SACE Stage 1 Chemistry: Topic 3 - Molecules

Allotrope

Different structural forms of the same element in the same physical state (e.g.

Bonding Electrons

Electrons that are shared between atoms in a covalent bond.

Covalency

The number of covalent bonds an atom can form; determined by the number of electrons needed to complete its outer shell.

Covalent Bond

A chemical bond formed when two atoms share one or more pairs of electrons.

Covalent Layer Lattice

A structure in which atoms form strong covalent bonds in 2D layers

Covalent Molecular Lattice

A solid made of discrete molecules held together by weak intermolecular forces (e.g.

Covalent Network Lattice

A giant structure where atoms are bonded by strong covalent bonds in all directions (e.g.

Dipole

A molecule or bond in which there is an uneven distribution of charge due to differences in electronegativity

Dipole–Dipole Interaction

An intermolecular force between two polar molecules due to attraction between opposite partial charges.

Dispersion Force

A weak intermolecular force caused by temporary dipoles in molecules; present in all molecules

Electron Dot Formula

A representation of a molecule showing the valence electrons as dots around atoms and shared electron pairs as bonds.

Electronegativity

The ability of an atom to attract electrons in a chemical bond.

Hydrogen Bond

A strong type of dipole–dipole attraction between a hydrogen atom (bonded to N

Lone Pair

A pair of valence electrons on an atom that are not involved in bonding.

Non-bonding Electrons

Electrons in the valence shell that are not shared with another atom; another term for lone pairs.

Octet

A full outer shell of eight electrons

Polar Molecule

A molecule with an uneven distribution of charge due to asymmetrical shape and polar bonds that do not cancel out.

Polarised Bond

A covalent bond where the electron density is shifted toward the more electronegative atom

Semistructural Formula

A simplified representation of a molecule showing the order of atoms and some bonding information

Structural Formula

A diagram showing all the atoms and bonds in a molecule explicitly

Sublimes

The process by which a solid changes directly into a gas without passing through the liquid phase (e.g.

Valence Structure

A structural formula that shows bonding and non-bonding electrons in a molecule