Barium and iodine combine to form an ionic compound. What is the chemical formula for this compound?
A
BaI
B
Ba2I
C
Ba2I2
D
BaI2
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1
Identify the charges of the ions formed by barium and iodine. Barium is an alkaline earth metal in Group 2, so it forms a cation with a charge of +2, written as \(\mathrm{Ba^{2+}}\).
Iodine is a halogen in Group 17 and 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 chemical formula by combining one \(\mathrm{Ba^{2+}}\) ion with two \(\mathrm{I^-}\) ions, resulting in \(\mathrm{BaI_2}\).
Confirm that the formula is electrically neutral: \(+2\) from barium and \(2 \times (-1) = -2\) from two iodide ions sum to zero, so \(\mathrm{BaI_2}\) is the correct formula.