AS chemistry definitions

Question 1

“isotope”

Answer 1

Isotopes are atoms of the same element that contain the same number of protons and electrons but a different number of neutrons

Question 2

first ionisation energy

Answer 2

The first ionisation energy (IE1) is the energy required to remove one mole of electrons from one mole of atoms of an gaseous state element to form one mole of gaseous state 1+ ions

Question 3

“unified atomic mass”

Answer 3

“one twelfth of the mass of a carbon-12 atom”

Question 4

“relative atomic mass”

Answer 4

relative atomic mass (Ar) of an element is the weighted average mass of the atoms in a given sample of an element compared to the unified atomic mass unit

Question 5

relative isotopic mass

Answer 5

The relative isotopic mass is the mass of a particular atom of an isotope compared to the value of the unified atomic mass unit

Question 6

“relative molecular mass”

Answer 6

The relative molecular mass (Mr) is the ratio of weighted average mass of a molecule of a molecular compound to the unified atomic mass unit

Question 7

relative formula mass

Answer 7

The relative formula mass is the weighted average mass of one formula unit compared to the unified atomic mass unit

Question 8

Avogadro constant

Answer 8

The Avogadro constant (NA or L) is the number of particles equivalent to the relative atomic mass or molecular mass of a substance.

Question 9

empirical formula

Answer 9

the simplest whole number ratio of the elements present in one molecule or formula unit of a compound

Question 10

“molecular formula”

Answer 10

“formula that shows the number and type of each atoms in an molecule”

Question 11

“electronegativity”

Answer 11

“power of an atom to attract electrons to itself”

Question 12

ionic bonding

Answer 12

electrostatic attraction between oppositely charged ions (positively charged cations and negatively charged anions)

Question 13

metallic bonding

Answer 13

“electrostatic attraction between positive metal ions and delocalised electrons”

Question 14

“covalent bonding”

Answer 14

“electrostatic attraction between the nuclei of two atoms and a shared pair of electrons”

Question 15

“bond energy”

Answer 15

“the energy required to break one mole of a particular covalent bond in the gas state”

Question 16

bond length

Answer 16

” internuclear distance of two covalently bonded atoms”

Question 17

“standard conditions “

Answer 17

temperature of 273 K and pressure 1atm

Question 18

enthalpy change of reaction

Answer 18

ΔHr
“the enthalpy change when the reactants in the stoichiometric equation react to give the products under standard conditions”

Question 19

enthalpy change formation

Answer 19

ΔHf
“the enthalpy change when one mole of a compound is formed from its elements under standard conditions”

Question 20

enthalpy change combustion

Answer 20

ΔHc
“the enthalpy change when one mole of a substance is burnt in excess oxygen under standard conditions”

Question 21

enthalpy change of neutralisation

Answer 21

ΔHneut
“the enthalpy change when one mole of water is formed by reacting an acid and an alkali under standard conditions”

Question 22

“Le Chatelier’s principle”

Answer 22

Le Chatelier’s principle says that if a change is made to a system at dynamic equilibrium, the position of the equilibrium moves to minimise this change.

Question 23

“activation energy”

Answer 23

EA
The activation energy is the minimum amount of energy that particles require in order for a successful collision to occur which will cause the reaction to happen.

Question 24

hydrocarbon

Answer 24

“compound made up of C and H atoms only”