AQA Year 1 Physical Definitions Flashcards
Definitions
Mass Number
Number of protons and neutrons
Atomic Number
Number of protons
Isotopes
Atoms with the same number of protons, but a different number of neutrons
1st Ionisation Energy
Energy required to remove an electron from a gaseous atom.
Relative Atomic Mass
average mass of one atom of an element / 1/12th mass of an atom of 12C
Relative Molecular Mass
average mass of an entity / 1/12th mass of an atom of 12C
1 Mole
Avogadro�s number of particles
Empirical Formula
simplest ratio of atoms of each element in a compound
Molecular Formula
Actual number of atoms of each element in a compound
Electronegativity
The power of an atom to attract the pair of electrons from a covalent bond
Covalent Bond
shared pair of electrons
Co-ordinate Bond
a covalent bond, in which both electrons are donated by one atom
Ionic Bond
Strong electrostatic attraction between oppositely charged ions
Metallic Bond
Strong electrostatic attraction between positive ions and delocalised electrons.
Enthalpy Change
Heat change at constant pressure
Enthalpy of Combustion
The enthalpy change when 1 mol of a substance, Is completely burned in oxygen, under standard conditions, all substances in standard states
Enthalpy of Formation
The enthalpy change when 1 mol of a compound, is formed from its elements, under standard conditions, all substances in standard states
Hess�s Law
The enthalpy change in a reaction is independent of the route taken (and depends only on the initial and final states)
Bond Enthalpy
enthalpy required to break 1 mol of covalent bonds
Mean Bond Enthalpy
enthalpy required to break 1 mol of covalent bonds, averaged over a range of compounds
Rate of Reaction
Change in concentration / time
Activation Energy
The minimum energy for a reaction to occur
Catalyst
A substance that speeds up the rate of a reaction, but it is not used up
How a Catalyst Works
provides an alternative route, that has a lower activation energy
Dynamic Equilibrium
Forward rate = backward rate, concentrations remain constant
Le Chatelier�s Principle
equilibrium will shift to oppose the change.
Oxidation
Loss of electrons
Reduction
Gain of electrons
Oxidising Agent
A species that gains electrons
Reducing Agent
A species that loses electrons
