Chemistry AS level definitions already graded A

Element a substance made up of 1 type of atom Compound a substance made up of more than 1 type of atom - chemically bonded 00:02 01:39 Atom the smallest electrically neutral particle of an element that can take part in a chmeical change Molecule the smallest electrically neutral particle of an element or compound that can exist on its own The mole the amount of substance which contains the same number of particles as there are carbon atoms in 12g of carbon-12. This number is 6.02x10(23), it's called Avogadro's number. Molar mass the mass in grams of 1 mole Relative atomic mass (Ar) the mass of a single atom on a scale of which the mass of an atom of carbon-12 is 12 atomic mass units Amount of moles mass(g) / molar mass Standard enthalpy change of a reaction the energy transferred when the molar quantities of reactants as stated in the equation react under standard conditions Standard enthalpy change of combustion the enthalpy change when 1 mole of the substance burns completely in oxygen under standard conditions Standard enthalpy change of neutralisation the enthalpy change when the amounts of acid and alkali in the equation for the reaction neutralise each other under standard conditions Standard enthalpy of formation the enthalpy change when 1 mole of the compound forms from its elements under standard conditions with the elements and the compound in their standard (stable) state