Year 8 Science · Unit 2 · Lesson 9
Foundation Worksheet
Learning Goals
True or false? Fix the false ones
Circle T or F. If a statement is false, correct it on the line.
1. An ion has a different number of protons from its atom.
Correct it:
2. A cation is an ion with a positive charge.
Correct it:
3. A chlorine atom that gains one electron becomes the ion Cl⁻.
Correct it:
4. Losing electrons gives an atom a negative charge.
Correct it:
5. Neon (2, 8) rarely forms ions, as its outer shell is full.
Correct it:
1. Write the symbol for a sodium ion and for a chloride ion. Which one is the cation?
Work out the charge
Subtract the electrons from the protons to get the charge. Row one is a worked example.
| Particle | Protons | Electrons | Overall charge | Cation or anion? | Symbol |
|---|---|---|---|---|---|
| Sodium | 11 | 10 | +1 | cation | Na⁺ |
| Potassium | 19 | 18 | |||
| Sulfur | 16 | 18 | |||
| Calcium | 20 | 18 |
Lose, gain or neither?
Each chip gives an atom and its electron arrangement. Write each atom in the box that shows what it usually does to reach a full outer shell.
Loses electrons (forms a cation)
Gains electrons (forms an anion)
Usually forms no ion
Scenario: the sports drink label
A sports drink “replaces electrolytes lost in sweat”. Electrolytes are dissolved ions that nerves and muscles need.
| Ion | Symbol | Amount (mg) |
|---|---|---|
| Sodium ion | Na⁺ | 290 |
| Chloride ion | Cl⁻ | 240 |
| Calcium ion | Ca²⁺ | 20 |
Source: sample label, invented for this worksheet.
2. Which ions in Table 1 are cations, and which is an anion? How many electrons did calcium lose?
3. Cl⁻ and K⁺ both have 18 electrons, so a student says they are the same. Use their protons (17 and 19) to explain why the student is wrong.
4. Explain what an ion is, and how a cation differs from an anion. Use sodium (2, 8, 1) to explain why it forms Na⁺ rather than gaining seven electrons, and why Na⁺ is still sodium.
True or false
1. False: an ion has the same number of protons as its atom; only the number of electrons changes. 2. True. 3. True. 4. False: losing negative electrons leaves more protons than electrons, so the atom becomes positive (a cation). 5. True.
1. Na⁺ and Cl⁻. Na⁺ is the cation (it is positive). [2 marks: 1 both symbols, 1 cation]
Work out the charge
Potassium: +1, cation, K⁺. Sulfur: −2, anion, S²⁻. Calcium: +2, cation, Ca²⁺.
Lose, gain or neither?
Loses electrons: magnesium, lithium, aluminium. Gains electrons: oxygen, chlorine, fluorine. Usually forms no ion: neon.
Go Deeper
2. Cations: Na⁺, Ca²⁺. Anion: Cl⁻. Calcium lost 2 electrons (charge 2+). [2 marks: 1 cations and anion, 1 calcium]
3. The number of protons decides the element: 17 protons is chlorine, 19 is potassium, so they are different elements. The chloride ion has 17 protons and 18 electrons, so its charge is −1 (anion); the potassium ion has 19 protons and 18 electrons, so its charge is +1 (cation). Having the same number of electrons does not make them the same. [2 marks: 1 protons decide the element, 1 both charges]
Show What You Know
4. Marking guide (points expected): 1 an ion is an atom that has lost or gained electrons, so it has an overall charge; 1 a cation is positive (lost electrons), an anion is negative (gained electrons); 1 sodium has 1 outer electron, and losing 1 is much easier than gaining 7; 1 losing it leaves 2, 8, a full outer shell, which is stable; 1 Na⁺ has 11 protons and 10 electrons (charge +1), and 11 protons means it is still sodium. [5 marks]
Common error to watch for: writing the charge as electrons minus protons, which gives potassium a charge of −1. Charge is protons minus electrons, so fewer electrons means positive.