We’re being asked to** find the atomic number of the element** with a **completed n=2 shell**.

Recall that the ** quantum numbers** that define an electron are:

• *Principal Quantum Number* **(n)**: deals with the size and energy of the atomic orbital. The possible values for n are **1 to ∞**.

• *Angular Momentum Quantum Number ***(l)**: deals with the shape of the atomic orbital. The possible values for l are **0 to n – 1**.

• *Magnetic Quantum Number ***(m _{l})**: deals with the orientation of the atomic orbital in 3D space. The possible values for m

• *Spin Quantum Number ***(m _{s})**: deals with the spin of the electron. The possible values for m

Imagine a universe in which the value of m_{s} can be +1/2, 0, and -1/2. Assuming that all the other quantum numbers can take only the values possible in our world and that the Pauli exclusion principle applies, give the following.

the atomic number of the element with a completed n = 2 shell