Question

how many energy levels does calcium have?
40
4
2
20

1. choose the best answer.

what is the electron configuration for calcium?
1s²2s²2p⁶3s²3p⁶4s²3d²
1s²2s²2p⁶
1s²2s²2p⁶3s²3p⁶4s²
1s²2s²2p⁶3s²3p⁶

Explanation:

• For the first question: Calcium (\(Ca\)) has an atomic number of \(20\). The number of energy levels (shells) an atom has is determined by its period number in the periodic table. Calcium is in period \(4\), so it has \(4\) energy levels.
• For the second question: The electron configuration of calcium (\(Ca\)) is \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}\). The Aufbau principle (filling electrons in order of increasing energy: \(1s<2s < 2p<3s<3p < 4s<3d\)) is followed. After filling \(3p\) (with \(6\) electrons), the next electrons go to the \(4s\) orbital (since \(4s\) has lower energy than \(3d\) for filling, although \(3d\) has lower energy for already - filled orbitals in some transition - metal ions). The configuration \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}\) accounts for all \(20\) electrons of calcium.

Answer:

• First question: \(4\)
• Second question: \(1s^{2}2s^{2}2p^{6}3s^{2}3p^{6}4s^{2}\) (the option that matches this configuration)