Bond angle
The angle that is found between two bonds bonded from the same atom in a covalently bonded compound.
Bond length
Internuclear distance between two covalently bonded atoms.
Cation
A positively charged ion, formed when an atom loses at least one electron, e.g.Na +.
Covalent bond
The strong electrostatic attraction between two nuclei and the shared pair of electrons between them. Polar covalent bonds occur when there is an asymmetric electron distribution within the covalent bond due to difference in electronegativities.
Covalent substance
A substance that is made up of atoms that are covalently bonded to each other.
Dative covalent bonding
Occurs when one atom donates both electrons in a covalent bond.
Anion
A negatively charged ion, formed when an atom gains at least one electron, e.g. S 2 -.
Delocalised electrons
The electrons that are not contained within a single atom or a covalent bond.
Double bond
A covalent bond between two atoms involving four bonding electrons, as opposed to two in a single bond.
Electrical conductivity
A measure of the amount of electrical current a material can carry or its ability to carry the current.
Electron density map
Maps which show the region around a nucleus in which electrons are distributed. A high density corresponds to a high probability of an electron being there. They are used to infer the type of bonding present in a species.
Electron pair repulsion
Repulsion between electron pairs which means that the shape a molecule adopts has the electron pairs positioned as far apart as possible. As a result, carbon atoms in alkanes have a tetrahedral shape and a bond angle of 109.5°.
Electronegativity
The ability of an atom to attract the bonding electrons in a covalent bond. The most electronegative elements (N,O,F) are small and have a relatively high nuclear charge.
Electrostatic attraction
The attraction between two species with opposite charges.
Giant atomic structure
Large structures containing lots of atoms that are covalently bonded to each other. They are usually arranged in a regular lattice. E.g. Diamond.
Giant ionic lattice
A regular repeating structure made up of oppositely charged ions.
Ionic bond
Strong electrostatic attraction between two oppositely charged ions. The strength of attraction depends on the relative sizes and charges of ions.
Ionic charge
The electrical charge of an ion caused by the gain (negative charge) or loss (positive charge) of electrons. The magnitude of the charge is related to how many electrons have been lost or gained as electrons have a relative charge of -1.
Ionic compound
A compound made up of anions and cations, held together by ionic bonds, which arise due to the electrostatic attraction between oppositely charged ions. These structures are neutral overall.
Ionic radius
The radius of an ion. It is the distance between the nucleus and the outermost electron of the ion.
Isoelectronic ions
Refers to two atoms or ions that have the same electron configuration and the same number of valence electrons. These species often have similar chemical properties. For example, Ca 2+ and Mg +.
Metallic bonding
Strong electrostatic attraction between positive metal ions and the sea of delocalised electrons that surround them.
Polar bond
A covalent bond between two atoms in which the electrons in the bond are unevenly distributed. This causes a slight charge difference, inducing a dipole in the molecule.
Polar molecule
A molecule in which the electrons are not evenly distributed between the bonding atoms. The molecule is said to have a dipole.
