How does an atom of chlorine-37 become a chloride ion with a - 1 charge?

17

35.45

O

A. The atom gains 1 electron, to make a total of 21.

O

B. The atom gains 1 electron, to make a total of 18.

O

C. The atom loses 1 proton, to make a total of 36.

O

D. The atom loses 1 proton, to make a total of 16.

B. The atom gains 1 electron, to make a total of 18 electrons.

Explanation:

Chlorine is the 17th element in the periodic table, so it has atomic number 17:

Z = 17

This means that a neutral atom of chlorine has 17 protons and 17 electrons.

When a chlorine atom gains 1 electron, its electric charge (initially zero) becomes - 1, since the electron has negative charge of - 1 (in elemntary charge units). This also means that the number of electrons in the ion is now

17 + 1 = 18

So the correct answer is

B. The atom gains 1 electron, to make a total of 18 electrons