 # Structure Of Atom Class 11 Notes - Chapter 2

As discussed in the previous chapter, according to Dalton’s atomic theory, atoms are the building blocks of matter. In the year 1808, John Dalton proposed atomic theory saying that atom is an indivisible particle of matter. By the end of the nineteenth century, experiments proved that atoms comprise of three particles viz protons, neutrons, and electrons. Therefore, the discovery of sub-atomic particles gave rise to various atomic models to explain the structure of an atom.

## Common terminologies used – Structure Of Atom

• Electrons – These subatomic particles orbit around the nucleus. They are negatively charged particles and found in definite energy levels orbiting the nucleus.
• Protons – Theses subatomic particles are found in the nucleus. They are positively charged particles and belong to the nucleons group.
• Neutrons – Theses subatomic particles are found in the nucleus. They are neutral particles and belong to the nucleons group.
• Rutherford model – It states that during a chemical reaction, the mass of the products and reactants will always be equal.
• Bohr model – The model states that electrons orbit stable around the nucleus in certain fixed circular orbits at a distinct distance from the nucleus. These orbits are related to specific energies and are also referred to as energy levels or energy shells.
• Heisenberg uncertainty principle – The Heisenberg Uncertainty Principle states that the simultaneous determination of the velocity and position of a particle is impossible.
• Shells – A pathway followed by the electron to move around the nucleus of the atom.
• Subshells – A pathway for the electron to move within a shell.

### Few Important Questions

1. Calculate the wavenumber and frequency for the below:

Yellow light emitted from a sodium lamp has a wavelength (λ) of 580 nm

1. Calculate and provide the number of electrons for the following:
1. H+2
2. O+2
3. H2
1. Calculate the wavelength using the following details:

Mass of electron is 9.1 × 10–31 kg and K.E. is 3.0 × 10–25 J