Element: definition in chemistry
Element: A pure substance made of only one kind of atom, defined by the number of protons in its nucleus (its atomic number).
Elements are the simplest substances and cannot be broken down into anything simpler by chemical reactions. Every atom of an element has the same number of protons, although the number of neutrons can differ between isotopes. Of the 118 known elements, 94 occur naturally on Earth, some only in tiny traces, and the rest have been made in laboratories.
Examples
- Oxygen (O) — atomic number 8
- Gold (Au) — atomic number 79
- Carbon (C) — found as both graphite and diamond
- Helium (He) — a noble gas used in balloons
On the periodic table
Every box on the periodic table is one element, and the boxes are arranged in order of increasing atomic number.