The atomic number of chlorine is 17. The atomic number of magnesium is 12. What is the formula for magnesium chloride? A) MgCl B) MgCl₂ C) Mg₂Cl D) MgCl₃

Question

Quizplus · Accepted Answer

In the formation of ionic compounds, the ions combine in ratios to give an overall electrically neutral compound. The cation (positive ion) is written first, followed by the anion (negative ion). The charge on the anion is obtained by subtracting the atomic number from the number of electrons in the ion. 
In this case, magnesium has a charge of +2 (since it is a metal in group 2), and chlorine has a charge of -1 (since it is a nonmetal in group 17), so the ratio of ions needed to balance the charges is 1:2. Therefore, the formula for magnesium chloride is MgCl2.

The Atomic Number of Chlorine Is 17