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460 BCE
Democritus
He proposed that all matter was made up of small units named atoms. His work was not based on any real experiments or evidence. -
Dalton
John Dalton was the first to adapt Democritus’ theory into the first modern atomic model.
1.All matter consists of tiny particles called
atoms.
2.Atoms are indestructible and unchangeable.
3.Elements are characterized by the weight of their atoms.
4.When elements react, it is their atoms that have combined to form new compounds. -
Mendeleev
He created the periodic table of elements, which categorized elements according to their similarities. -
Goldstein
He discovered positive particles and the fact that particles had a charge equal and opposite to the electron. -
J.J. Thompson
He famously discovered the electron. He did this by studying the nature of the electric discharge in a high-vacuum cathode ray tube. -
Rutherford
He used the gold foil experiment to discover the modern model of the atom. He concluded that all positive charges were centralized, while negative electrons orbited the nucleus. -
Millikan
He used an oil drop experiment to determine the charge of a single electron. -
Bohr
He explained that outer orbits in an atom could hold more electrons than inner orbits. He also contributed the idea that electrons emit light by jumping orbits. -
Soddy
He came up with the concept of isotopes. He found that radiation is do to transmutation of elements. -
Heisenberg
He contributed the Uncertainty Principle, which states that no one can know the exact energy and location of an electron simultaneously. -
Chadwick
He discovered the neutron.