Question

iron (fe) and chlorine (cl) have the following charges.

• fe charge = 3+
• cl charge = 1-

which of the following predicts the formula for an iron chloride compound based on the balance of charges?
ⓐ the formula should be fecl₃.
fe: 1 atom because 3+ ×1 = +3
cl: 3 atoms because 1- ×3 = -3
+3 + -3 = 0
ⓑ the formula should be fe₃cl.
fe: 3 atoms because 1- ×3 = -3
cl: 1 atom because 3+ ×1 = +3
+3 + -3 = 0
ⓒ the formula should be fe₃cl.
fe: 3 atoms because the charge is 3+
cl: 1 atom because the charge is 1-
ⓓ the formula should be fecl.
fe: 1 atom because 3+ ×1 = +3
cl: 1 atom because 1- ×1 = -1

Explanation:

Step1: Recall charge balance rule

In an ionic compound, the total positive charge equals the total negative charge (net charge = 0). For Fe (charge \(3+\)) and Cl (charge \(1-\)), let the number of Fe atoms be \(x\) and Cl atoms be \(y\). Then \(3x + (-1)y = 0\), so \(3x = y\).

Step2: Analyze Option A

• Fe: 1 atom, charge contribution: \(3+\times1 = +3\)
• Cl: 3 atoms, charge contribution: \(1-\times3 = -3\)
• Total charge: \(+3 + (-3) = 0\), satisfies charge balance. Formula is \(FeCl_3\).

Step3: Analyze Option B

• Fe: 3 atoms, charge: \(1-\times3=-3\) (incorrect, Fe charge is \(3+\), not \(1-\))
• Cl: 1 atom, charge: \(3+\times1 = +3\) (incorrect, Cl charge is \(1-\), not \(3+\))
• Total charge calculation wrong, formula \(Fe_3Cl\) invalid.

Step4: Analyze Option C

• Fe: 3 atoms (reasoning wrong, charge balance not used)
• Cl: 1 atom (reasoning wrong, charge balance not used)
• Total charge: \(3\times3+(-1)\times1 = 9 - 1 = 8

eq0\), invalid.

Step5: Analyze Option D

• Fe: 1 atom, charge: \(+3\)
• Cl: 1 atom, charge: \(-1\)
• Total charge: \(+3 + (-1) = +2

eq0\), invalid.

Answer:

A. The formula should be \(FeCl_3\).
Fe: 1 atom because \(3+\times1 = +3\)
Cl: 3 atoms because \(1-\times3 = -3\)
\(+3 + -3 = 0\)