history of the atom

Who are the scientists that contributed to discovering the atom?

1. Democritus
2. John Dalton
3. J.J. Thompson
4. Ernest Rutherford
5. Niels Bohr
6. James Chadwick

How did Democritus contibute to discovering the atom?

Democritus (c. 500 B.C.)
Democritus proposed that all matter is made up of tiny, indivisible particles called atoms. He believed these atoms were eternal, indestructible, and separated by empty space.

How did John Dalton contibute to discovering the atom?

John Dalton (Early 1800s)
He described atoms as solid, indivisible spheres and proposed that:

How did J.J Thompson contibute to discovering the atom?

J.J. Thomson (1897)
J.J. Thompson constructed the 'plum pudding model'. He discovered electrons by carrying out a series of experiments, where he concluded that there couldn't just be 'solid spheres' and there must have contained negatively charged particles as well. He proposed that an atom was a ball of positive charge with electrons.

How did Ernest Rutherford contibute to discovering the atom?

Ernest Rutherford (1909)
Rutherford conducted the gold foil experiment, where alpha particles were fired at a thin sheet of gold. Most passed through, but some were deflected, suggesting a dense, positively charged nucleus at the atom's center. He proposed the 'nuclear model' with electrons surrounding this nucleus. However, this would mean the electrons would spiral into the nucleus.

How did Niels Bohr contibute to discovering the atom?

Niels Bohr (1913)
Niels Bohr suggested a solution to this problem, concluding that electrons orbitted the nucleus in shells like the planets orbit the sun. The orbiting of electrons prevents atoms from spiraling into the nucleus.

How did Ernest Rutherford contibute to discovering the atom later on?

Ernest Rutherford (Later on)
Rutherford later discovered that the positive charge of the nucleus is due to smaller particles called protons.

How did James Chadwick contibute to discovering the atom?

James Chadwick (1932)
Chadwick discovered the neutron — a neutrally charged particle in the nucleus — which explained the missing mass in atoms and contributed to the understanding of nuclear structure.