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Dalton
John Dalton created the very first atomic theory.
Dalton viewed atoms as tiny, solid balls.
His atomic theory had 4 statements…
1. Atoms are tiny, invisible particles.
2. Atoms of one element are all the same.
3. Atoms of different elements are different.
4. Compounds form by combining atoms. -
JJ Thomson
J.J. Thomson discovered electrons.
He also proposed the existence of a (+) particle…
model was known as the “raisin bun model”…
(Atoms are made mostly out of (+)
charged material, like dough in a bun.
The (-) charged electrons are
found inside the (+) dough.) -
Ernest Rutherford
Rutherford discovered protons and the nucleus.
He showed that atoms have (+) particles in the center, and are mostly empty space.
He called these (+) particles protons.
He called the center of atoms the nucleus.
Most particles went
right through!
Strangely, some
particles are deflected
(He called these (+) particles protons.
He called the center
Radioactive material
emits beam of (+) alpha
particles
of atoms the nucleus.) -
Niels Bohr
Niels Bohr improved on Rutherford’s model.
Every atom has a specific number of electron shells. -
James Chadwick
Chadwick discovered neutrons.
He called these particles neutrons.
Working with Rutherford, he discovered particles with no charge.Neutrons are also found in the nucleus. -
Modern
Work done since 1920 has changed the model. The new atomic model has electrons moving around the nucleus in a cloud. It is impossible to know where an electron is at any given time.
