definitions

Question 1

periodicity

Answer 1

the occurrence of patterns in the periodic table.

Question 2

atomic size

Answer 2

the covalent radius is half the distance between the nuclei of two bonded atoms of the element.

Question 3

first ionisation

Answer 3

the energy required to remove one electron from each atom of one mole of gaseous atoms.

Question 4

second ionisation

Answer 4

the energy required to remove one electron from each singly positive ion of one mole of the gaseous ions.

Question 5

electronegativity

Answer 5

a measure of the attraction an atom involved in a bond has for the electrons of the bond

Question 6

metallic bond

Answer 6

the electrostatic force of attraction between the positively charged ions and the delocalised electrons.

Question 7

covalent bond

Answer 7

a single covalent bond consists of one shared pair of electrons.

Question 8

non-polar covalent bond

Answer 8

when atoms of the same element form a covalent bond, the electrons are shared equally. these atoms have the same electronegativity.

Question 9

polar covalent

Answer 9

when atoms of different elements share electrons, atoms with different electronegativity values will share the pair of bonding electrons unequally, forming partial charges of a permanent dipole.

Question 10

ionic bond

Answer 10

due to periodic trends in electronegativity, elements far apart in the periodic table are more likely to form ionic rather than covalent bonds.

Question 11

van der waals

Answer 11

the forces of attraction that hold discrete atoms (noble gases) and discrete molecules (diatomics) together in the liquid state.

Question 12

london dispersion forces in monatomic elements

Answer 12

london dispersion forces are very weak, resulting in the noble gases having very low melting and boiling points.

Question 13

temporary or instantaneous (induced) dipoles

Answer 13

one side of the atom has a slight negative charge and the other side has a slightly positive charge.

Question 14

london dispersion forces in discrete molecules

Answer 14

london dispersion forces are formed as a result of electrostatic attractions between temporary and induced dipoles caused by the movement of electrons.

Question 15

permanent dipole - permanent dipole

Answer 15

a covalent bond in which the atoms have a ifference in electronegativity is a polar covalent bond.

Question 16

hydrogen bonds

Answer 16

electrostatic forces of attraction between molecules that contain highly polar bonds ( N, O, F)

Question 17

behaviour in an electric field

Answer 17

if a charged rod is held up to a stream of liquid, the permanent dipoles of polar liquids become attracted to the charged rod.

Question 18

viscosity

Answer 18

the resistance to flow

Question 19

solubility/miscibility

Answer 19

very polar molecules such as water do not mix with non-polar molecules such as oil and form two layers.

Question 20

oxidation

Answer 20

loss of electrons by a reactant in any reaction.

Question 21

reduction

Answer 21

gain of electrons by a reactant in any reaction.

Question 22

redox reaction

Answer 22

one in which both oxidation and reduction steps occur.

Question 23

oxidising agent

Answer 23

a substance which accepts/gains electrons during a chemical reaction. (itself reduced)

Question 24

reducing agent

Answer 24

a substance which donates/loses electrons during a chemical reaction. (itself oxidised)

Question 25

standard solution

Answer 25

a solution of which the concentration is accurately known.

Question 26

self-indicating reaction

Answer 26

a colour change involving one of the reactants indicating the end point of the reaction.

Question 27

chromatography

Answer 27

allows chemists to separate substances in complex mixtures.

Question 28

disclosing agent

Answer 28

a spray which causes the amino acids to show up as coloured spots.

Question 29

gas-liquid chromatography

Answer 29

mobile phase is an inert gas

Question 30

stationary phase

Answer 30

a very thin layer of a high boiling point, inert liquid absorbed onto an inert solid support.

Question 31

retention time

Answer 31

the amount of time that a substance takes to pass through the column.

Question 32

activation energy

Answer 32

the minimum kinetic energy with which particles have to collide in order to react.

Question 33

activated complex

Answer 33

an unstable arrangement of atoms, intermediate between reactants and products, formed at the maximum of the potential energy barrier during a reaction.

Question 34

temperature

Answer 34

a measure of the average kinetic energy of all the particles in a substance.

Question 35

enthalpy change

Answer 35

the energy difference between the products and the reactants and is the overall enthalpy change for a reaction.

Question 36

enthalpy of combustion

Answer 36

the energy released when one mole of a substance is burned completely in oxygen.

Question 37

bond enthalpy

Answer 37

the energy required to break one mole of a particular bond between a pair of atoms in the gaseous state.

Question 38

equilibria

Answer 38

a reaction is at equilibrium when the rate of the forward and reverse reaction are equal and the concentration of reactants and products remain constant.

Question 39

condensation reaction (esterification)

Answer 39

a reaction where a molecule of water is eliminated as two molecules join.

Question 40

hydrolysis

Answer 40

the splitting of a molecule by reaction with water.