Glossary

bond energy - the energy needed to break onemole of a given bond in a gaseous molecule. a base.

co-ordinate bond (or dative covalent bond) – a covalent bond in which both electrons in the bond come from the same atom.

covalent bond - a bond formed by the sharing of pairs ofelectrons between two atoms.

delocalised electrons – electrons that are not associated with any one particular atom or bond.

dipole–dipole forces – the forces between two molecules having permanent dipoles.

dot-and-cross diagram – a diagram showing the arrangement of the outer-shell electrons in an ionic or covalent element or compound.

intermolecular forces – the weak forces between molecules.

ionic bond – the electrostatic attraction between oppositely charged ions.

hybridization - the process of mixing atomic orbitals so that each has some character of each of the orbitals mixed.

hydrogen bonding - the strongest type of intermolecular force. It is formed between molecules having a hydrogen atom bonded to one of the most electronegative elements (F, O or N).

lone pairs (of electrons) – pairs of electrons in the outer shell of an atom that are not bonded.

metallic bonding – the strong attractive forces (bond) between the positively charged ions and the delocalized electrons.

pi (π) bonds – multiple covalent bonds involving thesideways overlap of p atomic orbitals.

sigma (σ) bonds – single covalent bonds formed by the overlap of atomic orbitals.

spin-pair repulsion – electrons repel each other as they have the same charge. Electrons arrange themselves so that they first singly occupy different orbitals in the same sublevel.

van der Waals’ forces – very weak forces of attraction between all atoms or molecules.

Practice Exercises