10CHE8 - Unit 1 (The Element of Surprise) and Unit 3 (Ocean Chemistry) Definition

Atom

The smallest particle of an element that retains its identity in a chemical reaction.

Molecule

A neutral group of non-metal atoms covalently bonded.

Element

A substance that is made up of one type of atom, defined by its atomic number.

Compound

A substance that is made up of atoms of different elements joined together by chemical bonds in a fixed ratio.

Atomic number

The number of protons in the nucleus of an atom of an element.

Mass number

The total number of protons and neutrons in the nucleus of an atom.

Ion

An atom or molecule that has gained or lost one or more electrons and is charged.

Polyatomic ion

A tightly bound group of atoms that behaves as a unit and has a positive or negative charge.

Ionic bond

Involves the electrostatic attraction between positively and negatively charged ions, often formed through electron transfer.

Covalent bond

Involve sharing electrons between non-metal atoms to form discrete molecules.

Metallic bond

Involves the delocalisation of valence electrons from the outer energy level of metal atoms, causing metal cations to form and float around in a ‘sea’ of delocalised electrons

Precipitate

An insoluble solid formed when two soluble ionic solutions react.

acid

a substance which dissociates to form hydrogen ions in a solution. (a proton donor)

base

a substance which reacts with an acid to form a salt and water only. 

alkalis

a soluble base, which in solution, produces hydroxide ions (OH^-).