Element – IGCSE Chemistry Definition

An element is the simplest type of pure substance. The 0620 syllabus requires you to define element, distinguish it from compounds and mixtures, know element symbols, and classify elements as metals or non-metals. Element identification runs through the entire course, from atomic structure to organic chemistry.

The 0620 definition

An element is a substance that contains only one type of atom and cannot be broken down into simpler substances by chemical methods.

All atoms of a given element have the same number of protons (the same atomic number). This is what defines the element.

Elements on the periodic table

The periodic table arranges all known elements by increasing atomic number. Each element has:

• A name (e.g. sodium)
• A symbol — one or two letters, first letter capitalised (e.g. Na)
• A unique atomic number

Symbol	Element	Classification
H	Hydrogen	Non-metal
C	Carbon	Non-metal
O	Oxygen	Non-metal
Na	Sodium	Metal
Fe	Iron	Metal
Cu	Copper	Metal
Cl	Chlorine	Non-metal
Br	Bromine	Non-metal

Metals vs non-metals

Property	Metals	Non-metals
Appearance	Shiny (lustrous)	Dull (except diamond, graphite)
State at room temperature	Mostly solid (except mercury)	Solid, liquid, or gas
Conductivity	Good conductors of heat and electricity	Poor conductors (except graphite)
Malleability	Malleable and ductile	Brittle (if solid)
Bonding tendency	Lose electrons, form positive ions	Gain or share electrons
Position on periodic table	Left and centre	Right side

Elements can exist as atoms or molecules

Some non-metal elements exist as molecules. For example, oxygen exists as O₂ (two oxygen atoms covalently bonded). It is still an element because it contains only one type of atom. The common diatomic elements to remember: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂.

Worked exam question

State whether each of the following is an element, compound, or mixture: (a) O₂ (b) CO₂ (c) air (3)

Mark scheme

(a) Element [1] — contains only one type of atom (oxygen)

(b) Compound [1] — contains two types of atom (carbon and oxygen) chemically bonded

(c) Mixture [1] — contains different substances (nitrogen, oxygen, etc.) not chemically bonded

Common exam mistakes

• Calling O₂ a compound because it contains two atoms. It is an element — both atoms are the same type (oxygen). A compound requires two or more different elements chemically combined.
• Confusing element symbols — CO (carbon monoxide, a compound) vs Co (cobalt, an element). Capitalisation matters.
• Saying an element “cannot be broken down at all”. The correct phrase is “cannot be broken down by chemical methods”. Nuclear reactions can change elements, but this is outside the 0620 syllabus.