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3. Splitting atoms page 9
Atoms losing bits
The electrons that whiz about outside the nucleus have a negative charge. They are held in the atom by the positive charge of the nucleus. This electrostatic attraction is part of one of the basic forces of nature – electromagnetism.

Interactive atom becoming an ion
Picture 3.1 A neutral atom that loses an electron becomes a positive ion.
Neutral atoms
In ordinary matter, the number of electrons in an atom is the same as the number of protons. The positive and negative charges balance each other. Overall, the atom is uncharged (neutral).

However, if something happens to make an atom lose or gain an electron then the atom will no longer be neutral.

Atoms or ions
An atom that gains or loses an electron becomes an ion. If it gains a negative electron, it becomes a negative ion. If it loses an electron it becomes a positive ion (see page 10 for more on ions).

When a whole group of atoms (usually as part of an insulator) gain or lose electrons, this will cause static electricity (see page 11 for more on electrostatics).

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Question 8
Look at the numbers of particles in the atoms below. In each case, decide whether the atom is neutral or charged. In the last four, you will need to say whether it has become an ion and what the net charge is.
elements protons electrons
sodium 11 11
sodium 11 10
oxygen 8 9
oxygen 8 8
iron 26 24
iron 26 23
hydrogen 1 0
hydrogen 1 1