# 1.5.1 Using ions to explore atomic structure

Introducing you to ions at this point provides an opportunity to look back at section 1.1 and revisit that rather remarkable statement about the structure of an atom; ‘an atom is mainly empty space’.

Around 1910, Ernest Rutherford, a physicist working at the University of Manchester carried out an experiment where he fired positively charged helium ions (known as alpha particles) through sheets of gold foil approximately 10 000 atoms thick. Most of the particles passed straight through, with at most only a small deflection. However there were occasional instances of alpha particles rebounding right back from whence they came.

How does this observation support the picture of the atom described in section 1.1?

### Answer

Remember that alpha particles are positively charged; any deflection would be due to interaction with other positive charges. The beams that occasionally bounced back suggest there is a concentrated centre of positive charge – the nucleus. And as most alpha particles passed through the foil, this supports the idea that ‘an atom is mainly empty space’.

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