Unit 1 Definitions

Question 0

Nucleons

Answer 0

Protons and neutrons (sub-atomic particles found in the nucleus).

Question 1

Atomic Number (Z)

Answer 1

The number of protons in the nucleus.

Question 2

Mass Number (A)

Answer 2

The total number of protons and neutrons in the nucleus of an atom.

Question 3

Isotopes

Answer 3

Atoms with the same number of protons but different numbers of neutrons in their nuclei.

Question 4

Abundance (of isotopes)

Answer 4

The ratio of the number of atoms of a particular isotope in a sample of an element to the number of atoms of a specified isotope, or to the total number of atoms of the element.

Question 5

Relative Atomic Mass (Ar)

Answer 5

Average mass of an atom / 1/12th mass of 1 atom of carbon-12

Question 6

Allotrope

Answer 6

Pure element that can exist in different physical forms in which their atoms are arranged differently. Eg: diamond, graphite and buckminsterfullerene are all allotropes of carbon

Question 7

Relative Molecular Mass (Mr)

Answer 7

Average mass of a molecule / 1/12th mass of one atom of carbon-12

Question 8

Avogadro Constant (L)

Answer 8

The number of particles in a mole of substance.

Avogadro number = 6.022x10^23

Question 9

The mole (mol)

Answer 9

A quantity of a substance that contains the Avogadro number of particles (eg. atoms, ions or molecules)

Question 10

cm^3

Answer 10

centimetre

1 centimetre^3 = 1 millilitres

Question 11

dm^3

Answer 11

decimetre

1decimetre^3 = 1 litre

Question 12

Molarity (M)

Answer 12

The concentration of a solution measured in moles of solvent per cubic decimetre of solution.

Question 13

Empirical Formula

Answer 13

The simplest whole number ratio in which the atoms in a compound combine together.

Question 14

Molecular Formula

Answer 14

A formula that tells us the numbers of atoms of each different element that make up a molecule of a compound.

Question 15

Percentage Yield

Answer 15

(Actual amount of product produced / theoretical amount - predicted from chemical equation) x100.

Question 16

Percentage Atom Economy

Answer 16

This describes the efficiency of a chemical reaction by comparing the total number of atoms in the product with the total number in the reactants.
(mass of product / mass of reactants) x100

Question 17

Ideal Gas Equation

Answer 17

pV=nRT

Question 18

Metallic Bonding

Answer 18

A chemical bond in which outer electrons are spread over a lattice of metal ions in a delocalised system.

Question 19

Ionic Bonding

Answer 19

Chemical bond in which an electron or electrons are transferred from one atom to another. This results in the formation of oppositely charged ions with electrostatic forces of attraction between them.

Question 20

Covalent Bonding

Answer 20

Chemical bond in which electrons are shared between two atoms.

Question 21

Dative Covalent Bonding (coordinate bond)

Answer 21

Covalent bonding in which both the electrons in the bond come from one of the atoms in the bond.

Question 22

Electronegativity

Answer 22

The power of an atom to attract electrons in a covalent bond.

Question 23

Polar Bond (dipole)

Answer 23

A covalent bond between atoms of different electronegativities. there are oppositely charges separated by a short distance in the molecule or ion.

Question 24

Polar molecule (permanent dipole)

Answer 24

Attractive forces that exist between polar molecules.

Question 25

Intermolecular Forces

Answer 25

Weak attractive force between molecules.

Question 26

Dipole-Dipole Force

Answer 26

An intermolecular force that results from the attraction between molecules with permanent dipoles.

Question 27

Hydrogen Bonding

Answer 27

An intermolecular force in which a hydrogen atom covalently bonded to an electronegative atom interacts with another electronegative atom.

Question 28

van der Waals force

Answer 28

An intermolecular force of attraction that is caused by instantaneous dipoles and acts between all atoms and molecules.

Question 29

Fractional Distillation

Answer 29

A method of separating mixtures of liquids or gases according to their boiling points.

Question 30

Fraction

Answer 30

A mixture of hydrocarbons collectedover a particular range of boiling points during the fractional distillation of crude oil.

Question 31

Hydrocarbon

Answer 31

A compound containing only hydrogen and carbon atoms.

Question 32

Homologous Series

Answer 32

A set of organic compounds with the same functional group. The compounds differ in the length of their hydrocarbon chains.

Question 33

Functional Group

Answer 33

An atom or group of atoms in an organic molecule which is responsible for the characteristic reactions of that molecule.

Question 34

Structural Isomers

Answer 34

When two or more compounds have the same molecular formula, but different structures.

Question 35

Chain Isomers

Answer 35

A type of structural isomerism in which compounds have identical molecular formula but their carbon atoms are joined together in a different arrangements. This involves branched and unbranched carbon chains.

Question 36

Positional Isomerism

Answer 36

A type of isomerism where the functional group can be joinedat different places on the carbon skeleton.

Question 37

Functional Group Isomerism

Answer 37

A type of structural isomerism where the isomers contain different functional groups, they belong to a different homologous series.

Question 38

Cracking

Answer 38

The breaking of long-chain alkanes molecules (obtained from crude oil) into shorter chain hydrocarbons, some of which are alkenes.

Question 39

Homolysis (Homolytic fission)

Answer 39

Breaking of a covalent bond so that each atom takes one electron from the shared pair, becoming a radical.

Question 40

Heterolysis (Heterolytic fission)

Answer 40

Breaking of a chemical bond so that only one atom takes both electrons, ions are formed.

Question 41

Free Radical

Answer 41

A chemical species with an unpaired electron - usually highly reactive.

Question 42

Enthalpy Change

Answer 42

The heat transferred in a reaction at constant pressure (unit: kJ/mol)

Question 43

Endothermic Reaction

Answer 43

Reaction gives out energy - delta H is negative.

Question 44

Endothermic Reactions

Answer 44

Reaction absorbs energy - delta H is positive.

Question 45

Standard Enthalpy Change

Answer 45

The enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation, under standard conditions in their standard states.

Question 46

Standard Enthalpy Change of Formation

Answer 46

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

Question 47

Standard Enthalpy Change of Combustion

Answer 47

The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions.

Question 48

Hess' Law

Answer 48

If a reaction can occur by more than one route, the overall enthalpy change is independent of the route taken.

Question 49

Bond Dissociation Enthalpy

Answer 49

The enthalpy change required to break a covalent bond with all species in the gaseous state

Question 50

Mean Bond Enthalpy

Answer 50

The average value of the bond dissociation enthalpy for a given type of bond taken from a range of different compounds.

Question 51

Oxidation State

Answer 51

The number of electrons which must be added to the species to convert it to the neutral atom

Question 52

Disproportionation

Answer 52

A reaction in which a species is simultaneously oxidised and reduced

Question 53

Carbon-neutral

Answer 53

An activity where there is no net annual carbon emissions into the atmosphere

Question 54

Hydration

Answer 54

The addition of water to a molecule/compound

Question 55

Stereoisomerism

Answer 55

Compounds with the same structural formula but with a different spatial arrangement/ different orientation

Question 56

Nucleophile

Answer 56

Electron-pair doner