Year 9 Science · Unit 2 · Lesson 07
Foundation Worksheet
Learning Goals
Fill the gap
Choose the correct word from the word bank. Each word is used once. Two words will not be used.
The of an atom is the number of electrons it gains or loses to reach a full outer shell. Metal atoms tend to electrons when they react. An atom that loses electrons becomes a ion, called a . Non-metal atoms tend to electrons. An atom that gains electrons has more electrons than protons, so it has a charge. This type of ion is called an .
1. Lithium has the electron configuration 2,1. Explain why lithium forms a Li⁺ ion rather than a Li⁻ ion.
2. Write the ion symbol, with its charge, for (a) a calcium atom that has lost 2 electrons and (b) a bromine atom that has gained 1 electron.
Count the electrons
An ion has the same number of protons as its atom. Only the electrons change. Complete the table. The first row is done for you.
| Particle (protons) | Electrons | Configuration |
|---|---|---|
| Sodium atom, Na (11) | 11 | 2,8,1 |
| Sodium ion, Na⁺ (11) | ||
| Chlorine atom, Cl (17) | ||
| Chloride ion, Cl⁻ (17) | ||
| Oxide ion, O²⁻ (8) |
Cross-and-swap
Swap the size of each charge to become the other ion’s subscript. Simplify if you can. Check that the charges add to zero. The first row is done for you.
3. Write the formula of each ionic compound.
| Ions | Formula | Charge check |
|---|---|---|
| Na⁺ and Cl⁻ | NaCl | (+1) + (−1) = 0 |
| K⁺ and O²⁻ | ||
| Ca²⁺ and O²⁻ | ||
| Al³⁺ and F⁻ |
Scenario: a mineral water label
A bottle of sparkling mineral water lists what is dissolved in it, but not the charges. Hydrogencarbonate (HCO₃⁻) and sulfate (SO₄²⁻) are ions made of several atoms.
| On the label | Milligrams in each litre |
|---|---|
| Calcium | 36 |
| Hydrogencarbonate | 200 |
| Magnesium | 18 |
| Chloride | 14 |
| Sodium | 11 |
| Sulfate | 9 |
Source: sample label. The values are invented but of a typical size for mineral water.
4. Write the symbol and charge for the calcium, magnesium, chloride and sodium ions. Then sort all six ions into cations and anions.
5. A student reads “calcium 36 mg/L” and says the water contains calcium metal. Calcium metal fizzes in water. Explain why the calcium in the bottle does not fizz. Use the configurations of Ca (2,8,8,2) and Ca²⁺.
6. Magnesium fluoride is used as a thin coating that stops glare on camera lenses. Explain how magnesium (2,8,2) and fluorine (2,7) atoms form ions, and why the formula is MgF₂.