The New Alchemy: Rutherford and the Atom

RutherfordErnest Rutherford FRS

What is the world made of?

Philosophers and scientists have tried to answer this question for centuries. In 1911 Ernest Rutherford FRS made an important leap forward, unveiling an atomic model in which electrons orbit a central nucleus. This online exhibition celebrates Rutherford's achievements and traces the history of the atom from the ancient world to the sub-atomic age.

Ancient atomism

Ancient Greek, Roman and Hindu philosophers suggested that the universe consisted of tiny indivisible particles atoms. Atoms were unchangeable and moved constantly through space.

Aristotle, however, believed matter had four fundamental properties wet, dry, hot, and cold and that all earthly substances were composed of four 'elements', water, earth, fire, and air.

Aristotle's view was very influential in Europe throughout the middle ages and persisted into the seventeenth century. People speculated that matter might be transformed from one type (hot and dry, for example) to another (hot and wet). This theory underpinned the practice of alchemy.

Alchemy

Alchemy meant much more than the search for the Philosopher's Stone (a mystical substance that transmuted metals into gold and cured all diseases). Alchemy was supposed to bring its practitioners closer to spiritual perfection and give them a secret understanding of the universe.

However in some respects it is difficult to distinguish between alchemy and early chemistry. Alchemists used metallurgical techniques and developed new equipment, such as more efficient furnaces. Alchemical experiments conducted on different substances could lead to important discoveries for example, in 1669 the German alchemist Hennig Brand discovered the element phosphorus while working with a solution of urine.
Robert Boyle and Sir Isaac Newton, two of the leading scientists in seventeenth-century England, were both very interested in alchemy.

Read more about Alchemy

Elements and compounds

In 1808 the Manchester-based scientist John Dalton FRS published A New System of Chemical Philosophy, in which he outlined his theories about elements and atoms. He proposed several groundbreaking ideas: that each element is composed of atoms identical to the other atoms in that element; that atoms of one element combine with atoms of another element to form compounds; and that the atoms of each element are characterised by their weight, which can be calculated by systematic analysis.
Dalton also proposed a system of pictorial representations of different atoms. However it was difficult to use and the system of alphabetical notation used by the Swedish chemist Berzelius was later adopted universally (eg. 'H2O'). Dalton was often invited to lecture on his theories, and he used a set of small wooden balls with holes and spokes to illustrate the combination of elements.

Read more about Elements and compounds

The 'plum pudding' atom

Around 1875 the British physicist William Crookes FRS experimented with a new piece of equipment. It consisted of an evacuated glass cylinder with metal electrodes at either end. When a high voltage was applied, electrons travelled in straight lines from the cathode to the anode. However they had so much momentum that many flew past the anode, hitting the end wall of the tube and causing it to glow. The stream of electrons was called a cathode ray.

In 1896 J J Thomson, working with colleagues at the Cavendish Laboratory in Cambridge, performed experiments showing that cathode rays were not waves, molecules or atoms, but unique particles. He called them 'corpuscles', and showed that they were about a thousand times less massive than the smallest atom. In 1904 Thomson proposed a model of the atom in which these corpuscles (now called electrons) were 'enclosed in a sphere of uniform positive electrification'. This was later dubbed the plum pudding model.

Read more about the 'plum pudding' atom

Ernest Rutherford FRS

Born in 1871 near Nelson in the South Island of New Zealand, Rutherford was the son of a flax miller. He was educated at the local grammar school, then won a scholarship that allowed him to attend Canterbury College in Christchurch. He studied mathematics and physics, discovering a talent and enthusiasm for experiment. This would characterise his whole research career.

In 1895 Rutherford moved to Cambridge to work at the Cavendish Laboratory with J J Thomson. He worked on newly-discovered x-rays and radioactivity, the exciting phenomena of the day. It was while at McGill University in Montreal that Rutherford and Frederick Soddy FRS reached the startling conclusion that transmutation' occurs naturally in some elements. They had identified the processes of radioactive decay in radium and thorium. Rutherford jokingly warned Soddy, 'don't call it transmutation, they'll have our heads off as alchemists!'

Rutherford was awarded the 1908 Nobel prize in Chemistry for his work on radioactive decay. At the University of Manchester he collaborated with Hans Geiger and an undergraduate student, Ernest Marsden, on an experiment in which a thin piece of gold foil was bombarded with alpha particles. Surprisingly, some particles bounced back. The results suggested to Rutherford that the atom consisted of a small positively-charged nucleus orbited by electrons. His model was revised by Niels Bohr in 1913 but remained an important breakthrough in the understanding of atomic structure.

Read more about Ernest Rutherford FRS

New theories of the atom

The ground-breaking work of Rutherford and his collaborators launched the new field of nuclear physics. Following his lead, researchers such as James Chadwick FRS and Patrick Blackett FRS delved further into the structure of the atom. In 1932, Chadwick announced the existence of the neutron. Physicists and others became interested in the potential use of atomic energy. Worldwide curiosity about CERN's newly-constructed Large Hadron Collider demonstrates that our fascination with the tiniest particles of the natural world continues.

Read more about new theories of the atom

Acknowledgements

The Royal Society would like to thank the following people and institutions for their help in organising this exhibition.

Ms Terri Elder

University of Canterbury, Christchurch, New Zealand

Prof. Mary Fowler

Mr Joshua Nall

The Whipple Museum for the History of Science, Cambridge

Ms Catherine Rushmore

Museum of Science and Industry, Manchester

Prof. Ken Strongman

University of Canterbury, Christchurch, New Zealand

Dr Gordon Squires

Cavendish Laboratory, University of Cambridge

Events and exhibitions

We run a programme of regular events, conferences and exhibitions on the history of science for researchers and members of the public.

Audio recordings and video recordings are available for many of our events.

An archive of some of our past exhibitions is also available.