Chemistry A-level OCR keywords

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50 Terms

1

mole

The amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12 g of the carbon-12 isotope which is 6.023 x 10^23.

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2

molar mass

the mass of one mole of a substance, in units of g mol^-1

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3

Molar gas volume

The volume per mole of gas molecules at a stated temperature and pressure

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4

Empirical formula

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

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5

Water of crystallisation

Water molecules that are bonded into a crystalline structure of a compound

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6

Amount of substance

The quantity whose unit of the mole, used for counting any species such as atoms ions or molecules.

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7

Anhydrous

without water

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8

Avagadro's constant

The number of atoms per mole of the carbon-12 isotope. 6.023 x 10^23

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9

ionic bonding

The electrostatic attraction between oppositely charged ions

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10

Covalent bonding

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

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11

Dative covalent bond/ coordinate bond

A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only.

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12

Dipole

A separation in electrical charge so that one atom of a polar covalent bond, or one end of a polar molecule, has a small positive charge and the other has a small negative charge

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13

London forces

Attractive forces between induced dipoles in different molecules; also known as induced dipole-dipole interactions

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14

Electronic configuration

A shorthand representation that shows how electrons occupy sub-shells in an atom

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15

Electronegativity

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

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16

Endothermic reaction

A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings (+ve).

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17

Enthalpy

The heat content that is stored in a chemical system

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18

Enthalpy change

The difference between the enthalpy of the products and the enthalpy of the reactants

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19

Exothermic reaction

A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (-ve).

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20

First ionisation energy

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

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21

Displayed formula

A formula showing the relative positioning of all the atoms in a molecule and the bonds between them.

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22

General formula

The simplest algebraic formula of a member of a homologous series

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23

Hydrated

A crystalline compound containing water molecules

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24

Hydrogen bond

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.

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25

Intermolecular force

forces of attraction between molecules

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26

Ion

a positively or negatively charged atom

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27

Isotope

Atoms of the same element that have different numbers of neutrons and different masses.

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28

Lone pair

An outer shell pair of electrons that is not involved in chemical bonding

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29

Metallic bond

The electrostatic attraction between positive metal ions and delocalised electrons.

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30

molecular formula

A formula that shows the number and type of atoms of each element present in a molecule

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31

Permanent dipole

A small charge difference that does not change across a bond, with positive and negative partial changes on the bonded atoms: the result of a bonded atoms having different electronegativities

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32

Permanent dipole-dipole interaction

An attractive force between permanent dipoles in neighbouring polar molecules.

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33

Polar covalent bond

A bond with a permanent dipole, having partial charges on the bonded atoms.

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34

Polar molecule

A molecule with an overall dipole, having taken into account any dipoles across bonds and the shape of the molecule

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35

Relative atomic mass

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

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36

Relative formula mass

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

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37

Relative isotopic mass

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

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38

Relative molecular mass

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

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39

Shielding

the repulsion between electrons in different inner shells . It reduces the net attractive force between the positive nucleus on the outer shell electrons

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40

Surroundings

Everything that is not the chemical system

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41

System

The chemicals involved in the reaction

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42

Stoichiometry

The ratio of the amount, in moles, of each substance in a chemical reaction

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43

Standard state

The physical state of a substance under standard conditions of 100kPa and a stated temp (usually 298K)

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44

Standard solution

a solution of known concentration

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45

Standard conditions

298K,101kPa pressure (1 atm), 1 moldm^-3 when using solutions.

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46

Standard enthalpy change of combustion

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

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47

Standard enthalpy change of formation

the enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions.

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48

Standard enthalpy change of reaction

The enthalpy change associated with any chemical reaction as shown by a chemical equation.

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49

Hess’ Law

The overall enthalpy change for a chemical reaction is the same regardless of the number of steps in the reaction

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50

Average bond enthalpy

The amount of energy required to break a bond.

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