Chemistry Unit 1 Ocr As-Level Definitions Module

Front 1

Isotope

Back 1

An atom of the same element with different number of neutrons

Front 2

Atomic number

Back 2

The number of protons in the nucleus of an atom

Front 3

Mass/Nucleon Number

Back 3

The number of particles (protons and neutrons) in the nucleus of an atom.

Front 4

Relative isotopic mass

Back 4

The mass of an atom of an isotope compared with one-twelfth the mass of an atom of carbon-12.

Front 5

Relative atomic mass

Back 5

The weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12.

Front 6

Relative molecular mass, (Mr)

Back 6

The weighted mean mass of a molecule compared with one-twelfth of the mass of an atom of carbon-12.

Front 7

Relative formula mass

Back 7

The weighted mean mass of a formula unit compared with one-twelfth of the mass of an atom of carbon-12.

Front 8

Amount of substance

Back 8

The quantity whose unit is the mole, used as a means of counting atoms.

Front 9

Avogadro constant, NA

Back 9

The number of atoms per mole of the carbon-12 isotope (6.02x10^23 mol^-1).

Front 10

Mole

Back 10

Amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope. (6.02x10^23).

Front 11

Molar mass, M

Back 11

The mass per mole of a substance. The units of molar mass are g mol^-1 (grams per mole).

Front 12

Empirical formula

Back 12

The simplest whole-number ratio of atoms of each element present in a compound.

Front 13

Molecule

Back 13

A small group of atoms held together by covalent bonds.

Front 14

Molecular formula

Back 14

The actual number of atoms of each element in a molecule.

Front 15

Molar volume

Back 15

The volume per mole of a gas. The units of molar volume are dm^3 mol^-1. At room temperature and pressure, the molar volume is approximately 24.0 dm^3 mol^-1.

Front 16

Concentration

Back 16

Amount of solute, in mol, dissolved per 1dm^3 (1000cm^3) of solution.

Front 17

Standard solution

Back 17

A solution of known concentration. They are usually used in titrations to determine unknown information about another substance.

Front 18

Species

Back 18

Any type of particle that takes part in a chemical reaction.

Front 19

Stoichiometry

Back 19

The molar relationship between relative quantities of substances taking part in a reaction (species).

Front 20

Acid

Back 20

A species that is a proton (H+ ion) donor.

Front 21

Base

Back 21

A species that is a proton (H+ ion) acceptor.

Front 22

Alkali

Back 22

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

Front 23

Salt

Back 23

Any chemical compound formed from an acid when a Proton (H+ ion) from the acid has been replaced by a metal ion or another positive ion, such as the ammonium ion, NH4^+

Front 24

Hydrated

Back 24

A crystalline compound containing water molecules.

Front 25

Anhydrous

Back 25

A substance that contains no water molecules.

Front 26

Water of crystallisation

Back 26

Water molecules that form an essential part of the crystalline structure of a compound.

Front 27

Oxidation number

Back 27

A measure of the number of electrons that an atom uses to bond with atoms of another element.

Front 28

Oxidation

Back 28

The loss of electrons or an increase of oxidation number.

Front 29

Reduction

Back 29

A gain of electrons or a decrease in oxidation number.

Front 30

Redox reaction

Back 30

A reaction in which both reduction and oxidation take place.

Front 31

Reducing agent

Back 31

A reducing agent is a reagent that reduces (adds electrons to) another species.

Front 32

Oxidising agent

Back 32

A reagent that oxidises (takes electrons from) another species).

Front 33

Explain why ice is less dense than water, in terms of hydrogen bonding.

Back 33

Ice is less dense than water as the hydrogen bonds in ice are longer and thus space the molecules out more. In water, the hydrogen bonds collapse, not as rigid and are closer together.