Chapter 3

Nucleus of an atom has 6 protons and 8 neutrons. Calculate at. no., mass no. and no. of electrons in neutral atom. What is the symbol of atom?

Uranium has at. no. 92 and atomic weight \(238.029 .\) Calculate the number of protons, neutrons and electrons in uranium atom.

Find energy of each of the photons which : (a) correspond to light of frequency \(3 \times 10^{15} \mathrm{~Hz}\) (b) have wavelength of \(0.50 \mathrm{~A}\).

The Vividh Bharati Station of All India Radio, Delhi broadcasts on a frequency of \(1368 \mathrm{kHz}\) (kilo hertz). Calculate the wavelength and wave number of the electromagnetic radiation emitted by the transmitter. Which part of the electromagnetic spectrum does it belong to?

$$ \begin{aligned} &\text { Calculate the mass of a photon of sodium light having wavelength }\\\ &5894 \AA \text { and velocity, } 3 \times 10^{8} \mathrm{~ms}^{-1}, h=6.6 \times 10^{-34} \mathrm{~kg} \mathrm{~m}^{2} \mathrm{~s}^{-1} \end{aligned} $$

What is the wavelength of light emitted when the electron in a hydrogen atom undergoes transition from an energy level with \(n=4\) to an energy level with \(n=2 ?\)

How much energy is required to ionise a H-atom if the electron occupies \(n=5\) orbit? Compare your answer with the ionization energy of \(\mathrm{H}\) -atom (energy required to remove the electron from \(n=1\) orbit).

Calculate the radius of Bohr's fifth orbit for hydrogen atom.

Calculate the wave number for the longest wavelength transition in the Balmer series of atomic hydrogen. \(\left(R_{11}=109677 \mathrm{~cm}^{-1}\right)\)

The electron energy in hydrogen atom is given by \(E n=\) \(\left(-2.18 \times 10^{-18}\right) / n^{2} \mathrm{~J}\). Calculate the energy required to remove an electron completely from the \(n=2\) orbit. What is the longest wavelength of light in \(\mathrm{cm}\) that can be used to cause this transition?