When a lithium atom is made from a helium atom by adding a proton (and neutron)to the nucleus and an electron outside, the electron goes into an n = 2, ℓ=0 state rather than an n = 1, ℓ=0 state.This is an indication that electrons:
A)obey the Pauli exclusion principle
B)obey the minimum energy principle
C)undergo the Zeeman effect
D)are diffracted
E)and protons are interchangeable

Question

Quizplus · Accepted Answer

The Pauli exclusion principle states that no two electrons in an atom can have the same set of quantum numbers. In helium, the n=1, ℓ=0 state is already filled with two electrons, so the additional electron in lithium must occupy the next available state, which is n=2, ℓ=0.

When a Lithium Atom Is Made from a Helium Atom