Summary Atoms

Atoms are very small, having a radius of about 1x10 -10 metres. The basic structure of an atom is a
positive charged nucleus composed of both protons and neutrons surrounded by negatively charged
electrons.

Protons on the inside of the nucleus and have a charge of +1

Electron on the outside of the nucleus have a charge -1

Neutron on the inside of the nucleus and have a charge of 0

Atomic mass- the number of protons and neutrons in the nucleus.(Atomic mass-Atomic number)

Atomic number- the number of just protons and electrons in the nucleus

Ionisation is the addition or removal of an electron to create an ION.

 Losing an electron creates a positive ION.
 Gaining an electron creates a negative ION.

Isotopes of an element are atoms with the same number of protons(same atomic number) but
different number of neutrons(mass number). E.g.




(Study all page 3,4 and 5)

There could be 3 things wrong with the nuclei of unstable elements:

 The nuclei could be too big
 The nuclei could have too much energy

Henri Becquerel

Bq- becqerels

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(study the table on page 7)

Radioactive decay is when an unstable nucleus loses energy by realising radiation

Alpha particle:

 Mass number decreases by 4 and atomic number decreases by 2
 Add +42a at the end of the equation
 It can be stopped by paper

Beta particle:

 Mass number stays the same and atomic number increases by 1
 Add +0-1b at the end of the equation
 It cannot be stopped by paper and it can be stopped by aluminium

Gamma ray: