Question

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write formula for the following binary compound which is composed of a metal and a nonmetal: sodium selenide.

(formulas with subscripts should be entered as regular text, i.e., h₂o should be entered as \h2o\).
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Explanation:

Step1: Determine the ions

Sodium (\(Na\)) is a metal. Sodium forms \(Na^+\) ion (it loses one electron as it is in group 1). Selenium (\(Se\)) is a non - metal. Selenium forms \(Se^{2 - }\) ion (it gains two electrons as it is in group 16).

Step2: Apply the criss - cross rule

To form a neutral compound, the charges must balance. For \(Na^+\) and \(Se^{2 - }\), we need 2 \(Na^+\) ions for every 1 \(Se^{2 - }\) ion.

Answer:

\(Na2Se\)