MUST KNOW Definitions

Question 1

Relative Atomic Mass Ar

Answer 1

the weighted average of the masses of its isotopes relative to 1/12 of the mass of a C12 atom

Question 2

Relative Molecular Mass Mr

Answer 2

the weighted average of the masses of the atoms in a molecule relative to 1/12 of the mass of a C12 atom

Question 3

Mass Number (A)

Answer 3

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

Question 4

Atomic Number (Z)

Answer 4

the number of protons in the nucleus of an atom

Question 5

Isotopes

Answer 5

atoms with the same atomic number but a different mass number

Question 6

Empirical Formula

Answer 6

the simplest whole number ratio of elements in a compound

Question 7

Molecular Formula

Answer 7

the actual number of atoms of each element in the formula of a compound

Question 8

Ionic Bond

Answer 8

Oppositely charged ions held together by an electrostatic attraction

Question 9

Covalent Bond

Answer 9

the electrostatic attraction between a positively charged nucleus and a shared pair of electrons, one electron supplied by each atom either side of the bond

Question 10

Dative Bond

Answer 10

a shared pair of electrons, both electrons being supplied by one atom in the bond

Question 11

First Ionisation Energy

Answer 11

the minimum amount of energy required in order to remove one mole of gaseous electrons from one mole of gaseous atoms to form one mole of gaseous positive ions

Question 12

Electronegativity

Answer 12

the ability of an atom to attract the pair of electrons in a covalent bond to itself

Question 13

Electron Affinity

Answer 13

The enthalpy change when one mole of gaseous atoms acquires one mole of electrons to form one mole of gaseous negative ions

Question 14

Exothermic Reaction

Answer 14

the heat of a reaction is given out to the surroundings

Question 15

Endothermic Reaction

Answer 15

the heat of a reaction is absorbed from the surroundings

Question 16

Average Bond Enthalpy

Answer 16

The energy required to break one mole of a particular covalent bond in the gaseous state to form gaseous atoms (under standard conditions)
it is an average value as it will be affected by neighbouring atoms

Question 16

Standard Enthalpy Change of a Reaction

Answer 16

the heat energy change under standard conditions (P= 100 kPa T=298K)

Question 17

Standard State

Answer 17

the state of an allotrope of an element or compound at standard conditions

Question 18

Standard Enthalpy of Formation

Answer 18

the enthalpy change when one mole of compound is formed in its standard state from its elements in the standard states

Question 19

Standard Enthalpy of Combustion

Answer 19

the enthalpy change when one mole of a substance undergoes complete combustion in its standard state (at STP)

Question 20

Standard Enthalpy of Atomisation

Answer 20

the enthalpy change when one mole of gaseous atoms is formed from the elements in its standard states (at STP)

Question 20

Lattice Enthalpy

Answer 20

the amount of energy required to dissociate one mole of an ionic compound to its gaseous ions (at STP)

Question 21

Electron Affinity

Answer 21

the enthalpy change when one mole of gaseous atoms accepts a mole of gaseous electrons (at STP)

Question 22

Rate of Reaction

Answer 22

change in concentration of reactant (or product) with time

Question 23

Activation Energy

Answer 23

the minimum amount of energy that colliding reactants require to exceed in order for a reaction to occur

Question 24

Oxidation

Answer 24

the loss of electrons
gain of oxygen
loss of hydrogen

Question 25

Reduction

Answer 25

the gain of electrons
the loss of oxygen
the gain of hydrogen

Question 26

Oxidising Agent

Answer 26

causes the other reacting species to be oxidised and itself reduced

Question 27

Reducing Agent

Answer 27

causes the other reacting species to be reduced and itself oxidised

Question 28

Delocalisation

Answer 28

electrons in p orbitals forming pi bonds but shared between more than two nuclei

Question 29

Resonance

Answer 29

when more than one Lewis Structure can represent the position of a double bond

Question 30

Sigma Bond

Answer 30

Results in the axial (end to end) overlap of orbitals, electron density is concentrated between the nuclei of bonding atoms

Question 31

Hybridisation

Answer 31

the mixing of atomic orbitals to form new orbitals of intermediate energy

Question 32

Pi Bond

Answer 32

results in the sideways overlap of parallel p orbitals, electron density is concentrated above and below the nuclei of bonding atoms