Final answer:
The formula for the compound that forms between strontium (Sr) and phosphorus (P) is Sr3P2. The compound forms with this ratio to balance the charges of the ions involved: three Sr2+ ions require two P3- ions to achieve electrical neutrality.
Step-by-step explanation:
Determining the Formula for a Compound Between Sr and P
To determine the formula for the compound that forms between strontium (Sr) and phosphorus (P), we must first understand their Lewis symbols and ionic charges. Strontium is a group 2 element which means it tends to lose two electrons to form an Sr2+ ion. The Lewis symbol for strontium would be Sr with two dots representing the valence electrons being lost. On the other hand, phosphorus is a group 15 element that tends to gain three electrons to achieve a noble gas configuration, forming a P3- ion. Its Lewis symbol would be P with five dots around it, three of which are for the additional electrons it gains.
When these two ions form a compound, they do so in a ratio that balances the total positive and negative charges in the compound. Strontium donates two electrons, and phosphorus accepts three. To get a neutral compound, where the total charge is zero, we need two P3- ions for every three Sr2+ ions. Therefore, the formula of the compound is Sr3P2.