Multiple Choice
Which of the following is the correct chemical formula for copper(I) cyanide?
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3. Chemical Reactions
Naming Ionic Compounds
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Barium and iodine combine to form an ionic compound. What is the chemical formula for this compound?
A
Ba2I
B
BaI
C
Ba2I2
D
BaI2
Verified step by step guidance1
Identify the charges of the ions involved: Barium (Ba) is an alkaline earth metal in Group 2, so it forms a cation with a charge of +2, written as $\mathrm{Ba^{2+}}$.
Iodine (I) is a halogen in Group 17, so it forms an anion with a charge of -1, written as $\mathrm{I^-}$.
To form a neutral ionic compound, the total positive charge must balance the total negative charge. Since barium has a +2 charge and iodine has a -1 charge, you need two iodide ions to balance one barium ion.
Write the formula by combining one $\mathrm{Ba^{2+}}$ ion with two $\mathrm{I^-}$ ions, resulting in $\mathrm{BaI_2}$.
Confirm that the compound is electrically neutral: $+2$ from barium and $2 \times (-1) = -2$ from iodide ions sum to zero, so $\mathrm{BaI_2}$ is the correct formula.
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