Multiple Choice
When zinc reacts with sulfur to form an ionic compound, what is the correct formula unit of the product?
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5. Molecules and Compounds
Writing Formula Units of Ionic Compounds
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In the ionic formula , magnesium forms . Which element could X be so that the compound is electrically neutral?
A
Sodium (Na)
B
Nitrogen (N)
C
Oxygen (O)
D
Fluorine (F)
Verified step by step guidance1
Identify the charge on the magnesium ion given in the problem: magnesium forms a \(\mathrm{Mg}^{2+}\) ion, which means each magnesium ion has a charge of +2.
Look at the formula \(\mathrm{Mg}_3X_2\) and note that there are 3 magnesium ions and 2 ions of element X. The total positive charge contributed by magnesium ions is \$3 \times (+2) = +6$.
Since the compound is electrically neutral, the total negative charge from the X ions must balance the total positive charge from magnesium. Therefore, the total negative charge must be -6.
Given there are 2 X ions, each X ion must have a charge of \(\frac{-6}{2} = -3\). This means the ion formed by element X has a charge of \$3-$.
Recall common ion charges for the given elements: Sodium (Na) forms \(\mathrm{Na}^+\), Oxygen (O) forms \(\mathrm{O}^{2-}\), Fluorine (F) forms \(\mathrm{F}^-\), and Nitrogen (N) forms \(\mathrm{N}^{3-}\). Since the required charge is \$3-$, element X must be Nitrogen (N).
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