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1. Velocity of electron in nth orbit = v_{n} = 2.165 x 10^{6} Z/n m/s

2. Radius of nth orbit = r_{n} = 0.53 x 10^{–10} n^{2}/Z m

3. Binding energy of an electron in nth state = E_{n} = –13.6 Z^{2}/n^{2} eV/atom

**10. Excitation Energy**

The energy taken up by an electron to move from lower energy level to higher energy level. Generally it defined from ground state.

- Ist excitation energy = transition from n
_{1}= 1 to n_{2}= 2 - IInd excitation energy = transition from n
_{1}= 1 to n_{2}= 3 - IIIrd excitation energy = transition from n
_{1}= 1 to n_{2}= 4 and so on …. - The energy level n = 2 is also called as Ist excited state.
- The energy level n = 3 is also called as IInd excited state. & so on …

In general, excitation energy (DE) when an electron is excited from a lower state n1 to any higher state n2 is given as:

The wavelength (g) of the light emitted an also be determined by using:

**Illustration 1: A doubly ionised Lithium atom is hydrogen like with atomic number 3.**

**(i) Find the wavelength of radiation required to excite the electron in Li++ from the first to the third Bohr Orbit. (Ionization energy of the hydrogen atom equals 13.6 eV).**

**(ii) How many spectral lines are observed in the emission spectrum of the above excited system?**

**Solution:**

(ii) From the excited state (E_{3}), coming back to ground state, there can be ^{3}C_{2} = 3 possible radiations.

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