What were the weaknesses or limitations of Bohr’s model of atoms? Briefly describe the quantum mechanical model of atom.

<p><strong>&nbsp;</strong>Limitations of Bohr’s model of an atom:</p><p><strong> (i)</strong> It could not explain spectrum of multi-electron atoms.</p><p><strong> (ii)</strong> It could not explain Zeeman and Stark effects.</p><p><strong> (iii)</strong> It could not explain shape of molecules.</p><p><strong> (iv)</strong> It was not in accordance with Heisenberg’s uncertainty principle.<br>Quantum Mechanical Model: It was developed on the basis of Heisenberg’s uncertainty principle and dual behaviour of matter.</p><p>Main features of this model are given below:</p><p><strong> (i)</strong> The energy of electrons in an atom is quantized i.e. can only have certain values.</p><p><strong> (ii)</strong> The existence of quantized electronic energy levels is a direct result of the wave like properties of electrons.</p><p><strong> (iii)</strong> Both, the exact position and velocity of an electron in an atom cannot be determined simultaneously.</p><p><strong> (iv)</strong> The orbitals are filled in increasing order of energy. All the information about the electron in an atom is stored in orbital wave function Ψ.</p><p><strong> (v)</strong> From the value of Ψ^2&nbsp;at different points within atom, it is possible to predict the region around the nucleus where electron most probably will be found.</p>

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