all definitions

atomic number

number of protons in the nucleus of an atom

mass number

sum of the number of protons and neutrons in the nucleus of an atom

nuclear charge

total charge of all the protons in the nucleus, has same value as the atomic number

isotopes

atoms of the same element with the same number of protons but a different number of neutrons

relative atomic mass

the average weighted mean mass of an atom relative to 1/12th the mass of carbon-12

relative isotopic mass

the average weighted mean mass of an indiviudal atom of a particular isotope relative to 1/12th the mass of carbon-12

relative molecular mass

the average weighted mean mass of a molecule relative to 1/12th the mass of carbon-12

quantum shells

electron shells that specify the energy level of an electron

first ionisation energy

the energy required to remove one electron from each atom in one mol of atoms in the gaseous state

second ionisation energy

the energy required to remove one electron from each 1+ ion in one mol of 1+ions in the gaseous state

orbital

a region in an atom that can hold upto 2 electrons with opposite spins

periodicity

trends in element properties with increasing atomic number

shielding

a decrease in nuclear charge experienced by an outer shell electron caused by electron-electron repulsion between the outer shell electron and electrons from adjacent quantum shells

ionic bonding

the strong electrostatic attraction between oppositely charge ions

cation

a positively charged ion

anion

a negatively charged ion

isoelectronic species

chemical species that have the same number of electrons so the same electronic configuration

covalent bonding

the strong electrostatic attraction between 2 nuclei and a shared pair of electrons

sigma bond

a bond that results from end-on overlap of 2 orbitals, more stable as there are 2 overlapping regions

pi bond

a bond that results from side-on overlap of 2 orbitals, less stable as there is one overlapping region

dative covalent bond

a covalent bond formed when one atom donates both electrons in a bond

allotropes

different forms of the same element

malleable

a substance that can be shaped

ductile

a substance that can be drawn into a wire

intermolecular forces

forces between molecules

electronegativity

an atom’s ability to attract a pair of electrons in a covalent bond

dipole

difference in charge between the 2 atoms of a covalent bond caused by a shift in electron density in the bond due to the electronegativity difference between elements participating in the bonding

metallic bonding

the strong electrostatic attraction between a positively charged ionic lattice and sea of delocalised electrons

delocalised electrons

electrons that are not contained within a single atom or a covalent bond

london forces

weak intermolecular forces caused by the random movement of electrons resulting in a temporary instantaneous dipole being formed which can induce another dipole on a second molecule

permanent dipole-dipole interactions

dipole-dipole interactions between polar molecules

hydrogen bond

intermolecular force between hydrogen and a more electronegative atom (N,F,O)

oxidation number

the charge of an ion or theoretical charge of an atom in a covalently bonded compound assuming the bond becomes ionic

oxidation

loss of electrons, increase in oxidation number

reduction

gain of electrons, decrease in oxidation number

redox

a reaction that involves oxidation and reduction

oxidising agent

accepts electrons, is reduced in a redox reaction

reducing agent

donates electrons, is oxidised in a redox reaction

disproportionation

when an element of a single species is simultaneously oxidised and reduced

anode

positive electrode - site of oxidation

cathode

negative electrode - site of reduction

standard hydrogen electrode

a platinum electrode immersed in 1moldm-3 HCl, enclosed in a tube containing hydrogen gas under standard conditions

standard conditions

298K, 100KPa, 1moldm-3

standard electrode potential

the potential difference ( sometimes called voltage) produced when a standard half-cell is connected to a standard hydrogen cell under standard conditions

salt bridge

a porous substance soaked with a solution of an inert, strong electrolyte - salt ions flow through the bridge to complete the cell and balance the charges in solutions

electrochemical cell

produces electricity from a chemical reaction

storage cell

a cell that can be recharged when the current is passed in the opposite direction to the flow of curretn generated by the cell

fuel cell

a cell used to harness electricity from a chemical reaction

empirical formula

smallest whole number ratio of atoms of each element in a compound

molecular formula

the actual number of atoms of each element in a molecule

spectator ions

ions that do not take part in the reaction

standard solution

a solution with an accurately known concentration

displacement reaction

more reactive element reacts to take place of a less reactive element in a compound

precipitation reaction

reaction that produces an insoluble solid

concordant

results within +- 0.2cm3 of each other

atom economy

measure of the proportion of reaction atoms that become part of the desired product in the balanced chemical equation

enthalpy change

heat energy measured at a constant pressure

exothermic

heat given off, negative enthalpy change

endothermic

heat absorbed, positive enthalpy change

standard enthalpy change of reaction

enthalpy change for a reaction with quantities shown in a chemical equation under standard conditions

standard enthalpy change of formation

enthalpy change when one mol of a substance is formed from its constituent elements with all products and reactands at 298K and 100KPa

standard enthalpy change of combustion

enthalpy change when one mol of a substance is completely burned in oxygen with all products and reactants at 298K and 100KPa

standard enthalpy change of neutralisation

enthalpy change when one mol of water is formed in a reaction between an acid and alkali with all products and reactants at 298K and 100KPa

specific heat capacity

the amout of energy needed to raise a temperature of 1g of a substance by 1 degree

Hess’s law

the enthalpy change of a reaction is independent to the route taken

bond enthalpy

amount of energy required to break 1 mole of the stated bond in the gas phase

mean bond enthalpy

average amount of energy needed to break a specific type of bond, measured over a variety of different molecules

lattice energy of formation

enthalpy change when one mol of an ionic solid is formed from its constituent ions in the gaseous state

enthalpy change of atomisation

enthalpy change when one mol of gaseous atoms is formed from an element in its standard state

first electron affinity

enthalpy change required for each atom in one mol of gaseous atoms to lose an electron to form one mole of gaseous 1- ions

enthalpy change of hydration

enthalpy change when 1 mol of gaseous ions is completely hydrated

enthalpy change of solution

enthalpy change when one mol of an ionic solid is dissolved in an amount of water large enough so that all ions are separated and do not interact

lattice energy of dissociation

enthalpy change when one mol of an ionic solid is broken down into its constituent ions

entropy

a measure of the disorder of a system

Gibbs free energy

a measure of the feasibility of a chemcial reaction - does not take into account kinetic factors

homogeneous system

system where all chemicals are in the same phase

heterogeneous system

a system where not all chemicals are in the same phase

le chateliers principle

if a change is made to a system in dynamic equilibrium, the position of equilibrium moves to counteract this change

dynamic equilibrium

forward and backward reactions occur simultaneously, rate of forward reaction is equal to the rate of backward reaction and there is no change to the concentrations of the reactants and products

partial pressure

the pressure exerted by a particular gas in a mixture in a closed system

bronsted-lowry acid

proton donor

bronsted-lowry base

proton acceptor

pH

-log(H+)

strong acid

completely dissociates in solution

weak acid

only partially dissociates in solution

strong base

completely dissociates in solution

weak base

only partially protonated in solution

amphoteric

a substance that can act as an acid or base

equivalence point

the point when full neutralisation occurs

end point

the point in a titration when the indicator changes colour

buffer solution

a solution which resists changes in pH upon addition of small amounts of acid or alkali

transition metal

d-block elements that form one or more stable ions with imcompletely filled d orbitals

complex ion

a central metal cation surrounded by ligands

denticity

how many dative bonds a ligand can form

coordination number

number of dative covalent bonds that ligands from with the central metal ion

autocatalysis

when a product catalyses the reaction

homogeneous catalyst

catalyst is in same phase as reactants

heterogeneous catalyst

catalyst is in different phase to reactants

molecular ion peak

peak with highest m/z value

activation energy

minimum amount of kinetic energy required for particles to react