If chlorine (nonmetal) has seven valence electrons while barium (metal) has
two to donate, how many chlorine atoms are needed to form an ionic bond
with barium?

Two chlorine atoms

Explanation:

Chlorine is a nonmetal belonging to group 7 of the periodic table. It has an atomic number of 17 distributed as (2, 8, 7), so it has 7 valence electrons and needs JUST ONE to complete its outermost shell.

Cl + e- ---> Cl-

On the other hand, barium is a metal belonging to group 2 on the periodic table. It has an atomic number of 56 with 2

valence electrons in its outermost shell, and gives off the two electrons to form a stable octet structure.

Ba > Ba2+ + 2e-

Thus, barium loses its 2 outermost electrons to form a Ba2+ ion, while TWO chlorine atoms receive them to form 2Cl- resulting in an ionic bond in the compound, BaCl2 (Barium Chloride)

Ba2+ + 2Cl- ---> BaCl2

yes it is balanced

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.