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Calcium oxide formula
The calcium oxide formula is CaO. Calcium oxide is an ionic compound, so its formula represents the simplest whole-number ratio of ions (a formula unit), not a discrete molecule.
Step-by-step: determine the ionic charges
- Calcium forms a \(2+\) ion. Calcium is in Group 2, so it commonly loses two electrons to form \( \mathrm{Ca^{2+}} \).
- Oxygen forms a \(2-\) ion (oxide). Oxygen is in Group 16, so it commonly gains two electrons to form \( \mathrm{O^{2-}} \).
Step-by-step: enforce charge neutrality
An ionic compound must be electrically neutral, meaning total positive charge equals total negative charge. Let the formula be \( Ca_xO_y \).
\[
2x = 2y \quad \Rightarrow \quad x = y
\]
The smallest whole-number solution is \(x=1\) and \(y=1\), giving \( \mathrm{CaO} \).
Quick check table (charges and ratio)
| Ion | Charge | How many needed | Total charge contributed |
|---|---|---|---|
| Calcium ion, \( \mathrm{Ca^{2+}} \) | \(+2\) | 1 | \(+2\) |
| Oxide ion, \( \mathrm{O^{2-}} \) | \(-2\) | 1 | \(-2\) |
| Net | — | — | \(0\) |
Visualization: charge balancing to obtain CaO
Optional extension: formula mass of CaO
If the calcium oxide formula is CaO, the formula mass is the sum of atomic masses:
\[ M(\mathrm{CaO}) \approx 40.08 + 16.00 = 56.08\ \text{g/mol} \]Final result
The calcium oxide formula is CaO, obtained by combining \( \mathrm{Ca^{2+}} \) and \( \mathrm{O^{2-}} \) in the smallest neutral ratio \(1:1\).
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