What Is an Element? Simple Definition, Types, and Examples

You’ve probably seen the periodic table in a classroom, but what defines a chemical element? Today, scientists recognize 118 known elements, each defined by the number of protons in its nucleus (IUPAC — the international authority on chemical nomenclature).

Number of known chemical elements: 118 ·
Number of naturally occurring elements: 94 ·
Year the modern periodic table was created: 1869 ·
Smallest particle maintaining element identity: Atom ·
Simplest definition property: Cannot be broken down into simpler substances

Five essential data points about the chemical elements, one pattern: the definition hinges on a single physical property — the number of protons in the nucleus.

What is a simple definition of an element?

Definition in plain language

An element is a pure substance that cannot be broken down into any other substance by chemical means (American Chemical Society). That means no heating, mixing, or dissolving will split it into something simpler. Each element consists of only one type of atom — the smallest unit that retains its identity.

Properties of an element

• All atoms of an element have the same number of protons (IUPAC).
• Elements can be metals, nonmetals, or metalloids.
• Physical properties (melting point, density, conductivity) differ widely across elements.

The implication: no matter how you treat a pure sample of gold, it stays gold — you cannot turn it into lead by ordinary chemistry.

How to explain elements to a kid?

Elements are like the letters of the alphabet. Just as letters combine to make words, elements combine to make compounds and all the substances around us. There are about 100 different elements that make up all matter on Earth (American Chemical Society).

What best defines an element?

The two-part definition: an element is a substance made of one type of atom, and it cannot be broken down into simpler substances by ordinary chemical processes. All atoms of an element share the same number of protons (IUPAC).

What is an element in chemistry?

Chemical element definition

A chemical element is defined by the number of protons in its atomic nucleus — a value called the atomic number (IUPAC — periodic table reference). This is the single criterion that separates elements from compounds and mixtures. The American Chemical Society states that elements are the building blocks of all matter on the periodic table.

Atomic number and identity

• Hydrogen: atomic number 1 → one proton
• Carbon: atomic number 6 → six protons
• Oxygen: atomic number 8 → eight protons

If the number of protons changes, the element changes. That’s why nuclear reactions (which alter the nucleus) can transform one element into another — but ordinary chemical reactions cannot.

The pattern: The periodic table organizes these 118 substances by increasing atomic number, grouping them into families with similar chemical behavior (American Chemical Society). Groups 1, 2, 17, and 18 are among the best-known families.

What are some examples of elements?

Common element examples: hydrogen, oxygen, carbon, gold

• Hydrogen (H) — the lightest element, atomic number 1. Makes up about 75% of the universe’s mass.
• Carbon (C) — atomic number 6. Backbone of organic chemistry and all known life.
• Oxygen (O) — atomic number 8. Essential for respiration; about 21% of Earth’s atmosphere.
• Gold (Au) — atomic number 79. Dense, malleable, and does not tarnish.

Examples of elements vs. compounds

Elements are the raw ingredients; compounds are combinations. Water (H₂O) is a compound made of two elements: hydrogen and oxygen. You can separate water into hydrogen and oxygen by electrolysis — but you cannot split a single atom of hydrogen into anything simpler (American Chemical Society).

The trade-off: elements are boring on their own — most reactivity comes from how they combine. The fun begins when elements bond to form compounds with entirely new properties.

Key scientific perspectives

“A chemical element is a substance that cannot be broken down into simpler substances by ordinary chemical reactions.”

— Royal Society of Chemistry — the UK’s professional chemistry body

“The atomic number — the number of protons in the nucleus — is the fundamental property that identifies an element.”

— Henry Moseley, 1913, as cited by Encyclopaedia Britannica

For students learning chemistry, the choice is clear: define every element by its atomic number. The periodic table is not just a list of symbols — it’s a map of proton counts, and that single number unlocks the identity of all matter. For teachers, the implication is straightforward: when a student asks “what is an element?”, the shortest honest answer is “a substance made of atoms that all have the same number of protons.”

For a deeper look into the fundamental building blocks of matter, read our detailed guide on chemical elements and their properties.

Frequently asked questions