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460 BCE
Democritus
(460-370 BC)
First in naming atoms and develop a theory that matter are all made of atoms. He describes atoms as “solid, invisible, indestructible, fundamental units of matter”. -
Benjamin Franklin
(America)
(1706-1790
Developed the Law of Conservation of Charge where charge cannot be created or destroyed and opposites charges attract while same charges repel. His discovery of positive and negative charge will lead to electrons and protons in the future. -
Joseph Proust
(France 1799)
(1754-1826)
Developed the Law of Definite Proportions which is that the mass of he elements that made up an compound are in proportion. -
John Dalton
(England)
(1766-1844)
Formed the first modern Atomic Theory where all matter are created by atoms, an element is made up of the same atoms, one element's atoms are different from another elements, mixing of elements in specific ratios can create compounds, and creating shifting in the arrangement of the atoms can cause chemical reactions. -
Antoine Lavoisier
(France 1782)
(1743-1794)
Develop the theory of the Law of Conservation of Mass where mass cannot be created or destroyed. -
Eugen Goldstein
(German 1886)
(1850-1930)
Prior to J. J. Thomson's finding, he too also discovered protons but through canal rays which consists of two differently charged channels and a particle is put to remove the bonding of the particles in a gas molecule and have the particles attract to their opposite charged channels. -
Joseph John Thomson
(England 1897)
(1856-1940)
While conducting an experiment with cathode rays, he found out about protons,positively charges particles. He discovered how the cathode ray are made up of electrons, negatively charged particles which resulting in attraction of the two type of particles that makes up an atom. He also formed a theory of how a model of a atom looks like as he describe it as a plum pudding where all the electrons are in a giant proton. -
Ernest Rutherford
(New Zealand)
(1871-1937)
He tested Thomson's theory of an atom (Plum Pudding Model) using gold foils in an experiment and found out that an atom has a nucleus which is where the mass is centered and alpha particles cannot pass through. He developed a new model of an atom where it consists of the electrons orbiting around the nucleus. -
Niels Bohr
(Denmark)
(1885-1962)
He developed a new model based on Rutherford's model but it consists of a positively charges nucleus and prescribed orbitals of electrons around it. He studies the quantum theory and discovers that if the orbital of an electron gets altered, it will emit a quantum light (photon). The quantum theory is the relation between particles and the emotion of energy in an atomic or sub-atomic level. -
James Chadwick
(England)
(1891-1974)
He discovered neutrons and how he nucleus is made up of both protons and neutrons through an experiment where he allowed a large amount of alpha particles to go through the element Beryllium which resulted it to seperate the nucleus and emit he protons. This experiment help him discover the protons also have mass and develop a model of how the nucleus of an atoms is like.
