Atomic Structure


Atomic Structure > Introduction



In this module you will explore the basic structure of the atom, find out about isotopes, mass spectrometers and the arrangement of electrons in the atom



The Atom


The word atom comes from the Greek word ‘atomos’, which means ‘indivisible’.


It was Democritus, a Greek philosopher, who in 460 BC first came up with the idea of atoms. Democritus hypothesized that if you break a piece of matter in half and half again and half again and half again and so on, will you be able to break it forever or will you reach a point where you can break it no further. Democritus thought that you would reach a point where you could not break up the matter into anything smaller – i.e., at some point you would reach an atom.


Unfortunately for Democritus other Greek philosophers, including the influential Aristotle, rebuffed his ideas. For more than 2000 years, nobody did anything to take these thoughts forward.


The work of John Dalton in the 1800’s pointed to matter being made of elementary particles (atoms) and in 1897 John Joseph Thompson discovered the electron and proposed a model for an atom that involved sub atomic particles (often referred to as the ‘plum pudding model’).


Until the turn of the 20th century it was believed that the atom was the smallest indivisible unit in nature. However, thanks to the work of Planck, Rutherford, Bohr, Pauli, de Broglie, Schrödinger, Chadwick and Moseley a more detailed understanding of the atom was evolved and evidence generated from these scientists work led to a belief that the atom was made of smaller, sub atomic particles.


The work of these scientists is a great example of internationalism in science. Planck was German, Rutherford a New Zealander, Bohr was Danish, Pauli and Schrödinger were Austrian, Chadwick and Moseley were British, and be Broglie was French.


The major discoveries they made started around the end of the 19th century up until the mid third of the 20th century. This corresponded to great advances in society with regards to communication and transport. It allowed scientists from places that were once distant to read about and get together to discuss each other’s work much more often than they had been able to do previously.

Atoms are also very very small. An average atom will have a diameter of around 0.1 nanometers  (1 x 10-9 m) or 100 picometers. Approximately 7.5 trillion (7.5 x 10 12 ) would fit into the full stop (or period) that makes up this exclamation mark!