-
450 BCE
Democritus
He would cut a piece of matter, such as an apple into small pieces.
He found that at some point the matter would be uncuttable, he called these pieces atomos. -
John Dalton
He used solid wooden balls to model atoms. He made holes in them to connect and represent compounds. He showed that a compound always consists of the same elements in the same ratio. -
John Dalton
He created a theory that had three ideas: 1) All substances are made of atoms. Atoms are the smallest particles of matter. They cannot be divided into smaller particles. They also cannot be created or destroyed. 2) All atoms of the same element are alike and have the same mass. Atoms of different elements are different and have different masses. 3) Atoms join together to form compounds. A given compound always consists of the same kinds of atoms in the same ratio. -
J.J. Thomson
He created the vacuum tube experiment which showed that an electric current consists of flowing, negatively charged particles. He also had the plum pudding model, which showed an atom as a sphere and all positive, with negative "plums" in it to equal it out.
He discovered through his experiments what are electrons and that there are subatomic particles connected to create an atom. Thomson said that negative particles couldn’t be fundamental units of matter because they are all alike. -
Ernest Rutherford
Ernest created the gold foil experiment, where he aimed a beam of alpha particles at a very thin sheet of gold foil and then a material behind that foil and when a alpha particle passed it glowed. This experiment proved Thomson wrong. -
Earnest Rutherford
Ernest Rutherford discovered the nucleus. He later discovered protons as well and that they are concentrated in an area called the nucleus. Rutherford thought that electrons randomly orbit the nucleus. He created Rutherford’s model which showed electrons moving around the nucleus in random orbits and this explain that in between the nucleus and electrons are empty space. -
Niels Bohr
He created the liquid droplet theory, a liquid drop provides an accurate representation of an atom's nucleus. This theory was instrumental in the first attempts to split uranium atoms in the 1930s, an important step in the development of the atomic bomb. He also created the quantum theory. Bohr's theory stresses the point that an experiment's results are deeply affected by the measurement tools used to carry them out. -
Niels Bohr
Bohr explained what happens inside an atom and developed a picture of atomic structure. This work earned him a Nobel Prize of his own in 1922. Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Bohr's greatest contribution to modern physics was the atomic model. The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons.
