AQA Chemistry A level

What is the relative mass and charge on a proton?

Mass 1
charge +1

What is the relative mass and charge on a neutron?

Mass 1
Charge 0

What is the relative mass and charge on an electron?

Mass 1/2000
Charge -1

What is the mass number?

The total number of protons and neutrons in the nucleus of an atom

What is the Atomic (proton) number?

This is the number of protons in the nucleus of an atom and is used to identify an element

What are Ions?

Ion have different numbers of protons and electrons. Negative ions have more electrons than protons and positive ions have fewer electrons than protons.

What are isotopes?

Isotopes of an element are atoms with the same number of protons but different numbers of neutrons

describe Thomson's model of the atom.

Thomson's model of the atom was like a 'plum pudding' with a positively charged pudding (solid sphere) that contained negatively charged particles (electrons).

What was found in Rutherford's gold foil experiment?

When alpha particles were fired at a thin gold sheet, most of them passed straight through with a very small number deflected straight back.

What was Rutherford's new nuclear model for the atom?

A tiny positively charged nucleus at the centre, surrounded by a cloud of negative electrons. Most of the atom is empty space.

What did Bohr's atom model show?

Electrons only exist in fixed orbits and not anywhere in between.
Each Shell has a fixed energy.
When an electron moves between shells, electromagnetic radiation is emitted or absorbed.
Because the energy of the shells is fixed, the radiation will have a fixed energy.

What difference is found between the original Bohr atom model and the refined Bohr model?

Scientists discovered that not all electrons in a shell have the same energy, so it was refined to include sub shell's.

What is relative atomic mass?

The average mass of an atom of an element compared to one twelfth of the mass of an atom of carbon 12.

What is relative isotopic mass?

Relative isotopic mass is the mass of an atom of an isotope of an element on a scale where an atom of Carbon-12 is exactly 12.

Calculating relative atomic mass

relative atomic mass = isotopic masses x percentages/total percentage

What is relative molecular mass?

The average mass of an entity compared to one twelfth of the mass of an atom of carbon 12.

What is the equation used to calculate the number of moles of any substance?

Number of moles = mass(g)/ mass of one mole (mol)

What are the 5 stages in mass spectrometery?

vaporisation, ionisation, acceleration, deflection, and detection

What happens during the vaporisation stage of mass spectrometry?

The sample is turned into a gas using an electrical heater in a vacuum.

What happens during the ionisation stage of mass spectrometry?

An electron gun fires a beam of high energy electrons which bombards the gaseous particles, knocking off electrons leaving a positive ion

What happens during the acceleration stage of mass spectrometry?

The positive ions are attracted by negatively charged plates in an electric field which accelerates the ions and focuses the beam.

What happens during the deflection stage of mass spectrometry?

The fast moving ions pas into a string magnetic field, deflecting the ions into a curved path. The degree of deflection depends on the Mass/charge ratio (m/z). Ions with with a high m/z ratio are deflected the least (they're heavier). The strength of the magnet is gradually increased so that ions with different m/z ratios are deflected towards the detector.

What happens during the detection stage of mass spectrometry?

The positive ions hit an electrically charged plate/ the current produced is then amplified and recorded as a 'peak'. Each peak is a measure of the relative abundance of each ion.

What is the general ionisation equation?

X(g) => X+ = e-

What does a mass spectrum chart show?

Each line represents a different isotope of an element. the height of each peak gives the relative isotopic abundance (the amount of it). For a molecular substance the peak with the greatest m/z ratio corresponds to the Mr.

What are the steps in calculating relative atomic mass?

Step 1: For each peak multiply the relative isotopic abundance by the relative isotopic mass.
Step 2: Add up these totals.
Step 3: Divide by 100

How many orbitals do each-sub shell contain?

s - 1
p - 3
d - 5
f - 7

What are four rules for electronic arrangement notation?

1: Each principle and subsidiary level fills up before the next one
2: When the 3p energy level is full, the 4s level fills before the 3d
3: When an atom or ion has 3d electrons, the 4s is written after the 3d
4: Atoms that have 3d electrons always lose the 4s electrons first while forming ions

What is the first ionisation energy?

The first ionisation energy is the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.

How does nuclear charge affect ioniation energy?

The more protons that are in the nucleus, the more positively charged the nucleus is and the stronger the attraction for the electrons

How does distance from the nucleus affect ionisation energy?

Attraction falls off very rapidly with distance. An electron close to the nucleus will be much more strongly attracted than one further away.

How does shielding affect ionisation energy?

As the number of electrons between the outer electrons and the nucleus increases, the outer electrons feel less attraction towards the nuclear charge. This lessening pull of the nucleus by inner shells of electrons is called shielding.

What is the second ionisation energy?

The second ionisation energy is the energy needed to remove an electron from each ion in 1 mole of gaseous 1+ ions.

What is the trend in ionisation energy down group 2?

First ionisation energy decreases down Group 2. This provided evidence that electron shells really do exist.

What is the trend in ionisation energy across periods?

As you move across a period the general trend is for the ionisation energy to increase, it gets harder to remove an electron. This is because the number of protons is increasing which means a stronger nuclear attraction.
There are small drops between groups 2 and 3 due to sub-shell structure, the electron is in a new sub-shell so further away from nucleus, more electron shielding
There is a drop between groups 5 and 6 due to electron repulsion. the repulsion between two electrons in an orbital means that the electrons are easier to remove from shared orbitals.

What is molar mass?

The mass of one mole of something, the same as relative molecular mass but the units are g mol-1

What is the equation linking the number of moles to concentration and volume?

number of moles = concentration x volume (in dm3)

What is the ideal gas equation?

pV=nRT
p = pressure in pascals
V = Volume in m3
n = number of moles
R = 8.31 the gas constant
T = temperature measured in kelvin

What is a neutralisation reaction?

When an acid reacts with an alkali and a salt and water is produced.

What is an empirical formula?

The empirical formula gives the smallest whole number ratio of atoms in a compound.

What is the molecular formula?

The molecular formula gives the actual numbers of atoms in a molecule.

What is the theoretical yield?

The theoretical yield is the mass of the product that should be formed in a chemical reaction. It assumes no chemicals are 'lost' in the process.

What is percentage yield and what is its formula?

For any reaction the actual mass of the product (actual yield) will be less than the theoretical yield.
percentage yield = actual yield / theoretical yield x 100

What is Atom economy?

Atom economy is a measure of the proportion of reactant atoms that become part of the desired product (rather than by-products) in the balanced chemical equation.

What is the formula for Atom economy?

% atom economy = mass of desired product / total mass of reactants x 100

What is electrostatic attraction?

Electrostatic attraction holds positive and negative ions together - it is very strong.

What is ionic bonding?

Ionic bonding is bonds that have electrostatic attraction. When oppositely charged ions form an ionic bond you get an ionic compound.

What are giant ionic lattices?

A lattice is just a regular structure. Ionic crystals are giant lattices of ions. Different ionic compounds have different shaped structures but they're all still giant lattices.

What is the electrical conductivity of an ionic compound?

Ionic compounds conduct electricity when they're molten or dissolved - but not when they're solid. The ions in a liquid are free to move and carry a charge. In a solid they're in a fixed position by the strong ionic bonds.

What is the melting point for ionic compounds?

Ionic compounds have high melting points. The giant ionic lattices are held together by strong electrostatic forces. It takes lots of energy to overcome these forces, so melting points are very high.

What is the solubility of ionic compounds?

Ionic compounds tend to dissolve in water. Water molecules are polar - part of the molecule has a small negative charge and the other bits have small positive charges. The water molecules pull the ions away from the lattice and cause it to dissolve.

What is a covalent bond?

In covalent bonding, two atoms share electrons, so they've both got full outer shells of electrons. Both the positive nuclei are attracted electrostatically to the shared electrons.

What is the electrical conductivity like in a covalent bond?

Simple covalent compounds don't conduct electricity because there are no free ions to carry the charge.

What is the melting point of a covalent bond?

Simple covalent bonds have low melting points because the weak forces between molecules are easily broken.

What is the solubility of the covalent bonds like?

Some simple covalent compounds dissolve in water depending on how polarised the molecules are

What are giant covalent structures

Giant covalent structures have huge networks of covalently bonded atoms. Carbon often forms this type of structure because they can each form four strong covalent bonds.

What are the properties in Graphite?

Graphite has carbon atoms arranged in sheets of flat hexagons bonded with three bonds each. The fourth outer electron of each carbon is delocalised. The sheets of hexagons are bonded together by Van der Waals forces.
Graphites weak bonds means that the layers can easily slide over one another, used in pencils and lubricants.
It can also conduct electricity due to its delocalised electrons that are free to move along the sheets. It has a very high melting point due to the strong covalent bonds in the hexagon sheets. It is also insoluble.

What are the properties of Diamond?

Diamonds carbon atoms are boned to four other carbon atoms. These are arranged in a tetrahedral shape. Diamond has a very high melting point and is very hard, it cannot conduct electricity due to all of its electrons being held in localised bonds. it can also not dissolve in a solvent.

What is a dative covalent bond?

In dative covalent, also known as co-ordinate bonding, one atom proved both of the shared electron in the bond.

What is a lone pair?

An unshared electron pair in a covalent bond.

What is a charge cloud?

Bonding pairs and lone pairs of electrons exist as charge clouds. A charge cloud is an area where you have a really big chance of finding an electron pair.

What is electron pair repulsion theory?

Electrons are all negatively charged, so the charge clouds will repel each other as much as they can. The shape of the cloud charge affects how much it repels other charges. Lone pair charge clouds repel more than bonding-pair charge clouds.

What is electronegativity?

The ability to attract the bonding electrons in a covalent bond. It is meausred on the Pauling scale. The higher the number the better the ability to attract the bonding electrons.

What is a dipole?

When there is a large difference in electronegativity in a polar bond so there is a large difference in charge between the two atoms caused by a shift in electron density in the bond.

What are Van der Waals forces?

Van der Waals forces cause all atoms and molecules to be attracted to one another. They're caused by temporary dipoles which occur when the moving electrons within a charge cloud are more to one side than the other.
Larger molecules or molecules with a greater surface area have more Van der Waals forces.

What are permanent dipole-dipole forces?

these are the weak electrostatic forces that occur between polar molecules.

What is hydrogen bonding?

Hydrogen bonding is the strongest intermolecular force. it only happens when hydrogen is covalently bonded to fluorine, nitrogen or oxygen because they're very electronegative and can pull the bonding electrons away from the hydrogen.
Substances with hydrogen bonding have higher melting and boiling points because of the extra energy needed to break the hydrogen bonds.

What is metallic bonding?

Metal elements exist as giant metallic lattice structures. The outermost shell of electrons of a metal atom is delocalised, leaving a positive metal ion. The positive metal ions are attracted to the delocalised negative electrons.

How does metallic bonding explain the melting points of metals?

The number of delocalised electrons per atom affects the melting point. The more there are, the stronger the bonding will be and the higher the melting point. The size of the metal ion and the lattice structure also affect the melting point.

How does metallic bonding explain metals ability to be shaped?

As there are no bonds holding specific ions together, the metal ions can slide over one another when the structure is pulled, so metals are malleable and ductile (can be pulled into a wire)

How does metallic bonding explain metals ability to conduct electricity?

The delocalised electrons can pass kinetic energy to each other, making them good thermal conductors.
Metals are good electrical conductors because the delocalised electrons can carry a current.

What is the particle structure in solids liquids and gases?

Solids - Its particles are very close together giving it a high density and making it incompressible. The particles vibrate about s fixed point with no free movement
Liquids - Have a similar density to a solid with free moving particles allowing it to flow
Gas - the particles have a high amount of energy and are much further apart. Particles have free movement with little attraction between them.

What is the trend in atomic radius across a period?

Atomic radius decreases across a period.
As the number of protons increases , the positive charge of the nucleus increases. This means electrons are pulled closer to the nucleus, making the atomic radius smaller. The extra electrons are added to the outer energy level so don't really provide any extra shielding.

What is a molecular formula?

A molecular formula is the actual number of atoms of each element in a molecule,

What is the structural formula?

A structural formula shows the atoms carbon by carbon, with the attached hydrogens and functional groups.

What is the displayed formula?

A displayed formula shows how all the atoms are arranged and all the bonds between them

What is the empirical formula?

An empirical formula is the simplest ratio of whole number atoms of each element in a compound.

What is a homologous series?

A homologous series is a bunch of organic compounds that have the same general formula and similar chemical properties.

What are chain isomers?

Chain isomers are a type of structural isomer. They have different arrangements of the carbon skeleton. Some are straight chains and others are branched in different ways.

What are Positional isomers?

Positional isomers are a type of structural isomer. They have the same skeleton and the same atoms or groups attached but the group of atoms are attached to a different carbon atom.

What are functional group isomers?

Functional group isomers area type of structural isomer. They have the same atoms arranged into different functional groups.

How does fractional distillation work?

The crude oil is vaporised at about 350 degrees Celsius and it rises up through the trays. The largest hydrocarbons don't vapourise at all, because their boiling points are too high. As the crude oil vapour goes up the fractional column, it gets cooler creating a temperature gradient. As the alkanes get bigger their boiling point increases so each fraction condenses at a different temperature. The hydrocarbons with the lowest boiling points don't condense, they're drawn off as gases at the top of the column.

Why do people crack hydrocarbons?

Because the light fractions such as petrol and naptha are in higher demand so have a higher value. In order to meet this demand, the less valuable, heavier hydrocarbons are broken into smaller hydrocarbons (including alkenes).

What is thermal cracking?

Thermal cracking takes place as a high temperature of up to 1000'C and high pressures of up to 70 atm. It produces a lot of alkenes which are used to make valuable products like polymers.

What is catalytic cracking?

Catalytic cracking makes mostly motor fuels and aromatic hydrocarbons. It uses a zeolite catalyst at a slight pressure and a high temperature of 450'C. Using a catalyst cuts costs because a lower temperature and pressure can be used. It also speeds up the rate of reaction.

What is complete combustion?

If you burn (oxidise) alkanes with plenty of oxygen, you get carbon dioxide and water

What is incomplete combustion?

If there's not enough oxygen, hydrocarbons cannot combust incompletely and you get a particulate carbon soot and carbon monoxide gas as well as carbon dioxide.
This is bad because carbon monoxide gas is poisonous.

What are unburnt hydrocarbons.

These are emitted when engines don't burn all of the fuel molecules. These hydrocarbons react with nitrogen oxides in the presence of sunlight to form ground level ozone (O3) which is a major component of smog

What is a catalytic converter?

Catalytic converters can help remove the three main pollutants from vehicle exhausts (nitrogen oxides, unburnt hydrocarbons and carbon monoxide) using transition metals such as rhodium and platinum which convert them into less harmful chemicals.

Hess's Law

The Enthalpy Change for a chemical reaction is independent of the route taken

Bond Dissociation Enthalpy

The Enthalpy Change needed to break 1 mole of a covalent bond with all species in the gaseous state

The energy given out is the same as the amount taken in when the bond is formed

always endothermic, ∆H is positive
∆H = ∑(Bonds Broken) - ∑(Bonds Formed)

Mean Bond Enthalpy

The Enthalpy Change needed to break a bond, averaged over different molecules

Why aren't mean bond enthalpy values very accurate?

they are averaged over a range of compounds

How would a value for ∆Hc, differ if it was measured with a reactant in the gaseous state compared to a reactant in the liquid state

more exothermic and negative, as heat is released when water vapour condenses, so less heat is needed to vapourise water. also molecules have more energy in the gaseous state.

Standard Molar Enthalpy of Formation

The Enthalpy Change when 1 mole of a substance is formed from it's constituent elements under standard conditions. With all reactants and products in their standard states
∆Hc = ∑∆Hf(Products) - ∑∆Hf(Reactants)

Standard Molar Enthalpy of Combustion

The Enthalpy Change when 1 mole of a substance is completely burned in excess oxygen under standard conditions with all reactants and products in their standard states.
∆Hc = ∑∆Hc(Reactants) - ∑∆Hc(Products)

Heat

The total energy of all particles present in a given substance. Heat is dependent on the amount of substance

Temperature

Related to average Kinetic Energy of particles in a system, particles move faster and Kinetic Energy increases so temperature goes up. Temperature is independent of amount of substance.

Equation for Measuring ∆H of a reaction

q = mc∆T
∆H = q/mol

m = g or cm3
c = Jg-K-, is the specific heat capacity, the amount of heat needed to raise the temperature of 1g of a substance by 1 K
q= J

Calorimeter: Errors in method

Heat loss, Incomplete fuel combustion, incomplete heat transfer, evapouration of fuel after weighing, measurements are sometimes not under standard conditions, heat capacity of calorimeter isn't included