Programme 17: Atomic Structure

Programme Outline

The programme is divided into three parts:

17.1 Atomic Structure
17.2 Atomic Number and Mass Number
17.3 Electron Structure

17.1 Atomic Structure

This section of the programme takes a historical look at how the current picture of an atom developed. It begins by repeating J J Thompson’s early observations of electrons (cathode rays) and then models Rutherford’s alpha-particle scattering experiment using snooker balls and marbles. The section concludes by showing a simple orbital picture of the atom including the charge on an electron, proton and neutron.

17.2 Atomic Number and Mass Number

Taking the periodic table as a starting point, this section explains the terms atomic number and mass number in relation to the number of protons and neutrons in an atom. It uses a series of animations to show how the atomic number and mass number of the elements hydrogen, helium and lithium can be worked out and written down.

17.3 Electron Structure

Electrons moving around the outside of an atom occupy a series of shells at different distances from the nucleus. This orbital picture is modelled on screen using a series of ice hockey players moving around a set of rings drawn on an ice rink. The players illustrate how the first three shells can hold a fixed number of electrons (2.8.8) and how they fill up starting with the shell closest to the nucleus. After a number of examples, including fluorine, neon and sodium, the electron arrangement of the first 18 elements is overlaid on a periodic table. The electron arrangement of each atom is then related to its position in the table.