Barium chloride is a binary ionic compound made from the metal barium and the nonmetal chlorine. Its correct formula is obtained by combining ions so that the total charge is zero.
Key result: barium chloride has formula \(\mathrm{BaCl_2}\) and consists of \(\mathrm{Ba^{2+}}\) and \(2\) chloride ions \(\mathrm{Cl^-}\).
Step 1: Identify the ions and their charges
Barium is a Group 2 (alkaline earth) metal and typically forms a \(2+\) cation. Chlorine is a Group 17 halogen and typically forms a \(1-\) anion.
| Element | Ion formed | Typical ionic charge | Reason (periodic trend) |
|---|---|---|---|
| Barium (Ba) | \(\mathrm{Ba^{2+}}\) | \(+2\) | Group 2 metals lose 2 valence electrons |
| Chlorine (Cl) | \(\mathrm{Cl^-}\) | \(-1\) | Halogens gain 1 electron to complete an octet |
Step 2: Enforce charge neutrality to determine the formula
Ionic compounds are electrically neutral overall, so the sum of charges in one formula unit must equal zero. One \(\mathrm{Ba^{2+}}\) contributes \(+2\). Each \(\mathrm{Cl^-}\) contributes \(-1\), so two chloride ions are required:
\[ (+2) + 2 \cdot (-1) = 0 \]
Therefore, the formula is: \[ \mathrm{BaCl_2} \]
Step 3: Confirm the name from the formula
Naming a binary ionic compound uses the metal name followed by the nonmetal root with -ide:
- \(\mathrm{BaCl_2}\): barium + chloride \(\Rightarrow\) barium chloride
No Roman numeral is needed here because barium has a consistent \(+2\) charge in introductory general chemistry.
Step 4: Write the dissociation equation in water (common general chemistry use)
In aqueous solution, barium chloride behaves as a strong electrolyte and dissociates into ions:
\[ \mathrm{BaCl_2(aq) \rightarrow Ba^{2+}(aq) + 2Cl^-(aq)} \]
Frequent checks and pitfalls
- Formula must be neutral: \(\mathrm{BaCl}\) would have net charge \(+1\), so it is not a correct ionic formula unit.
- Subscripts reflect ratios, not charges: The “2” in \(\mathrm{BaCl_2}\) counts chloride ions needed for neutrality.
- Dissociation coefficients matter: \(\mathrm{BaCl_2}\) produces one \(\mathrm{Ba^{2+}}\) and two \(\mathrm{Cl^-}\), which affects concentration calculations and net ionic equations.
Optional extension: molar mass of barium chloride
Using typical periodic table atomic masses \(M(\mathrm{Ba}) \approx 137.33\ \text{g/mol}\) and \(M(\mathrm{Cl}) \approx 35.45\ \text{g/mol}\):
\[ M(\mathrm{BaCl_2}) \approx 137.33 + 2 \cdot 35.45 = 208.23\ \text{g/mol} \]