The electrons can be removed or gained by an atom to form an ion. They are the negatively charged subatomic particles that revolve around the nucleus of an atom and are located in an electron cloud, which is the area surrounding the nucleus of the atom. The mass of a proton is 1.676 x 10 -24 gramsand the charge is 1.602 x 10 -19 Coulombs.Įlectron was discovered by John Thomson in the year 1897. The atomic number of an atom is the number of protons present in an atom. From that, he concluded that a proton exists in a nucleus and protons are the subatomic particles that are positively charged. He projected alpha particles (called helium nuclei) at gold foil, and the positive alpha particles were deflected. Proton was first discovered by Ernest Rutherford in the year 1919 when he was performing his gold foil experiment. Protons and Neutrons together make the nucleus of an atom and are also called nucleons. The number of subatomic particles in an atom is three which includes Proton, Neutron, and Electron. However, in the early 20th century, some scientists like J.J Thomson, Rutherford, etc, showed that atoms can be further subdivided into smaller parts, and the three subatomic particles of an atom are proton, electron, and neutron. They cannot be further subdivided into smaller particles. One of his theories states that All substances are made of atoms, and they are the smallest particles of matter. He also comes with Dalton's Atomic Theory. He showed that a compound always consists of the same elements in the same ratio. He researched the properties of compounds. He did many experiments that provided evidence for atoms. In the year around 1800, a British chemist named John Dalton revived Democritus’s early ideas about the atom. He thought that a point would be reached where matter could not be cut into further small pieces. He wondered what would happen if we cut a piece of matter, such as chalk, into smaller and smaller pieces. The history of the atom begins with a Greek philosopher named Democritus around 450 B.C.
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