8.1 - Matter

Atomic Substances, Molecular Substances and Ionic Substances

• Matter consists of tiny and discrete particles.
• Matter is formed by three types of particles: atoms, molecules and ions.

Particle	Definition
Atom	The smallest particle of an element; the most basic unit in an element.
Molecule	Two or more atoms which are chemically combined. The atoms may be of the same or different types.
Ion	A positively-charged or negatively-charged particle formed when an atom loses or gains electrons.

• An atom consists of the subatomic particles proton, neutron and electron.
• Substances are classified according to the type of particles they contain.

Type of substance	Particles and examples
Atomic substance	Contains atoms only. All metals and inert gases are made up of atoms. Examples: gold and helium.
Molecular substance	Contains molecules. Most non-metal substances exist as molecules. Examples: oxygen and water.
Ionic substance	Contains positive and negative ions formed through a reaction between a metal and a non-metal. Example: sodium chloride, which contains sodium ions and chloride ions.

Particle arrangement in atomic substances

• Metal: atoms are arranged closely in a neat and orderly manner.
• Inert gas: atoms are spread far apart with no regular arrangement.

Formation of molecular and ionic substances

• A reaction between non-metal elements forms a compound that exists as a molecular substance.
• A reaction between a metal element and a non-metal element forms an ionic substance.

Existence of Elements in Various Forms

• An element can exist in the form of an atom, molecule or ion.
• The same element can exist in different forms depending on the substance in which it is found.

Element	Forms
Iron	Exists as atoms in the head of a hammer; exists as ions in a rust compound.
Hydrogen	Exists as ions in lime juice; exists as molecules in air.

Classification examples

• Atoms: iron sheet, copper wire, helium gas.
• Molecules: ice cube, sugar cube, oxygen gas.
• Ions: common salt, marble, limewater.