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Discovery of the Atom

100 years of Ernest Rutherford’s Theory of the Atom

Ernest Rutherford was born in New Zealand in 1871. From an early age he demonstrated an extraordinary aptitude for science. He won a place at Cambridge in 1895 and was appointed professor of physics at McGill, Canada, just three years later, aged 27. In 1908 he received the Nobel Prize for chemistry and his work on radioactivity.

Rutherford’s most significant discovery was not in chemistry, but in the field of physics, when he formulated a correct model of the atom. His work began when, after watching alpha particles being fired at a thin sheet of gold, he noticed that while many passed through, some of the particles were deflected. Findings of further experiments were published in 1909, but without a working explanation little attention was paid.

On 7 March 1911, Rutherford spoke at a meeting of the Manchester Literary and Philosophical Society, formally proposing that atoms have space within them, and that this explained why most of the particles passed through and some did not.

His theory is one that is maintained today, and it opened up the then-new discipline of nuclear physics.

What does Rutherford’s atom look like?

Departing from a previous ‘plum pudding’ model of the atom, in which negative electrons were embedded in a positive sphere, Ernest Rutherford proposed that the electrons surrounded a central nucleus. The incredibly dense nucleus has been likened to ‘a fly in a cathedral’ but despite its size relative to the whole of the atom, it makes up the majority of the mass.

The nucleus is surrounded by larger electrons that move around, meaning that most of the atom is actually empty space. Physicist Marcus Chown has suggested that if the space in atoms were removed, then the population of the world would fit into an area the size of a sugar cube.

Why is it important?

Atoms make up everything around us, from solid rock to oxygen, and Rutherford was the first person to correctly identify how they are structured. In describing the make-up of the atom, the reasons as to why some materials are more reactive than others became explainable due to differing amounts of electrons in an atom’s ‘shell’.

Rutherford later worked out how to artificially ‘split the atom’ by knocking positively charged protons from the nucleus, a process that was carried out in 1932 by another two of his colleagues using the world’s first particle accelerator.

The largest particle accelerator in the world today is in the CERN laboratory in Switzerland. The Large Hadron Collider accelerates atoms around the 27 km circumference of an underground tunnel in order to create collisions and examine even smaller fragments of matter.

Despite his distaste for honours, Rutherford has had several buildings named after him as well as the element Rutherfordium, number 104 on the Periodic Table. Eleven of Rutherford’s students went on to win a Nobel Prize.

Watch Discovery of an Atom to find out more about Ernest Rutherford's discovery.