Chemical element

A chemical element is a substance that is made up of only one type of atom.^[2] Atoms are made up of protons, neutrons, and electrons.

The number of protons in an atom is called the atomic number. For example, all atoms with 6 protons are atoms of the chemical element carbon, and all atoms with 92 protons are atoms of the element uranium. The number of neutrons in the nucleus does not have to be the same in every atom of an element. Atoms of the same element with different numbers of neutrons are called isotopes. Saying that a substance "contains only one type of atom" really means that it contains only atoms that all have the same number of protons.

The number of protons in the nucleus causes its electric charge. This fixes the number of electrons in its normal (un-ionized) state. The electrons in their atomic orbitals determine the element's various chemical properties.

Elements are the basic building blocks for all types of substances. If a substance contains more than one type of atom, it is a compound or a mixture. The smallest particle of a compound is a molecule.

118 different chemical elements are known to modern chemistry. 92 of these elements can be found in nature,^[1] and the others can only be made in laboratories. The human body is made up of 26 elements.^[1] The last natural element discovered was uranium, in 1789.^[3][4] The first man-made element was technetium, in 1937.

Chemical elements are commonly arranged in the periodic table. Where the elements are in the table tells us about their properties relative to the other elements.

1. ↑ ^{1.0 1.1 1.2} Ryan, Lawrie (2001). Chemistry for You: National Curriculum Edition for GCSE (2 ed.). Nelson Thornes. ISBN 9780748762347.
2. ↑ Cite error: The named reference brand was used but no text was provided for refs named (see the help page).
3. ↑ Devlin, Jacinta; Cochrane, Helen (2005). "1". Science Links 2. Coffey, Rhonda (VELS ed.). Heinemann. p. 5. ISBN 1740815203.
4. ↑ "Periodic Table: Uranium". Chemical Elements.com. Retrieved 2011-03-22.