An excited state is a higher energy state of an atom. It occurs when an atom acquires energy and moves from a lower to a higher energy level.
The ground state is the lowest energy state of an atom. An atom in ground state does not radiate energy. However, an atom can absorb energy and move from a lower to a higher energy level. This higher energy level is called the excited state.
The ground state configuration of sodium is 2,8,1. A configuration of 2-7-1-1 implies that an electron was promoted from the L shell to the N shell. This represents a sodium atom in excited state because energy is required to promote an electron to a higher energy level.
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