# 5. Lithium nitride has the chemical formula Li_3N. Rubidium is in the same chemical family as lithium. What is the formula of rubidium nitride?

We would assume $R {b}_{3} N$.
Rubidium, an alkali metal, commonly forms $R {b}^{+}$ salts, just as lithium commonly forms $L {i}^{+}$ salts. We would assume that the formula of rubidium nitride (if it exists!) is $R {b}_{3} N$.