Our world is made of elements and combinations of elements called compounds. An element is a pure substance made of atoms that are all of the same type. At present, 116 elements are known, and only about 90 of these occur naturally.
Elements and the ‘Big Bang’ theory
During the formation of the universe some 14 billion years ago in the so-called ‘Big Bang’, only the lightest elements were formed – hydrogen and helium along with trace amounts of lithium and beryllium. As the cloud of cosmic dust and gases from the Big Bang cooled, stars formed, and these then grouped together to form galaxies.
The other 86 elements found in nature were created in nuclear reactions in these stars and in huge stellar explosions known as supernovae.
Elements and our Sun
For most of their lives, stars fuse elemental hydrogen into helium in their cores. Two atoms of hydrogen are combined in a series of steps to create helium-4. These reactions account for 85% of the Sun’s energy. The remaining 15% comes from reactions that produce the elements beryllium and lithium.
The energy from these nuclear reactions is emitted in various forms of radiation such as ultraviolet light, X-rays, visible light, infrared rays, microwaves and radio waves. In addition, energised particles such as neutrinos and protons are released, and it is these that make up the solar wind.
Earth is in the path of this energy stream, which warms the planet, drives weather and provides energy for life. The Earth’s atmosphere is able to screen out most of the harmful radiation, and the Earth’s magnetic field can deflect the harmful effects of the solar wind.
When a star’s core runs out of hydrogen, the star begins to die out. The dying star expands into a red giant, and this now begins to manufacture carbon atoms by fusing helium atoms.
More massive stars begin a further series of nuclear burning or reaction stages. The elements formed in these stages range from oxygen through to iron.
During a supernova, the star releases very large amounts of energy as well as neutrons, which allows elements heavier than iron, such as uranium and gold, to be produced. In the supernova explosion, all of these elements are expelled out into space.
Our world is literally made up of elements formed deep within the cores of stars now long dead. As Britain’s Astronomer Royal Sir Martin Rees said, “We are literally the ashes of long dead stars.” When you buy a party balloon that floats in air, it is filled with helium gas – most of which was created when the universe was only 3 minutes old!
Examples of element making (nucleogenesis) in helium burning reactions:
- 3 helium atoms fusing to give a carbon atom: 3 @ 4He → 12C
- carbon atom + helium atom fusing to give an oxygen atom: 12C + 4He → 16O
- oxygen atom + helium atom fusing to give a neon atom: 16O + 4He → 20Ne
- neon atom + helium atom fusing to give a magnesium atom: 20Ne + 4He → 24Mg
Only 90 of the 116 known elements occur naturally, so where have the other 26 come from?
The answer is to be found in the development of nuclear power plants and machines known as particle accelerators:
- Scientists discovered that, by allowing fast neutrons to collide with the common isotope of uranium known as U-238 in a nuclear reactor, the ‘new’ element plutonium was made.
- By smashing atoms together in machines known as particle accelerators, it was discovered that new elements could be made. For example, bombarding atoms of the element curium with atoms of neon made element 106 – seaborgium.
Nature of science
One of the habits of scientists is open-mindedness. Scientists need to be receptive to new ideas and suggestions. As new evidence is discovered, new ways of interpreting and understanding it may have to be considered.