Atomic Theory Timeline

Democritus

400 BCE

He was the first one to use the word “atom” and believe that they come in different shape, and size, and that they were also small particles and sold. Democritus proposed that matter couldn’t be divided into smaller pieces.

Dalton

1808

He created the very first atomic theory and his theory consisted on the atoms are tiny, atoms of one element are the same and different elements are different, invisible particles, and the combining elements form compounds.

Goldstein

1886

He proposed that electricity was made of electrons which are discrete negative particle and he discovered that with a perforated cathode emit a glow from the end of the tube near the cathode.

Thomson

1897

First to show that an atom was made from smaller things. He proposed the “raisin bun” atomic model and stated that the atoms are made up of positive charged material and negative charged electrons are found inside the positive charged material. Thomson discovered electrons.

Rutherford

1911

With the help of the gold foil experiment Rutherford showed that atoms have positive particles in the nucleus and are empty spaces. He discovered the nucleus and protons.

Bohr

1913

Proposed that electrons move around the nucleus in specific layers. It will emit protons when they are moving from one orbit to another with little energy. He also presented the model of the hydrogen atom.

de Broglie

1923

Discovered that electrons can act like waves with certain wavelengths, energy,and frequency and he predicted that electrons are similar in particles and waves.

Schrodinger

1926

Came up with the electron cloud model, which consisted of a dense nucleus surrounded by a cloud of electrons at various levels orbitals. With the helps of de Broglie they used mathematical equations for the behavior of the waves.

Chadwick

1932

He discovered a big part of an atom which is the neutrons, that meant that the particles had no charge. Neutrons are found in the nucleus