Basic Chemistry - Atomic Structure

An atom is the smallest thing we could possibly use in science. An atom is the smallest because it is indivisible. If you picture a football stadium, the football on the pitch would be the nucleus, and a flying insect would be an electron. This gives a fairly reasonable representation of an atom's structure. However an atom is not the size of a football stadium! An atom is actually one Angstrom in diameter which is approximately one fifth of a millimetre.


Within the nucleus there are neutrons and protons. Atomic number is the number of protons within the nucleus. Mass number (atomic weight) is the number of protons and neutrons within the nucleus. If the number of neutrons within a nucleus changes then an isotope is formed. For example, carbon has different isotopes: (C-12 normal, six protons and six neutrons), C-13 (six protons and seven neutrons) and C-14 (six protons and eight neutrons. C-14 isotope is radioactive and has a half life and can be used to date various artefacts.

Electrons circulate in different orbitals around the nucleus. In the first shell of electrons up to two electrons can occupy the shell. In the second and following shells there can be up to eight electrons, this is in accordance with the octet rule. If a shell is full of electrons it is known as a valence shell. If the outermost shell is full of electrons then it is more stable, if the shell is not full, then the atom is likely to want to fill up with electrons and bond with other atoms. In this new molecule, the atoms are sharing electrons.