Atomic Model

Democritus

442 BCE

Democritus’s model stated that matter consists of invisible particles called atoms and a void (empty space). He stated that atoms are indestructible and unchangeable. Also that they are homogenous, meaning they have no internal structure. His atomic model was solid, and stated all atoms differ in size, shape, mass, position and arrangement, with a void exists between them.

Billiard Ball Model (John Dalton)

1803

All elements are composed (made up) of atoms. It is impossible to divide or destroy an atom.
All atoms of the same element are alike. (One atom of oxygen is like another atom of oxygen.)
Atoms of different elements are different. (An atom of oxygen is different than an atom of hydrogen)
Atoms of different elements combine to form a compound.
Chemical reactions occur when atoms are separated, joined, or rearranged.

Plum Pudding Model (J. J Thomson)

1904

Thomson’s model was known as the "Plum Pudding Model” (or "Raisin Bread Model.") As each atom was a sphere filled with a positively charged fluid, known as the “pudding”. Scattered in this fluid were negatively charged electrons, these were the “plums” in the pudding. Thomson suggested that the positive fluid held the negatively charged electrons in the atom because of its electrical forces.

Planetary Model (Ernest Rutherford)

1911

Rutherford proposed that atoms consisted of a small dense center filled with positive charges. He named this center the nucleus. He then said that negatively charged electrons were scattered surrounding this dense, positively charged center. He stated these negatively charged electrons were held in orbit by the positively charged nucleus, due to the electrical forces.

Energy Level Model (Niels Bohr)

1913

Bohr’s atom like Rutherford’s contained a dense, positive nucleus. He expanded on Rutherford’s ideas, turning his attention to describing the electron. He stated they moved in fixed, circular orbits (or energy levels) around the nucleus, these called electron shells. These shells were at set distances from the nucleus and were the same for all atoms. He stated they became larger the further away they are from the nucleus, and that electrons furthest from the nucleus have higher energy.

Quantum Mechanical Model (Erwin Schrödinger)

1926

Schrodinger discovered that electrons don't move in orbits (or in a set path at all). He theorizes electrons move in waves, and they have no exact location.
This atomic model is known as the quantum mechanical model of the atom. Unlike the Bohr model, the quantum mechanical model does not define the exact path of an electron, but rather, predicts the odds of the location of the electron.