Scientist Contributing to The Atomic Theory and Their Model

James Chadwick

1932 BCE

Atomic Theory:
James Chadwick played a significant role in the atomic theory, as he discovered the Neutron in atoms.Neutrons are located in the center of an atom, in the nucleus along with the protons. They have neither a positive nor negative charge, but contribute the atomic weight with the same effect as a proton.
Atomic Model Description:
The model says that we can’t know the exact location of the electron but the electrons are more likely to be in a specific area of the atom.

Louis de Broglie

1924 BCE

Atomic Theory:
He agreed with Einstein and discovered the wave nature of electrons and suggested that all matter have wave properties. Broglie is also known for his research on quantum theory
Atomic Model:
Electrons move travel like a wave and they don't go in a circular path. (Similar to the waves that are created when you play a musical instrument.)

Niels Bohr

1913 BCE

Atomic Theory:
Bohr developed the Bohr model of the atom, he proposed that energy levels of electrons are separated and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level to another.
Atomic Model Description:
This model is also known as the Bohr Model. Electrons can only occupy certain energy levels around the positive nucleus. The Bohr Model contains some errors, but it is still considered very important.

Ernest Rutherford

1909 BCE

Atomic Theory:
In 1911, he was the first to discover that atoms have a small charged nucleus surrounded by largely empty space, and are circled by tiny electrons, which became known as the Rutherford model (or planetary model) of the atom.
Atomic Model Description:
The nucleus of the atom is extremely small and positively charged, consists of the neutron and protons. The rest of the atom is mostly empty space and it contains electrons.

J.J Thompson

1897 BCE

Atomic Theory:
J.J. Thomson discovered electrons by using the cathode ray tubes and noticed that an atom can be divided. Also, he concluded atoms are made of positive cores and negatively charged particles within it.
Atomic Model Description:
A neutral atom is made up of an equal number of positive and negative particles.(the plum-pudding model)

Dimitri Mendeleev

1869 BCE

Atomic Theory:
Mendeleev is known for his work on the Periodic Law and creation of the first Periodic table. The Periodic Law states that when elements are arranged according to their atomic number, elements with similar properties will appear at regular intervals.
Atomic Model Description:
Mendeleev’s periodic table was arranged by 63 elements that were based on atomic mass and had many gaps in them because he predicted that it contain undiscovered elements with predictable properties.

John Dalton

1820 BCE

Atomic Theory:
He proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass.
Atomic Model Description:
It is often referred to as the billiard ball model. He defined an atom to be a ball like structure, the concepts of atomic nucleus and electrons were unknown at the time. If you asked Dalton to draw the diagram of an atom, he would've drawn a circle.

Democritus

370 BCE

Atomic Theory:
1. All matter consists of invisible particles called atoms.
2. Atoms are indestructible.
3. Atoms are solid but invisible.
4. Atoms are homogeneous.
5. Atoms differ in size, shape, mass, position, and arrangement.
Atomic Description:
Democritus created the first atomic model.It was simply a round sphere with no electrons, protons, or neutrons. His contribution helped people with understanding the idea of an atom.