June 2023 NY Regents Chemistry Exam
36 Which formula represents calcium hydride? (1) CaH
(2) CaH2
(3) CaOH
(4) Ca(OH)2
Solution: Calcium hydride is an ionic compound because it is composed of a metal and a nonmetal. Calcium is a metal because it is to the left of the staircase on the Periodic Table. Hydrogen is a nonmetal (it is also on the left) but it is an exception. To write the formula, we can look at the oxidation number of each element on the Periodic Table. Calcium is +2 and hydrogen is -1. We then cross these numbers so they become subscripts of the partners.
Ca^2+ H^1-
Ca1H2 = CaH2
Answer: 2
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