GLOSSARY AS CHEM

Atom

The smallest unit of a chemical element. There are 117 known elements, so 117 different kinds of atom.

Nanometre

1nm = 1e-9 (atoms are typically 01nm in diameter)

Mass spectrometer

An instrument that can accurately measure the masses of atoms and molecules and their abundance.

Abundance

How plentiful %

Relative atomic mass

The weighted average mass of an atom relative to the mass of an atom of carbon-12 whose mass is 12 units.

Relative isotopic mass

The mass of an atom of an isotope compared with the mass of an atom of the carbon-12 isotope whose mass is 12 units

1st ionisation energy

The energy required to remove the outer electron from a mole of gaseous atoms to produce 1 mole of positive gaseous ions, each with a charge of 1+

Electron configuration

A way of representing the electron arrangement in an atom or ion.

Orbital

The region around the nucleus that can hold up to 2 electrons with opposite spin

Molecule

A specified number of atoms that are covalently bonded together

Covalent bond

Electrostatic attraction between a shared pair of electrons between 2 metal atoms and the nuclei of those atoms

Dative covalent bond

A covalent bond where both electrons being shared originate from the same atom

Lone pair

Two electrons in the same orbital which are currently not involved in forming bonds

Electron pair repulsion theory

Theory used to explain the shape and bond angles of molecules. The shape is determined by how many bonding and non-bonding pairs there are around the central atom. They repel and move to positions that dictate the shape.

Electronegativity

A measure of how strongly a pair of electrons in a covalent bond is attracted to an atomic nucleus. Fluorine is the most electronegative.

Polar

Differences in electronegativity between atoms when there is an uneven distribution of electrons

Electric dipole

A separation of opposite electrical charges. A polar molecule will always have a permanent electric dipole

Permanent dipole-dipole attraction

Intermolecular force between polar molecules

Hydrogen bond

Dipole-dipole attraction that is strong due to the electropositive atom (H) being attracted to a lone pair of electrons on the electronegative atom