[Chemistry Form 4] Atom

The word 'atom' comes from a Greek word that means 'something that invisible'. However, atom can be split!

According to modern atomic theory, subatomic particles like protons and neutrons form the nucleus of an atom, while electrons whirl around the nucleus in different orbits with such a tremendous speed that they seem to form layers of shells around it.

Scientist And His Findings

John Dalton (1766 - 1844)
i) All elements are made up small indivisible particles called atoms.
ii) The atoms of an element are alike but differ from those of other elements.

J.J. Thompson (1856 - 1940)
Suggested the the atom is positively charged sphere with electrons embedded in it.

Ernest Rutherfold (1871 - 1937)
Discovered protons, and suggested thet protons are concentrated in the nucleus - the centre of an atom - which is surrounded by a cloud of electrons.

Niels Bohrs (1885 - 1962)
Proposed that electrons are arranged in orbits surrounding the nucleus.

James Chadwick (1891 - 1974)
Discovered neutrons, and proposed that the nucleus contains protons and neutrons, with electrons moving in orbit surrounding it.