AS Chemistry Key Notes

• All matter is composed of atoms

• The nucleus is made of protons and neutrons, protons have a relative mass of 1 and a charge of 1+, neutrons have a relative mass of 1 and no charge

• Electrons orbit the nucleus in energy shells, it has a small mass and a charge of -1

• Atoms have no overall charge as they have the same number of protons as electrons.

• The atomic number is equal to the number of protons in the nucleus

• The mass number is equal to the sum of the protons and neutrons in the nucleus

• Isotopes of an element have the same number of protons but different numbers of neutrons.
• In a mass spectrometer, samples are ionised, acelerated to constant kinetic energy, allowed to drift and detected
• Mass spectrometry can be used to find the abundance of isotopes in a sample
• Relative mass is the average mass compared with 1/12 of a carbon atom
• Electrons are arranged in shells with those with the least energy closest to the nucleus
• Each shell consists of subshells called orbitals, there are 4 types s, p, d and f
• The first ionisation energy increases as you go along a period due to the increase in nuclear charge

• Releative molecular mass is the sum of the relative atomic masses of all of the atoms in the molecule
• Relative formula mass is the sum of the atoms that make the formula unit in a compound with a giant structure
• Ideal gas equation: pV=nRT, p = pressure (Pa) V = volume (m3) n = moles (mol) R = 8.31 T = temperature (K)
• The ideal gas equations assumes that particles do not react upon collision, undergo eleastic collisions and there is no intermolecular forces.
• A mole contains 6.02x10^23 particles
• The empiricle formular is the simplest ratio of atoms in a compound
• The molecular formular is the actual ratio
• Concentration is measures in mol dm-3
• Concentration = moles/volume
• A titration can be used tofind the unknown volume or concentration of a reactant.

• An ionic bond is the electrostatic attraction between two oppositely charged ions
• A covalent bond is the electrostatic attraction between the nuclei of the two atoms that share a pair of electrons
• Dative bonds are covalent bonds in which both bonding electrons originate from the same atom
• A metallic bond is the electrostatic attraction between positively charged metal ins and the delocalised electrons
• Crystal structures: Ionic - ions form ionic crystals, Metallic - metallic crystal structure, Macromolecular - non-metals in Group 4 form macromolecular crystals, Molecular - molecules with intermolecular forces can form molecular crystals
• Ionic crystals have high melting points and conduct only when molten
• Metallic crystals have high melting points and conduct electricity
• Macromolecular crystals have high melting points and do not conduct
• moleculat crystal have low melting points and do not conduct
• The shape of a molecule is determined by the bonding and lone pairs of electrons, they arrange themselves to be as far away as possible
• lone pair repulsion is stronger than bonding pair
• Electronnegativity is the stoms ability to draw electron density towards itself in a covalent bond
• Intermolecular forces: permanent dipole-dipole, hydrogen bonds, van der Waals.

• Elements in the periodic table are arranged in order of increasing atomic number
• The periodic table is divided into s, p, d, and f blocks
• Periodicity is used to describe the repaeting protperties in the periodic table
• The atomic radius of elements in Period 3 decreases as the nuclear charge increases
• Across Period 3, the first ionisation energy increases as the nuclear charge increases
• Melting points depend on the bonding and structure of the element

• Organic chemistry is the study of compounds containing carbon
• The structral formular shows the numbers and types of atoms bonded in the molecule in the order of their arrangement
• the displayed formular shows all the atoms used to make a molecule and the bonds between them
• A skeletal formular shows the carbon skeleton and functional groups only
• Carbon compounds with the same functional group and general formular are called homologous series
• The systematic name of an organic molecule with unbranched or branched carbon chains tells you the homologous series to which it belongs, the number of carbon atoms it contains, the position of the functional group and the number and positions of additional functional groups.
• Mechanisms explain how organic reactions happen
• Curly arrows are used to show the movement of electrons

• Structural isomers have the same molecular formulae but different structural formulae
• Chain isomers have the same molecular formulae but different arrangements of carbon an dhydrogen atoms
• Positional isomers have the same molecular formulae but have functional groups on different carbons
• Functional isomers have the same molecular formular but different functional groups
• Stereoisomers have the samemolecular formulae and functional groups but different spatial arrangement of functional groups.

• The hydrocarbons in crude oil can be separated by fractional distillation as they have different bioling points
• Cracking breaks longer alkane molecules into shorter alkanes and alkenes
• Thermal cracking: 450 - 750°C, 70 atm pressure
• Catalytic cracking: 500°C at low pressures, uses zeolites as catalysts
• Thermal cracking provides a higher yield of alkenes
• Catalytic cracking provides a higher yield of branched alkanes
• Alkanes are non-polar and so not very reactive
• They are used as fuels as they react exothermically with oxygen
• Catalytic converters remove carbon monoxide and nitrogen oxides from car exhaust fumes
• Gas flue desulphurisation removes sulphur dioxide from industrial waste gases

• Enthalpy change is the energy transferred during a chemical reaction at a constant pressure
• In exothermic reactions energy is transferred to the surroundings
• In endothermic reactions energy is absorbed from the surroundings
• The standard enthalpy of combustion is the enthalpy change when 1 mole of a substance combusts completely under standard conditions with all reactants and products in their standard states
• The standard enthalpy of formation is the enthalpy change when 1 mole of a substance is formed from its elements with all reactants and products in thei standard states and under standard conditions.
• Calorimetry can be used to determine enthalpy changes, the energy released is used to heat a mass of water and the temperature change is used to calulate the enthalpy change.
• Specific heat capacity is the energy needed to raise the temperature of 1g of a substance by 1K.
• Hess' law states that if a reaction can occur by more than one route then the overall enthalpy change for each route is the same providing the starting anf finishing conditions are the same.
• q=mcΔT
• Bond enthalpy is the enthalpy change when one mole of bonds in gaseous molecules are broken under standard conditions
• Bond enthalpies can be used to calculate enthalpy changes for reactions by considering the total enthalpy change when the bonds were broken and the total when the bonds were made.

• Rate of reaction is affected by the concentration of reactants, temperature and presence of catalysts.
• For a reaction to occur, the reactants must collide with equal to or above the activation energy
• The activation energy is the minimum energy required for a reaction to occur
• The distribution of molecular energies in a gas can be shown using a Maxwell-Boltzmann distribution curve
• An increase in temperature increases the number of particles with equal to or above the activation energy, this increases the rate of reaction
• An increase in concentration increases the rate of reaction as it means that more particles posses above or equal to the activation energy
• Catalysts increase the rate of reaction as they provide an alternate reaction pathway of lower activation energy.

pg 191

• Oxidation = electrons lost
• Reduction = electrons gained
• Oxidising reagents are electron acceptors
• Reducing agents are electron donors
• Oxidation occurs when the oxidation state of an element increases
• Reduction occurs when the oxidation  state of an element decreases
• (group 1 elements have oxidation states of +1, group 7 elements have oxidation states of -1, hydrogen has an oxidation state of +1 and oxygen has an oxidation state of -2)
• Half equations can be used for oxidation and reduction reactions

• Atomic radius increases down Group 2 as the number of electrons increases so does the amount of electron sheilding so the electrostatic attraction betweent he nucleus and electrons is weaker.
• the first ionisation energies decrease as you g down Group 2 as the amount of shell shielding increases the attraction between the nucleus and electron is wekaer so less energy is needed to remove it.
• Melting points decrease down Group 2 as they have smaller charge densities so have weaker metallic bonds
• Group 2 hydroxides: solubility increases down the group, magnesium hydroxide can be used to neutralise stomach acid, calcium hydroxide can be used to neutralise soil
• Group 2 sulphates: solubility decreases down the group, barium sulphate is insoluble so is used in barium meals to line the digestive system
• Acidified barium chloride is used to test for sulphate ions, if they are present a white precipitate (barium sulphate) will appear

• The boiling points increase down Group 7 because of increasing van der Waals forces
• The electronegativity decreases down Group 7 because the atomic radius increases and so the amount of shell sheilding increases meaning that there is a smaller attraction betwen the nucleus and electron
• Halogens are strong oxidising agents as they will readily accept electrons
• The oxidising power decreases down the group
• The reducing power increases down the group
• Acidified silver nitrate is used to test for halide ions
• Aqueous fluoride ions are soluble
• Aqueus chloride ions produce white precipitate (dissolves in dilute ammonia)
• Aqueous bromide ions produce a cream precipitate (dissolves in concentrated ammonia)
• Aqueous iodide ions produce a yellow precipitate (insoluble in concentrated ammonia)
• Chlorine reacts with waer to form chloric acid and hydrochloric acid
• Chloric acid is used to kill bacteria in swimming pools

• Halogenoalkanes are alkanes where one or more hydrogens have been replaced with a halogen
• Carbon - halogen bonds are polar - this makes them vulnerable to attack from nucleophiles
• In nucleophilic substitution an atom is substituted for a halogen atom
• In elimination, a hydrogen and halogen atom are removed to form an alkene
• A nucleophile is an electron pair donor, it has a lone pair of electrons and has a negative charge (apartf from ammonia)
• Nucleophiles are attracted to the carbon in the polar bond
• Halogenoalkanes undergo nucleophilic substitution with OH-, NH3 and CN-
• Halogenoalkanes undergo elimination with OH- ions in ethanolic conditions
• The ozone layer absorbs harmful UV light
• Chlorine radicals were formed when the bond within chlorofluorocarbons were broken by UV light
• The chlorine radicals catalysed a reaction 2O3 → 3O2

• The double bond sin alkenes have high lecton density
• Alkenes can react with hydrogen bromide, sulphuric acid and bromine by electrophilic addition
• An electrophile is an electron pair acceptor
• Addition reactions with unsymmetrical alkenes can give multiple products
• The product is deermined by the most stable intermediate
• Tertiary carbocations are the mos stable, primary carbocations are the leas stable
• Addition polymers are made by the polymerisation of alkenes
• Ethene is polymerised to form poly(ethene)
• Addition polymers are unreactive
• The properties of polymers can be controlled by the reaction conditions used or by addiives

• Alcohols have an OH functional group
• Alcohols are classified as primary, secondary and tertiay depending on the number of carbon atoms bonded to the carbon with the hydroxyl group
• Alcohols can be produced by hydrating alkenes
• Ethanol can be made by reacing ethene with steam using a phosphoric acid catalyst or by fermentation using the enzymes in yeast glucose and water
• Oxidation of a  primary alcohol produces aldehydes, further oxidation can form carboxylic acids. he producs frmed depend on the conditions
• Oxidation of secondary alcohols produces ketones
• Tertiary alcohols do not oxidise easily
• Aldehydes give a positive silver mirror test with Tollen's reagent, kentones do not
• Aldehydes give a brick red precipitate wih Fehling's test, ketones do not

• The test for double carbn carbon bonds is the decolourisation of bromine water
• The halogens in halogenoalkanes can be found using silver nitrate, chorine gives a white precipitate, bromine gives a cream precipitate and iodine gives a yellow precipitate
• Carboxylic acids give a pH lower than 7 (alcohols, aldehydes and ketones are neutral)
• The test for different alcohols, aldehydes andd ketones are the ease of oxidation
• The m/z ratio of a molecular ion is equal to the relaive molcular mass
• High resolution mass spectrometry means that the empirical formular can be worked out
• IR is absorbed by molecules and causes them to vibrate more rapidly
• Different functional group absorb IR of characteristic energy
• The infrared spectrum of a compound can be used to identify a compound