Question

what is the name of the compound formed from na^{+1} and p^{-3}?
a sodium (i) phosphorous
b sodium phosphorous
c sodium (i) phoshide
d sodium phosphide

Explanation:

Step1: Determine the formula of the compound

To form a neutral compound, the charges must balance. The charge of $\text{Na}^{+1}$ is +1 and the charge of $\text{P}^{-3}$ is -3. Using the criss - cross method, the number of $\text{Na}^+$ ions needed is 3 (to balance the - 3 charge of $\text{P}^{3 - }$) and the number of $\text{P}^{3 - }$ ions needed is 1 (to balance the + 3 charge from 3 $\text{Na}^+$ ions). So the formula of the compound is $\text{Na}_3\text{P}$.

Step2: Name the compound

For ionic compounds formed from a metal (sodium, which is an alkali metal with a fixed oxidation state of +1) and a non - metal anion (phosphide, which is the anion formed from phosphorus, $\text{P}^{3 - }$), we use the name of the metal followed by the name of the non - metal anion. Since sodium has a fixed oxidation state, we do not need to use a Roman numeral to indicate its oxidation state. The anion formed from phosphorus is phosphide (the suffix - ide is used for monatomic anions).

Answer:

d. sodium phosphide