Write down the chemical formula of calcium nitrate. (Valency: Ca = 2; NO3 = 1)
The correct answer and explanation is:
The chemical formula of calcium nitrate is Ca(NO₃)₂.
Explanation:
Calcium nitrate is an ionic compound formed from calcium ions and nitrate ions. To write its correct chemical formula, you need to consider the valencies (charges) of the ions involved.
- Calcium ion (Ca²⁺): Calcium is an alkaline earth metal in Group 2 of the periodic table, and it forms a cation with a charge of +2.
- Nitrate ion (NO₃⁻): The nitrate ion is a polyatomic ion with a charge of -1.
Since calcium has a valency of 2 (Ca²⁺) and nitrate has a valency of 1 (NO₃⁻), you need two nitrate ions to balance one calcium ion to create a neutral compound.
Balancing charges:
- One Ca²⁺ ion contributes +2 charge.
- Two NO₃⁻ ions contribute 2 × (-1) = -2 charge.
The total charge in the compound is:
+2 (from Ca²⁺) + (-2) (from 2 NO₃⁻) = 0
This charge balance means the compound is electrically neutral, which is required for stable ionic compounds.
Thus, the formula combines one calcium ion with two nitrate ions, leading to the formula: Ca(NO3)2\boxed{\text{Ca(NO}_3)_2}
Additional Notes:
- The parentheses around NO₃ indicate that the nitrate ion is a polyatomic ion and that two whole nitrate ions are needed.
- Without the parentheses, writing CaNO₃₂ would be confusing because it would suggest one calcium, one nitrogen, and three oxygens, plus an extra 2 oxygens, which isn’t chemically accurate.
- Calcium nitrate is commonly used as a fertilizer because it provides both calcium and nitrogen, essential nutrients for plants.