Question

which element would be used for shorthand electron configuration for calcium?
ar
kr
he
ne

1. choose the best answer.

how many electrons does calcium have?
20
4
40
2

Explanation:

• For the first question: In shorthand electron configuration, we use the noble gas that comes before the element in the periodic table. Calcium (Ca) has an atomic number of 20. Argon (Ar) has an atomic number of 18. The electron configuration of Ca is \([Ar]4s^{2}\). Krypton (Kr) has a higher atomic number (36) than Ca. Helium (He) and Neon (Ne) have much lower atomic numbers (2 and 10 respectively) and are too far from Ca in the periodic table for proper shorthand configuration.
• For the second question: The atomic number of an element is equal to the number of protons and, in a neutral atom, also equal to the number of electrons. Calcium has an atomic number of 20, so it has 20 electrons.

Answer:

1. \([Ar]\)
2. 20