Chap 4 ( chemical bonding)

Anion

A negatively charged ion

Cation

A positively charged ion

Lattice

a regularly repeating arrangement of ions, atoms, or molecules in three dimensions throughout the whole crystal stucture

van der Waals forces

the weak forces of attraction between molecules, including either instantaneous (id-id) or permanent dipole - permanent dipole forces (pd-pd) (inclduing hydrogen bonding). The term is a general term to describe all intermolecular forces

Intermolecular forces

The weak forces between molecules

Ionic bonding

The electrostatic attraction between oppositely charged ions (cations and anions)

Electrovalent bond

Another name for an ionic bond

Dot and cross diagram

A diagram showing the arrangement of the outer-shell electrons in an ionic or covalent element or compound. The electrons are shown as dots or crosses to show their origin

Covalent bonding

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

lone pairs (of electrons)

Pairs of electrons in the outer shell of an atom that are not involved in the bonding

Double covalent bond

two shared pairs of electrons bonding two atoms together

Triple covalent bond

three shared pairs of electrons bonding two atoms together

E.g. N2

co-ordinate bond/ dative bond

the sharing of a pair of electrons between two atoms where both the electrons in the bond comes from the same atom.

It is represented with an arrow. Head of arrow points away from the lone pair that forms the bond

Electron deficient

an atom or molecule that has less than its usual share of electrons

E.g NH4+ = NH3 + H+ and AlCl3

Why are double bonds generally shorter than single bonds?

This is because double bonds have a greater quantity of negative charge between two atomic nuclei. The greater forces of attraction between the electrons and the nuclei pulls the atoms closer together, resulting in a stronger bond

Bond energy

the energy required to break one mole of a particular covalent bond in the gaseous state. The units of bond energy are kilojoules per mole, kJ/mol

Bond length

the distance between the nuclei of two covalently bonded atoms

Delocalised electrons

Electrons that are not associated with any particular atom. In metals, the delocalised electrons move throughout the metallic structure between the metal ions when a voltage is applied.

Metallic bonding

the electrostatic attraction between positive ions and delocalised electrons

Electronegativity

the power of a particular atom that is covalently bonded to another atom to attract the bonding pair of electrons towards itself.

Polar bonds

the electron pair in the bond is drawn towards the atom with the larger electronegativity, making one end of the molecule slightly positive compared with the other.

bond polarity

the partial separation of charge when two different atoms are joined by a covalent bond. This results in an unequal atrraction for the bonding pair of electrons

instantaneous dipole-induce dipole forces (id-id forces)

the weakest intermolecular attractive force. It results from temporary instantaneous dipoles induced in both polar and non-polar molecules. These forces are also called London Dispersion forces. The dipoles are not permanent. In this context 'induced' means that one molecule brings about an attractive or repulsive effect on another.

permanent dipole-permanent dipole forces (pd-pd forces)

attractive intermolecular forces which result from permanent dipoles in molecules

hydrogen bond

the strongest type of intermolecular forces but weakeer than covalent bonds. It is a strong type of pd-pd force.

Hydrolysis

the breakdown of a compound by water. Hydrolysis is also used to describe the breakdown of a substance by dilute acids or alkali

Surface tension

The ability of a liquid surface to resist any external forces