Elements, Compounds and Mixtures

Definition of an Element:
An element is a substance which cannot be split into two or more simpler substances by chemical processes or by electricity
Elements can be classified into metals, non-metals and metalloids (elements that have properties of both metals and non-metals, eg. silicon)

Physical properties of metals and non metals

Metals	Non-metals
- Shiny appearance (lustrous)	- Dull appearance is solid (non-lustrous)
- Solids at r.t.p (except for mercury)	- Either gases, volatile liquids or solids with low melting points at r.t.p (except for carbon)
- Malleable (can be hammered into different shapes without breaking) - Sonorous (make a ringing sound when struck) - Ductile (can be drawn into wires)	- Brittle of solid (easily broken when hammered)
- High melting points and boiling points (except for sodium, potassium and mercury)	- Low melting points and boiling points (except for carbon and silicon)
- Good conductors of heat	- Poor conductors of heat (except carbon in the form of diamond and graphite)
- Good conductor of electricity in all states of matter	- Poor conductors of electricity (except carbon in the form of graphite)

Definition of a Compound:
A compound is a substance made up of two or more elements chemically combined together.

Definition of a Mixture:
A mixture consists of two or more substances which are not joined together chemically.

Definition of Ions:
An ion is a charged particle formed from an atom or a group of atoms by the loss or gain of electrons

Definition of Atoms:
Atoms are the smallest particles of an element that have the chemical properties of that element.

Definition of Molecules:
A molecule is a group of two or more atoms that are chemically combined/ joined together.

Diatomic: A combination of 2 atoms
eg. O2
Triatomic: Molecules consisting of 3 atoms
eg. O3
Polyatomic: A combination of 4 or more atoms
eg. Sp
Monatomic: Made up of one atom.
eg. He, Ar

Differences between a mixture and a compound

	Mixture	Compound
Separation	The components of a mixture can be separated by physical methods, eg. filtration, distillation or chromatography	The elements in a compound can only be separated by chemical reactions or by using electricity
Properties	The chemical properties of a mixture are the same as those of its components	The physical and chemical properties of a compound are different from those of the elements in the compound
Energy change	No chemical reaction takes place when a mixture is formed- usually there is little or no energy change	A chemical reaction takes place when a compound is formed- usually there is an energy change, eg. The reactants become hot
Composition	The components of a mixture can be mixed in any proportion	The elements in a compound are always combined in a fixed proportion (by mass)

Definition of an Alloy:
An alloy is an example of a mixture
An alloy is a mixture of of metals with other elements (usually metals but sometimes non-metals like carbon)
Alloys are widely used and in great demand as they tend to be stronger than pure metals