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450 BCE
Democritus
He had the idea of a round ball of the Atom and that it could be divided infinitely -
Dalton
indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass. -
Thompson
Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup." -
Rutherford
as described by Ernest Rutherford, has a tiny, massive core called the nucleus. The nucleus has a positive charge. Electrons are particles with a negative charge. The empty space between the nucleus and the electrons takes up most of the volume of the atom. -
Bohr
dense nucleus surrounded by orbiting electrons, similar to the structure of the Solar System, but with attraction provided by electrostatic forces in place of gravity. -
Modern Quantum Cloud Model
The quantum mechanical model of the atom uses complex shapes of orbitals (sometimes called electron clouds), volumes of space in which there is likely to be an electron. So, this model is based on probability rather than certainty. ... He theorizes electrons move in waves, and they have no exact location. -
Chadwick
He believed that atoms were composed mostly of empty space, with a dense nucleus. His experiments involved shooting alpha particles at gold foil. He concluded that the positive nucleus contains most of the atom's mass.
