Core AS Definitions

Question 1

Element

Answer 1

A substance containing only one type of atom

Question 2

Compound

Answer 2

A substance containing more than one type of atom chemically bonded to each other

Question 3

Mixture

Answer 3

A combination of two or more substances that are not chemically bonded to each other

Question 4

Molecule

Answer 4

A small number of atoms joined together with covalent bonds

Question 5

Particle

Answer 5

A general term used to describe any small portion of matter

Question 6

Atom

Answer 6

The smallest component of an element

Question 7

Atomic number

Answer 7

The number of protons in the nucleus of an atom

Question 8

Mass number

Answer 8

The mumber of protons and neutrons in the nucleus of an atom

Question 9

Isotopes

Answer 9

Atoms of the same element with a different number of neutrons and different masses

Question 10

Relative isotopic mass

Answer 10

The mass of one atom of an isotope compared with 1/12th of the mass of one atom of C-12

Question 11

Relative atomic mass

Answer 11

The weighted mean mass of an atom of an element compared with 1/12 of the mass of one atom of C-12

Question 12

Mole

Answer 12

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

Question 13

Avogadro’s constant

Answer 13

The number of particles per mole of a substance (6.02×10^23)

Question 14

Molar mass

Answer 14

The mass per mole of a substance (gmol^-1)

Question 15

Empirical formula

Answer 15

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

Question 16

Molecular formula

Answer 16

The actual number of atoms of each element present in a compound

Question 17

Strong acid

Answer 17

A proton donor, which is fully dissociated in aqueous solution

Question 18

Weak acid

Answer 18

A proton donor which is partially dissociated in aqueous solution

Question 19

Neutralisation

Answer 19

The reaction of an acid with a base to form a salt

Question 20

Base

Answer 20

A proton acceptor

Question 21

Alkali

Answer 21

A soluble base that releases OH- ions when in aqueous solution

Question 22

Salt

Answer 22

A compound produced when one or more H+ ions from an acid is replaced by a metal ion or another positive ion

Question 23

Water of crystallisation

Answer 23

The water present in a compound giving the compound a crystalline appearance

Question 24

Anhydrous

Answer 24

When all the waters of crystallisation have been removed from a compound

Question 25

Hydrated

Answer 25

When water of crystallisation is present in a compound

Question 26

Atomic orbital

Answer 26

A region around the nucleus of an atom that can hold up to two electrons with opposite spins

Question 27

s/p/d block element

Answer 27

Highest energy electron is in an s/p/d sub-shell/orbital

Question 28

Metallic bond

Answer 28

Strong electrostatic attraction between lattice of metal cations and delocalised electrons

Question 29

Ionic bond

Answer 29

The strong electrostatic attraction between lattice of positive and negative ions

Question 30

Covalent bond

Answer 30

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

Question 31

Dative covalent (co-ordinate) bond

Answer 31

The sharing of a pair of electrons between two atoms where only one of the atoms supplies both the electrons shared

Question 32

Electronegativity

Answer 32

The ability of an atom to attract the bonding pair of electrons toward itself in a covalent bond

Question 33

Periodicity

Answer 33

The repeating pattern of trends in physical and chemical properties across different periods

Question 34

Hydrogen bonding

Answer 34

Intermolecular bonding between the electron deficient H atom of -NH, -OH, or HF on one molecule and a lone pair of electrons on the highly electronegative N, O, or F atom of another molecule