Bohr’s Model of the Atom

The scientist Neils Bohr improved Rutherford’s nuclear model. Bohr proposed a model that included a positively charged nucleus in the centre with electrons orbiting the nucleus in a similar way to how planets orbit the Sun.

  • We call the orbits that are occupied by electrons energy levels or shells.

Bohr’s model is called the planetary model.

The series of energy levels are at increasing distances from the nucleus. Each energy level holds a maximum number of electrons.

  • The first energy level can hold a maximum of two electrons
  • The second energy level can hold a maximum of eight electrons
  • The third energy level can hold a maximum of eight electrons

The idea that electrons orbit the nucleus was more accepted than a general cloud of electrons. This is because it supported the results of experiments by other scientists.

Discovering the Neutron

After more experiments, Ernest Rutherford confirmed that the positive charge in the nucleus is due to small particles, which we now know as protons.

Not long after, in 1932, James Chadwick provided evidence for particles in the nucleus with no charge. These are particles we now know as neutrons.

  • James Chadwick also discovered that the neutron has the same mass as a proton

The discovery of the neutron allowed for a more improved model of the atom: