Timeline of the History of Atomic Theories
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Created byTara Guo
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Democritus'
Atomic TheoryHe proposed that everything in the world was made up of tiny
particles surrounded by empty space and he even speculated
that they vary in shape and size depending on the substance they compose.Dolton's
Solid sphere modelDalton drew upon the Ancient Greek idea of atoms (the word 'atom' comes from
the Greek 'atomos' meaning indivisible).His theory stated that atoms are indivisible,
those of a given element are identical, and compounds are combinations of different
types of atoms.J.J. Thomson's
Plum pudding modelThomson discovered electrons (which he called 'corpuscles") in atoms in 1897,
for which he won a Nobel Prize. He subsequently produced the 'plum pudding'
model of the atom. It shows the atom as composed of electrons scatterec
throughout a spherical cloud of positive chargeErnest Rutherford's
Nuclear MoldeRutherford fired positively charged alpha particles at a thin sheet of gold foil.
Most passed through with little deflection, but some deflected at large angles.
This was only possible if the atom was mostlv empty space,
ith the positive charge concentrated in the centre: the nucleusNiels Bohr's
Planetary modelBohr modified Rutherford's model of the atom by stating that electrons moved around
the nucleus in orbits of fixed sizes and energies. Electron energy in this model was quantized;
electrons could not occupy values of energy between the fixed energy levels.James Chadwick
atomic modelJames Chadwick discovered that atoms consisted not only of protons and electrons but also neutrons.
Chadwick discovered the neutron, a neutral subatomic particle that has approximately the same mass
as a proton. Neutrons occupy the nucleus of the atom.In 1926 Erwin Schrödinger, an Austrian physicist, took the Bohr atom model one step further.
Schrödinger used mathematical equations to describe the likelihood of finding an electron in
a certain position. This atomic model is known as the quantum mechanical model of the atom.
Unlike the Bohr model, the quantum mechanical model does not define the exact path of
an electron, but rather, predicts the odds of the location of the electron. This model can be
portrayed as a nucleus surrounded by an electron Erwin Schrödinger 's
quantum mechanical model
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