Element

In-depth explanation of Element

An element is a pure substance whose atoms all have the same atomic number, which is the count of protons in the nucleus. Because the proton count defines the element, changing it changes the element itself, which ordinary chemical reactions cannot do. Elements cannot be broken down into simpler substances by chemical means, although nuclear reactions can transform one element into another. About 118 elements are known, and roughly 90 of them occur naturally on Earth. Each element is represented by a one or two letter symbol, such as H, Fe or Au, derived from its English or Latin name.

Going deeper: Element

Key ideas: An element is defined by its atomic number Z, and about 118 are known, roughly 90 naturally occurring. Each has a one or two letter symbol with the first letter capitalized only (Co is cobalt, CO is carbon monoxide). Elements cannot be split into simpler substances by ordinary chemical reactions. Some exist as molecules, such as H2, N2, O2, P4 and S8.

Common mistakes and connections: Students confuse an atom of an element with a molecule of an element: O is one atom, O2 is a diatomic molecule. Element names versus symbols from Latin (Na, K, Fe, Pb) are another trap. Elements are organized by the periodic table and combine to form compounds.

Visualization of Element

Each element has its own atomic number and mass; here Li to Ne show the average atomic mass rising steadily with atomic number. The interactive lesson shows this as a live animation or chart.

Worked example and use case

All atoms with 8 protons are oxygen atoms, whether they are found in water, in rust or in air.

Where Element fits in Atomic Structure & Periodicity

Element is topic 3 of 115 in Atomic Structure & Periodicity.

Related topics

• MatterBeginner
• AtomBeginner
• CompoundBeginner
• MixtureBeginner
• Pure SubstanceBeginner

Browse all 115 topics in Atomic Structure & Periodicity