Formal Charge and correct numbers

[katietietsworth_3c]

How do we know if an element can be negative or positive if it is impossible to make them both charged to 0?

[Andre_Galenchik_2L]

Whichever one has a higher electronegativity (a want for electrons), that element will gain the negative charge.

[jonathanjchang2E]

The positive or negative formal charge of an element is based on the surrounding electrons (bonded or lone pairs), but the formal charges of electrons in a molecule can "cancel" each other out resulting in a net charge of 0 for the molecule.