This resource provides explanations of the key concepts encountered when exploring the elements – the building blocks of our universe. This covers the ‘basics’ that every student should understand.

Big Bang theory

A cosmological theory holding that the universe originated approximately 14 billion years ago from the violent explosion of a very small agglomeration of matter of extremely high density and temperature.

Chemical element

A chemical element (or element) is a material that cannot be decomposed by chemical reaction into a simpler substance. Elements may be thought of as the basic chemical building blocks of matter.

Element formation

Deep within the cores of stars, nuclear fusion reactions take place that result in the production of elements other than hydrogen. This process is also known as nucleogenesis.


The smallest possible unit of matter that still maintains an element’s identity during chemical reactions. Atoms contain one or more protons and neutrons (except hydrogen (H), which normally contains no neutrons) in a nucleus around which one or more electrons move.

Periodic table

A tabular arrangement of the chemical elements based on increasing atomic number. Elements with similar properties fall into vertical columns called groups. For example, the noble gases (Group 18) are all chemically unreactive, whereas the alkali metals (Group 1) are all very chemically reactive.


Any of a category of elements that usually have a shiny surface, are generally good conductors of heat and electricity, and can be melted or fused, hammered into thin sheets, or drawn into wires, for example, copper.


A mixture of a metal element with one or more other elements. For example, the alloy brass is a mixture of copper and zinc. Titanium-based alloys, like Ti6V4Al, are being increasingly used in aerospace applications.


Atoms with the same atomic number but different mass numbers, due to differing numbers of neutrons. Some isotopes, like carbon-14, have unstable nuclei. They are known as radioisotopes and decay by spontaneous emission of energy and particles.


The time required for half of a given sample to undergo radioactive decay. Half-lives vary a lot. In the case of carbon-14, this time is 5,370 years, whereas with iodine-131, used in some forms of medical imaging, the half-life is 8 days.


The spontaneous emission of energy and particles from unstable atomic nuclei. When iodine-131 decays, it emits highly energetic electrons called beta particles along with gamma radiation.

    Published 30 September 2009