Year 8 Science · Unit 2 · Lesson 9
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Learning Goals
Order the steps
Number the events from 1 to 5 to show how sodium and chlorine form the ionic compound sodium chloride (NaCl). Event 1 = what happens first.
| Order | Event |
|---|---|
| The oppositely charged Na⁺ and Cl⁻ ions attract and join to form sodium chloride (NaCl). | |
| A sodium atom has 1 electron in its outer shell; a chlorine atom has 7. | |
| The chlorine atom gains that electron and becomes Cl⁻ (an anion). | |
| The sodium atom loses its single outer electron and becomes Na⁺ (a cation). | |
| Both ions now have a full, stable outer shell. |
Complete the table
For each atom, use its electron arrangement to work out the ion it forms. The first row is done for you.
| Atom | Electron arrangement | Electrons lost/gained | Ion formed | Cation or anion? |
|---|---|---|---|---|
| Sodium (Na) | 2, 8, 1 | loses 1 | Na⁺ | cation |
| Magnesium (Mg) | 2, 8, 2 | |||
| Chlorine (Cl) | 2, 8, 7 | |||
| Oxygen (O) | 2, 6 |
(a) Which atoms in the table formed cations, and which formed anions?
(b) What pattern do you notice: do metals (like Na and Mg) tend to lose or gain electrons? What about non-metals (like Cl and O)?
(c) Explain why an atom forms an ion at all. What does losing or gaining electrons give the atom?
1. Magnesium (Z = 12) forms an ion Mg²⁺. How many electrons does Mg²⁺ have? Did magnesium lose or gain electrons to form this ion?
2. A friend says: "A chloride ion (Cl⁻) must be a different element to chlorine because it has a different charge." Write a correction of exactly two sentences explaining why this is wrong.
Wrap Up
In one sentence, what was the main idea of this lesson?