Write formulas for ionic compounds
Grade 10 Science Worksheet - Building Confidence
Circle the best answer, or write your answer on the line.
A sample holds 15 magnesium ions, each +2. How many chloride ions, each −1, balance them, Bo?
A sample holds 4 aluminum ions, each +3. How many oxide ions, each −2, balance them, Esme?
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Dot diagram
Ions with charges that must add to zero. A calcium atom gives one electron to each of two chlorine atoms. That makes one Ca²⁺ and two Cl⁻: +2 − 1 − 1 = 0, so the formula is CaCl₂.
On the card, how many electrons does calcium give away, Jun?
- 1
- 2
- 3
On the card, why does CaCl₂ need two chloride ions, Kira?
- Calcium has two shells
- Chlorine atoms come in pairs
- Two 1− charges balance one 2+
On the card, what is calcium's ion, Luz?
- Ca²⁻
- Ca⁺
- Ca²⁺
What charge does a sodium ion (group 1) have, Milo?
- −1
- +11
- +1
What charge does an oxide ion (group 16) have, Noah?
- −6
- +2
- −2
What charge does an aluminum ion (group 13) have, Pia?
- −3
- +13
- +3
Why is table salt's formula NaCl and not NaCl₂, Tala?
- +1 and −1 already add to zero
- Sodium needs two chlorines
- Chlorine is lighter than sodium
Do the charges in MgO add to zero, Zee?
- Yes: +2 − 2 = 0
- No: it needs two O
- No: +2 + 2 = 4