Foundations in Chemistry Key Terms

Relative molecular mass

mass of a molecule compared to the mass of an atom of carbon-12

relative formula mass

mass of a formula unit compared to the mass of an atom of carbon-12

standard solution

a solution of known concentration

ideal gas equation

pV = nRT

Strong Acid

Dissociates fully into H+ ions

Weak acid

Dissociates partially into H+ ions

Base / Alkali

Dissociates into OH- ions

Neutralisation

H+ ions react with OH- ions

% uncertainty

= uncertainty/measurement

Empirical Formula

Simplest whole number ratio of atoms of each element in a compound

Avogadro Constant = 6.02 × 10²³

Number of particles in 1 mole

Atomic number

Protons

Mass number

Protons + neutrons

Relative atomic mass

the weighted mean mass of an atom of an element compared with 1/12th the mass of a carbon-12 atom

relative isotopic mass

The mass of an isotope compared to 1/12th the mass of an atom of carbon-12

Isotopes

Atoms of an element with the same number of protons and electrons, but a different number of neutrons (different mass)

orbital

a region around the nucleus where it is likely to find an electron

1st Ionisation energy

the energy required to remove 1 mol of electrons from 1 mol of gaseous atoms to form 1 mol of gaseous 1+ ions

2nd Ionisation energy

the energy required to remove 1 mol of electrons from 1 mol of 1+ gaseous atoms to form 1 mol of gaseous 2+ ions

Ionic bond

the electrostatic attraction between positive and negative ions

Covalent bond

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

Dative covalent bond

where both electrons in the shared pair in the bond are supplied by 1 of the bonding atoms

VSEPR theory

valence-shell electron-pair repulsion theory

Linear - 180º

2 bonded pairs, 0 lone pairs

Trigonal Planar - 120º

3 bonded pairs, 0 lone pairs

Tetrahedral - 109.5º

4 bonded pairs, 0 lone pairs

Trigonal Pyramidal - 120º + 90º

5 bonded pairs, 0 lone pairs

Octahedral - 90º

6 bonded pairs, no lone pairs

Non-Linear - 104.5º

2 bonded pairs, 2 lone pairs

Pyramidal - 107º

3 bonded pairs, 0 lone pairs

electronegativity

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

polar bond

a small charge difference across a bond from different electronegativities of bonded atoms - permanent dipole

Hydrogen Bond

strong permanent dipole-dipole interaction between an electron deficient Hδ+ and lone pair on O

Metallic Bond

strong electrostatic attraction between pos. metal ions and neg. delocalised electrons

Periodicity

regular periodic variation of properties with atomic number and position in the periodic table