinetic energy required by colliding particles before a reaction may occur
What affect does a catalyst have on activation energy?
They lower the required activation energy
What is the stored energy that every substance contains called?
Enthalpy
What must happen for a successful collision to take place?
The collision geometry must be correct (the reactant molecules have to be facing the right way! So that the activated complex can be formed
Define metallic bonding
The electrostatic force of attraction between positively charged ions and delocalised electrons
Metal + oxygen —-> ?
Metal oxide
Metal + water ——> ?
Metal hydroxide + hydrogen
Metal + dilute acid ——-> ?
Salt + hydrogen
Name the four states of matter
Liquid. Solid, gas and aqueous
What is an atomic number?
Number of protons
What’s a mass number?
Protons + neutrons
What are atoms made of?
Three subatomic particles
Neutrons, protons and electrons
What’s an isotope?
Atoms with the same atomic number but a different mass number
Name the four structures of molecules
Linear
Angular
Trigon pyramidal
Tetrahedral
An element has the atomic number 11. Using the periodic table you can identify it as?
Sodium
Label this nuclide notation
35
17 Cl
35 —-> mass number
17 —-> atomic number
Cl ——€ symbol
What’s an ionic lattice?
A regular repeating arrangement of metal and non metal ions which creates compounds with very high melting points
The difference between the first ionisation energies of sodium and chlorine is mainly due to the different in?
Number of protons
Explain why electronegativity values decrease going down group 7
Covalent radius increases so attraction of the nucleus for the outer electrons decreases
Explain fully why the boiling points of the halogens increase going down group 7 (3 marks)
It’s because the intermolecular forces increase going down a group
LDFs are forces between the molecules
The more electrons the stronger the LDFs
Explain the decrease in atom size going across the third period from sodium to argon
Increase in the number of protons in the nucleus
Silicon nitride has a melting point of 1900°C and does not conduct electricity when molten
Explain fully, in terms of structure and bonding, why silicon nitride has a high melting point (2 marks)
Silicon nitride is a covalent network.
Strong covalent bonds are broken
Explain fully why, of these three chlorides, silicon tetrachloride is the most soluble in hexane.
Silicon tetrachloride, phosphorus and sulfur (2 marks)
Silicon tetrachloride and hexane are non-polar.
Silicon tetrachloride is non-polar due to its shape cancelling out
The different between the first ionisation energies of sodium and chlorine is mainly due to the difference in the…
Number of protons
Which of the following contains pure covalent bonds?
CO2, H2S, PH3, CF4
PH3
A student is carrying out a titration. Which of the following would help the student to accurately observe the end-point?
1) repeating the titration
2) using a white tile under the flask
3) rinsing the flask between titrations
4) disregarding the rough titre
Using the white tile under the flask
Write the equation for the first ionisation of phosphorus
P(g) ——> P+(g) + e-
Explain why the melting point of phosphorus P5, is much higher than that of nitrogen N2. Refer to the intermolecular forces involved. 3 marks
1) stronger intermolecular forces between phosphorus compared to nitrogen
2) LDFs are the intermolecular forces present
3) There are more electrons in P5 compared to N2
Why does silicon dioxide have a high melting point? (2 marks)
Silicon dioxide is a covalent network
Strong covalent bonds are broken
Explain full why chloromethane has a lower boiling point than water. In your answer you should refer to the intermolecular forces involved
Chloromethane has permanent dipole to permanent dipole interactions whereas water has hydrogen bonding
Hydrogen bonding is stronger than permanent dipole to permanent dipole interactions
Titanium chloride is a liquid at room temperature. Suggest the type of bonding and structure present in titanium chloride
Covalent molecular
Write the ion-electron equation for the oxidation of magnesium atoms
Mg(s) —-> Mg2+ (aq) + 2e-
