P2.5.1 - AQA GCSE Physics Unit 2

P2.5.1	Atomic structure
	a) The basic structure of an atom is a small central nucleus composed of protons and neutrons surrounded by electrons.	Candidates should appreciate the relative size of the nucleus compared to the size of the atom. An explanation of this is given on the link page The diagram summarises all of these points.
	b) The relative masses and relative electric charges of protons, neutrons and electrons.
	c) In an atom the number of electrons is equal to the number of protons in the nucleus. The atom has no overall electrical charge.
	d) Atoms may lose or gain electrons to form charged particles called ions.
	e) The atoms of an element always have the same number of protons, but have a different number of neutrons for each isotope. The total number of protons in an atom is called its atomic number. The total number of protons plus neutrons in an atom is called its mass number.	These are *definitions* - learn them!