Briefly explain why sulfur and phosphorus can form complicated molecules, but nonmetals in period 2 tend to form only diatomic molecules

see below

Explanation:

Sulfur and phosphorous can violate the octet rule and have an expanded octet, so molecules of these elements can contain more than eight valence electrons. In contrast, nonmetal elements in period 2 can't have an expanded octet because they don't have d orbitals. These elements must obey the octet rule and can hold only up to eight valence electrons. Period 2 elements can fill their outer orbitals by covalently bonding with one other atom of the same element.

2b2t

explanation:

2b2t

fe 55.85 g/mol and h2o 18.02 g/mol.