Question

5. a) In a mutlielectron atom, the electrons are not all in the lowest ( n =1) level. Why? b) Why is the position of Lithium in the periodic Table directly below that of Hydrogen?

Answer 1

a. When an atom is at its lowest energy, we say it is in the "ground state". But this lowest energy does not correspond to an atom with all the electrons in the n =1 (lowest) energy level. The Pauli exclusion principlestates that no two electrons can have completely identical properties. Some of the properties to consider are position, momentum, angular momentum, and energy. Electrons in the same atom are roughly at the same position, so if they have the same energy they have to have different values of some other quantity like angular momentum. But these other quantities are quantized too, so only certain combinations of properties can exist inside atoms.

Short : It violates pauli's exculsion principle.

b. Because both of them have the same no. of electrons in their valence orbit. (1). Both of them have same l,m but different n