AFOQT Practice Test

How many electrons can be held in the first shell of an atom?

1. 4

2. 2

3. 8

4. 10

The correct answer is: 2

The first shell of an atom can hold a maximum of two electrons. This is consistent with the principles of quantum mechanics and atomic structure, specifically the Pauli Exclusion Principle, which states that no two electrons can occupy the same quantum state simultaneously. The first shell corresponds to the principal quantum number n=1, and according to the formula 2n², when n=1, the maximum number of electrons is 2(1)² = 2. For an atom to be stable, it typically wants to have its electrons fill the lowest energy levels first, starting from the first shell. Higher energy levels, or shells, can accommodate more electrons, which is why the second shell can hold 8 electrons and the third shell can hold up to 18 electrons, but for the first shell, the limit is firmly set at 2. This fundamental concept is crucial in understanding chemical bonding and the behavior of elements in the periodic table.