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400
Democritus
Date: 400BC
Location: Greece
Democritus discovered that all matter is made up of atoms. These atoms can vary in shape, size, position and arrangement. There are infinite numbers of atoms and they cannot be destroyed.
This theory helped us to form our atomic theory today. -
Isaac Newton
Date: 1704
Location: England
Newton's theory stated that atoms are solid masses in motion, and that they are bound together with attractions or forces. He said "matter is formed of solid, massy impenetrable particles”. -
John Dalton
Date: 1803
Location: England
John Dalton created an atomic theory that said elements are made up of tiny particles called atoms. All atoms in an element are the same and have the same mass. All elements are different because they vary in weight. The atoms are not easily seperated from each other. He also discovered that a chemical reaction in the rearrangement of atoms. -
Amedeo Avogadro
Date: 1858
Location: Italy
In 1814 Amedeo created a theory about gas densities and how they worked. It wasn't until after he died in 1856 that his idea was accepted and is now known as Avogadro's Law. This law states that equal volumes of different gases, at the same temperature and pressure, contain an equal number of molecules. -
Mendeleev
Mendeleev created the Periodic Table of the elements. He arranged the 63 known elements at that time into ascending order based on their mass, and grouped them with other elements of similar properties. -
Joseph John (JJ) Thomson
Date: 1897
Location: England
JJ Thomson discovered the electron, and that atoms can be divided. He also found that atoms are made of positive cores with negatively charged particles around it. He established the "Plum Pudding" Method, which showed that electrons are surrounded by positive charges to balance them out.
His discoveries helped people to have a better understanding of the atom and what it is made up of. -
Hantaro Nagaoka
Date: 1903
Location: Japan.
Hantaro Nagaoka created an early but incorrect model of the atom. His idea was based Saturn with its rings. The nucleus was massive with electrons orbiting around it.
Although his model was incorrect, it still helped us to devolp the idea of the electrons orbiting around a nucleus in the centre. -
Lise Meitner & Otto Hahn
Date: 1907
Location: Berlin
Lise Meitner and Otto Hahn worked together studying chemistry. During this time discovered nuclear fission which is the process of splitting atoms with uranium. -
Robert Millikan
Date: 1909
Location: USA.
Robert Millikan used his oil-drop experiment to measure the charge of an electron. He also discovered that this charge was the same for every electron in 1910. -
Ernest Rutherford
Date: 1911
Location: England
He used thin gold foil and alpha particles (Positively charged) to prove that the atom is not solid. He also found that the atom has a small nucleus inside it, and negatively charged electrons circle in orbit around it.
We now know that the only sold part of an atom is the nucleus. This proves JJ Thompson’s “Plum Pudding” Model incorrect. -
Niels Bohr
Date: 1922
Location: Denmark
He did a study based on Rutherford's discovery of the nucleus. This resulted in him presenting a diagram of the atomic structure, which still represents the one we use today.
His theory said that the nucleus is in the centre of the atom, and the outer layers are each made up of a certain number of electrons.
His model helps us with the theoretical appearance of an atom and how different atoms combine. -
Hans Geiger
Date: 1928
Location: Germany
Hans Geiger co-invented the Geiger counter, a portable machine that counts and detects alpha particles. -
James Chadwick
Date: 1932
Location: England
James Chadwick did an experiment in which he used alpha particles to discovered a neutral atomic particle with a mass 0.1% more than a proton. This is known as the neutron.
In 1935 he received the Nobel Prize for his discovery. -
Enrico Fermi
Location: USA
Date: 1942
Enrico is best known for creating the first man made nuclear reactor. Power plants use nuclear reactors to create electricity. Heat from nuclear fission is passed to a working fluid (water or gas), which runs through turbines. -
Werner Heisenberg
Date: 1958
Location: Germany
Werner Heisenberg discovered the Uncertainty Principle, this stated that electrons did not travel in neat orbits.
His discovery helped clarify the modern view of the atom because scientists can compare the few numbers of atoms there are, by their movements of electrons, and how many electrons are in each atom.
