Final answer:
The formula for the compound that forms between strontium (Sr) and selenium (Se) is SrSe, where one Sr2+ cation combines with one Se2- anion to maintain charge neutrality.
Step-by-step explanation:
To predict the formula of the ionic compound that forms between strontium (Sr) and selenium (Se) using Lewis symbols, we need to consider their electron configurations and their tendencies to lose or gain electrons. Strontium is a group 2 element and will lose two electrons to form a Sr2+ cation. Selenium, being a group 16 element, will gain two electrons to form a Se2- anion
Therefore, each strontium atom can donate two electrons to two selenium atoms, satisfying the octet rule for both. However, for charge neutrality, a 1:1 ratio is needed, which means one Sr2+ cation will combine with one Se2- anion, resulting in the formation of SrSe.