Definitions (Learn)

Question 1

Isotope

Answer 1

Atoms of the same element with different numbers of neutrons and different masses

Question 2

Relative atomic mass

Answer 2

The weighted mean mass of an atom of an element compared with one–twelfth of an atom of carbon–12

Question 3

1st ionisation energy

Answer 3

The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous +1 ions

Question 4

Shell

Answer 4

A group of atomic orbitals with the same principal quantum number, n, also known as a main energy level.

Question 5

Subshell

Answer 5

A group of orbitals of the same type within a shell.

Question 6

Atomic orbital

Answer 6

A region around the nucleus which can hold up to 2 electrons, with opposite spins.

Question 7

Electronegativity

Answer 7

A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond.

Question 8

Hydrogen bond

Answer 8

A strong dipole-dipole attraction between an electron deficient hydrogen atom of -NH, -OH or HF on one molecule and a lone pair of electrons on a highly electronegative atom containing N, O or F on a different molecule.

Question 9

Acid

Answer 9

A species that releases H+ ions in aqueous solution

Question 10

Strong acid

Answer 10

An acid that dissociates completely in solution

Question 11

Weak acid

Answer 11

An acid that dissociates only partially in solution

Question 12

Base

Answer 12

A compound that neutralises an acid to form a salt

Question 13

Alkali

Answer 13

A type of base that dissolves in water forming hydroxide ions, OH-
(Aq) ions

Question 14

Salt

Answer 14

The product of a reaction in which the H+ ions from the acid are replaced by either ammonium or metal ions

Question 15

Oxidation

Answer 15

A loss of electrons or an increase in oxidation number

Question 16

Reduction

Answer 16

Gain of electrons or a decrease in the oxidation number.

Question 17

Redox reaction

Answer 17

A reaction involving both oxidation and reduction

Question 18

Homologous series

Answer 18

A series of organic compounds with the same functional group but with each successive member differing by CH2

Question 19

Electrophile

Answer 19

An atom or a group of atoms which is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond.

Question 20

Stereoisomers

Answer 20

Compounds with the same structural formula but a different arrangement of atoms in space

Question 21

E/Z isomerism

Answer 21

A type of stereoisomerism in which different groups attached to each carbon of a C=C of a double bond may be arranged differently in space because of the restricted rotation of the C=C bond.

Question 22

Cis-trans isomerism

Answer 22

A special type of E/Z isomerism in which there are two non-hydrogen groups and two hydrogen atoms around the C=C double bond: the cis isomer (Z isomer) has H atoms on each carbon atom on the same side; the trans isomer (E isomer) has H atoms on each carbon on different sides.

Question 23

Enthalpy change of combustion

Answer 23

the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard condition, all reactants and products being in their standard states.

Question 24

Enthalpy change of formation

Answer 24

the enthalpy change that takes place when one mole of a compound in its standard state is formed from its constituent elements in their standard states under standard conditions.

Question 25

Enthalpy change of neutralisation

Answer 25

The standard enthalpy change of neutralisation is the enthalpy change when solutions of an acid and an alkali react together under standard conditions to produce 1 mole of water.

Question 26

Nucleophile

Answer 26

An atom/group that is attracted to an electron-deficient centre, where it donates a pair of electrons to form a new covalent bond.