Chemistry A Level Ocr Specification Explanations

Front 1

Amount of Substance

Back 1

The quantity whose unit is the mole. Chemists use 'amount of substance' as a means of counting atoms

Front 2

The Mole

Back 2

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

Front 3

Avogadro Constant

Back 3

The number of atoms per mole of the carbon-12 isotope (6.02 x 10^23 mol^-1)

Front 4

Empirical Formula

Back 4

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

Front 5

Molecular Formula

Back 5

The actual number of atoms of each element in a molecule

Front 6

Anhydrous

Back 6

A substance that contains n water molecules

Front 7

Hydrated

Back 7

Crystalline and containing water molecules

Front 8

Water of Crystallisation

Back 8

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

Front 9

shape of a simple molecule is determined by _____________

Back 9

repulsion between electron pairs surrounding a central atom

Front 10

lone pairs of electrons repel less/more than bonded pairs

Back 10

more

Front 11

A permanent dipole may arise when ____, resulting in a _____ ____

Back 11

covalently-bonded atoms have different electronegativities

polar bond

Front 12

Shapes of Molecules:
Linear

Back 12

Bond angle = 180
e.g. CO2

Front 13

Shape of Molecules:
Non-Linear

Back 13

Bond angle = 104.5
e.g. H2O

Front 14

Shapes of Molecules:
Trigonal Planar

Back 14

Bond angle = 120
e.g. BF3

Front 15

Shapes of Molecules:
Tetrahedral

Back 15

Bond angle = 109.5
e.g. CH4

Front 16

Shapes of Molecules:
Pyramidal

Back 16

Bond angle = 107
e.g. N(dative)H3

Front 17

Shapes of Molecules:
Octahedral

Back 17

Bond angle = 90
e.g. SF6