Atomic models

Tomson Rutherford Bohr

Atomic models

BY Álvaro Trindade Luque

Dalton

Proposed by J. J. Thomson, discoverer of the electron in 1897, this model was prior to the discovery of protons and neutrons, so it assumed that atoms were composed of a positively charged sphere and negatively charged electrons were embedded in it, as the raisins in the pudding. This metaphor gave the model the epithet “Pruny Pudding Model.” This model made an incorrect prediction of the positive charge in the atom, since it stated that it was distributed throughout the atom. This was later corrected in Rutherford's model where the atomic nucleus was defined.

The first atomic model with scientific bases was born within chemistry, proposed by John Dalton in his “Atomic Postulates”. He maintained that everything was made of atoms, indivisible and indestructible, even through chemical reactions. Dalton proposed that the atoms of the same chemical element were equal to each other and had the same mass and the same properties.

Tomson

Ernest Rutherford conducted a series of experiments in 1911 using gold foil. In these experiments he determined that the atom is composed of a positively charged atomic nucleus (where most of its mass is concentrated) and electrons, which rotate freely around this nucleus. In this model, the existence of the atomic nucleus is proposed for the first time.

Rutherford

Bohr's model is summarized in three postulates:

• Electrons trace circular orbits around the nucleus without radiating energy.
• The orbits allowed for electrons are those with a certain value of angular momentum (L) (amount of rotation of an object) that is an integer multiple of the value, with h=6.6260664×10-34 and n=1, 2, 3….
• Electrons emit or absorb energy when jumping from one orbit to another and in doing so they emit a photon that represents the difference in energy between both orbits.

Bohr