History of the Atomic Model

Existence of Atoms - Democritus

400 BCE

Democritus was a central figure in the development of the atomic theory of the universe. Democritus suggested to the world that all objects made of matter (which is all material bodies) are made up of atoms. He stated the atoms were invisible and could not been see by the naked eye. This is true as we cannot see atoms by looking at an object. He believed atoms were uniform, solid, incompressible, and indestructible and that they moved in infinite numbers through empty space until stopped.

The Atomic Theory - John Dalton

1803

John Dalton produced the 'Atomic Theory'. The atomic theory of matter seeks to explain the nature of matter-the materials of which the Universe, all galaxies, solar systems and Earth are formed. He stated that atoms are tiny, indestructible particles. This is the same as what Democritus believed all the way back in 400 BC. Dalton also states that the different elements that we now know from the period table of elements are made up of different atoms.

Anode Rays - E. Goldstein

1896

E. Goldstein was the first to discover anode rays. This discovery helped in the later discovery of protons. An anode ray is a beam of positive ions that is created by certain types of gas-discharge tubes. They were first observed in Crookes tubes during experiments by the German scientist Eugen Goldstein, in 1886.

'Plum Pudding' - J. J. Thomson

1897

The Plum Pudding model was first developed by J. J. Thomson. He had also discovered the electron. It was put forth before the discovery of the nucleus. According to this model, the atom is a sphere of positive charge, and negatively charged electrons are embedded in it to balance the total positive charge.

Atom 'Shells' - Niels Bohr

1913

Niels Bohr used his model to state that electrons are only found in specific circular paths or orbits around the nucleus. Bohr modified his atomic structure model by explaining that electrons move in fixed orbitals (shells) and not anywhere in between and he also explained that each orbit (shell) has fixed energy levels. Rutherford basically explained the nucleus of an atom and Bohr modified that model into electrons and energy level

'Nuclear Atom' - E. Rutherford

1913

Atoms contain a dense positively charged nucleus and electrons are located around it. The 'Nuclear Atom' model described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun.

Protons - E. Rutherford

1920

Rutherford was the first person to find and define the word protons. Rutherford called the area of concentrated positive charge the nucleus. He predicted—and soon discovered—that the nucleus contains positively charged particles, which he named protons. Rutherford also predicted the existence of neutral nuclear particles called neutrons, but he failed to find them.

Electrons and Maths - E. Schrodinger

1926

E. Schrodinger ended up developing a mathematical equation related to the motion of electrons. In this equation: Ψ is the wave function, V is the potential energy, E is the energy eigenvalue, (r) denotes the quantities are functions of spherical polar coordinates (r, θ, φ)

Neutrons - J. Chadwick

1932

J. Chadwick confirmed the existence of neutrons. Nuclei contain both protons and neutrons. By 1920, physicists knew that most of the mass of the atom was located in a nucleus at its center, and that this central core contained protons. In May 1932 James Chadwick announced that the core also contained a new uncharged particle, which he called the neutron.