Let’s start the introduction of the Bohr Model of the Atom.
Bohr Model of the Atom
A Danish physicist named Neil Bohr in 1913 proposed the Bohr’s atom of the model. Bohr’s atomic model is also known as Bohr Atomic Model or Bohr model. He modified the problems and drawbacks associated with Rutherford’s model of an atom. Bohr’s model of the atom can be described as follows:
- An atom is made up of three particles protons, electrons, and neutrons. Electrons have a negative charge, protons have a positive charge and neutrons have no charge. Due to the presence of an equal number of negative electrons and positive protons, the atom, on the whole, is electrically neutral.
- The electrons revolve around the nucleus in fixed circular paths is known as energy levels or shells. The energy level is counted from the centre outwards.
- Each energy level is associated with a fixed amount of energy, the shell nearest to the nucleus having minimum energy and the shell farthest from the nucleus having the maximum energy.
- The protons and neutrons are located in a small nucleus at the centre of the atom. Due to the presence of protons, the nucleus is positively charged.
- There is a limit to the number of electrons that each energy level can hold. The maximum number of electrons in energy level is 2n2, where ‘n’ is the number of energy levels. For example, the first energy level can hold a maximum of two electrons, the second energy level can hold a maximum of 8 electrons, the third energy level can hold a maximum of 18 electrons and fourth energy level can hold a maximum of 32 electrons.
- There is no change in the energy of electrons as long as they keep revolving in the same energy level, and the atom remains stable.
Rutherford’s Experiment – Discovery of Nucleus
When fast-moving alpha particles are allowed to strike a very thin gold foil in a vacuum, it is found that:
- Most of the alpha particles (α-particles) pass straight through the gold foil without any deflection from their original path; it shows that there is a lot of empty space in the atom.
- A few alpha particles are deflected through small angles and a few are deflected through large angles to show that there is a centre of positive charge in the atom which repels the positively charged alpha particles and deflects them their original path. This centre of positive charge in the atom is known as the nucleus.
- The observation that a very few alpha particles completely rebound on hitting the gold foil and turn back on their path shows that the nucleus is very dense and hard which does not allow the alpha particles to pass through it.
Characteristics of the Nucleus
- The nucleus of an atom is positively charged.
- The nucleus of an atom is very dense and hard.
- It is very small as compared to the size of the atom.
- Nucleus was discovered by Ernest Rutherford.
- The nucleus is a small positively charged part at the centre of an atom. It contains all the protons and neutrons.
- Protons and neutrons taken together are known as nucleons because they are present in the nucleus.
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Bohr’s Atomic Model Notes PDF: Click Here