The structure of an atom

Atoms are very small, having a radius of about 1 × 10⁻¹⁰ metres.

The basic structure of an atom is a positively charged nucleus composed of both protons and neutrons surrounded by negatively charged electrons.

The radius of a nucleus is less than 1/10 000 of the radius of an atom. Most of the mass of an atom is concentrated in the nucleus.

The electrons are arranged at different distances from the nucleus (different energy levels). The electron arrangements may change with the absorption of electromagnetic radiation (move further from the nucleus; a higher energy level) or by the emission of electromagnetic radiation (move closer to the nucleus; a lower energy level).

MS 1b

WS 4.4

Students should be able to recognise expressions given in standard form.