As Chemistry Unit 1 Key Definitions

Front 1

Isotopes

Back 1

Atoms of the same element with different number of neutrons.

Front 2

Atomic Number

Mass Number

Back 2

Number of protons in the nucleus of an atom.

Number of particles (protons and neutrons) in the nucleus.

Front 3

An Ion

Back 3

Positively or negatively charges atom or (covalently bonded) group of atoms (a molecular ion.

Front 4

Relative Isotopic Mass

Back 4

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

Front 5

Relative atomic mass (Ar)

Back 5

Weight mean mass of an atom of an element compared with one-twelth of the mass of an atom of carbon-12.

Front 6

Relative molecular mass (Mr)

Back 6

Weighted mean mass of a moloeculoar compared with one-twelth of the mass of an atom of carbon-12.

Front 7

Relative formular mass

Back 7

Weight mean mass of a formular unit compared with one-twelth of the mass of an atom of carbon-12.

Front 8

Amount of substance

Back 8

the quantity whoes unti is the mole. Chemists use 'amount of substance' as a means of counting atoms.

Front 9

Avogadro constant (Na)

Back 9

Number of atoms per mole of carbon-12 isotope. (6.02 x 10^23 mol-1)

Front 10

A Mole

Back 10

The amount of any substance containing as many particles as thre as carbon atoms in exactly 12g of the carbon-12 isotope.

Front 11

Molar Mass

Back 11

Mass per mole of a substance. The unit of molar mass are g mol -1.

Front 12

Empirical formula

Back 12

Simplest whole-number ratio of aroms of each element present in a compound.

Front 13

A molecule

Back 13

Small group of atoms held together by covalent bonds.

Front 14

Molecular Formula

Back 14

Actual number of atoms of each element in a molecule.

Front 15

Molar Volume

Back 15

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

Front 16

Concentration

Back 16

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

Front 17

Standard Solution

Back 17

A solution of known concentration. Standard solutions are normally used in titrations to determine unknown information abouth another substance.

Front 18

Species

Back 18

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

Front 19

Stoichiometry

Back 19

Molar relationship betwen the relative quantities of substances taking part in a reaction.

Front 20

Acid

Back 20

A species that is a prton donor.

Front 21

A Base

Back 21

A species that is a proton acceptor.

Front 22

Alkali

Back 22

Type of base that dissolves in water to form hydroxide ions.

Front 23

A Salt

Back 23

A chemical compound formed from an acid when an H+ ion from the acid has been replaced by a metal ion or another postive ion.

Front 24

A Cation

Back 24

Positively charged ion.

Front 25

An Anion

Back 25

Negatively charge ion.

Front 26

General Equations

Back 26

Front 27

Hydrated

Back 27

Refers to crystalline compound containing water molecules.

Front 28

Anhydrous

Back 28

Refers to a substance that contains no water molecules.

Front 29

Water of crystallisation

Back 29

Refers to the water molecules that form an essential part of the crystalline structure of a compund.

Front 30

Titrations

Back 30

Special type of volumetric analysis, in which you react a solution of an acid with a solution of a base.

Front 31

Oxidation Number

Back 31

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

Front 32

Oxidation

Reduction

Back 32

Loss of electrons or increase in oxidation number.

Gain of electrons or decrease in oxidation number.

Front 33

Redox reaction

Back 33

Reaction in which npth reduction and oxidation take place.

Front 34

Reducing agent

Oxidising agent

Back 34

Reagent that reduces (add electrons to) another species.

Reagent that oxidises (takes electrons from) another species.

Front 35

First ionisation energy

Back 35

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

Front 36

Electron Shielding

Back 36

Repulsion between electrons in different inner shells. Shielding reduces the net attractive force from the positive nucleus on the outer-shell electrons.

Front 37

Successive ionisation energies

Back 37

Measure of the energy required to remove each electron in turn.

Front 38

Second ionisation energy

Back 38

Energy required to remove one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions.

Front 39

A shell

Back 39

Group of atomic orbitals with the same principal quantum number, n. Also known as main energy level.

Front 40

Principal Quantum number, n

Back 40

The number representing the relative overall energy of each orbital, which increases with distance from the nucleus. The sets of orbitals with the same n-value are referred to as electron shells.

Front 41

Atomic orbital.

Back 41

A region that can hold up to two electrons, with opposite spins.

Front 42

A sub-shell

Back 42

Group of the same type of atomic orbitals (s, p, f or f) within a shell.