Year 8 Science · Unit 2 · Lesson 08
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. Isotopes of the same element have different numbers of protons.
Correct it:
2. Carbon-12 and carbon-14 are both carbon because each has 6 protons.
Correct it:
3. A carbon-14 atom has 8 neutrons.
Correct it:
4. The three isotopes of hydrogen have different atomic numbers.
Correct it:
1. In the name “carbon-14”, what does the word “carbon” tell you about the number of protons? What does the number 14 tell you?
Sort the pairs
Each chip is a pair of atoms. Write each pair in the correct box.
Isotopes of the same element
Different elements
Scenario: the glowing exit sign
Some exit signs glow in the dark with no electricity. They contain tritium, a radioactive isotope of hydrogen.
| Isotope | Protons | Mass number | Neutrons | Stable or radioactive |
|---|---|---|---|---|
| Hydrogen-1 | 1 | 1 | 0 | stable |
| Hydrogen-2 (deuterium) | 1 | 2 | 1 | stable |
| Hydrogen-3 (tritium) | 1 | 3 | radioactive | |
| Carbon-12 | 6 | 12 | 6 | stable |
| Carbon-13 | 6 | 13 | stable | |
| Carbon-14 | 6 | 14 | radioactive |
Data: standard isotope data (stable or radioactive).
2. Complete the Neutrons column of Table 1. Then explain why the tritium in the exit sign is still hydrogen, and state how it differs from hydrogen-1.
3. A student says, “Isotopes are radioactive. That is what makes them isotopes.” Use Table 1 to show whether the student is right.
4. What is an isotope? Use carbon-12 and carbon-14 to explain how two isotopes are the same and how they are different. Use the words proton number, neutron number and mass number. Finish by describing one real use of an isotope.
True or false
1. False: isotopes of the same element have the same number of protons but different numbers of neutrons. 2. True. 3. True. 4. False: all three have atomic number 1 (one proton); they differ in neutrons.
1. “Carbon” means the atom has 6 protons (atomic number 6). 14 is the mass number: protons plus neutrons in the nucleus. [2 marks]
Sort the pairs
Isotopes of the same element: ¹²₆C and ¹³₆C; ³⁵₁₇Cl and ³⁷₁₇Cl; ¹₁H and ³₁H; ¹⁶₈O and ¹⁸₈O. Different elements: ⁴⁰₁₈Ar and ⁴⁰₂₀Ca; ²³₁₁Na and ²⁴₁₂Mg; ¹⁴₆C and ¹⁴₇N.
Go Deeper
2. Neutrons: hydrogen-3, 2; carbon-13, 7; carbon-14, 8. Tritium still has 1 proton, and the proton number decides the element. It has 2 neutrons while hydrogen-1 has none, so its mass number is 3, not 1, and it is radioactive. [3 marks: 1 column; 1 same proton number; 1 difference]
3. The student is wrong. Four of the six isotopes in Table 1 are stable (hydrogen-1, hydrogen-2, carbon-12, carbon-13). An isotope is defined by having the same protons and different neutrons, not by being radioactive. [2 marks: 1 evidence, 1 correct definition]
Show What You Know
4. Marking guide (points expected): 1 isotopes are atoms of the same element with the same number of protons but different numbers of neutrons; 1 same: both have proton number (atomic number) 6, so both are carbon; 1 different: carbon-12 has 6 neutrons and carbon-14 has 8; 1 so their mass numbers differ (12 and 14), and carbon-14 is radioactive while carbon-12 is stable; 1 a correct use, for example carbon-14 dating of once-living material up to about 50 000 years old, tritium in glowing exit signs, or technetium-99m for medical scans. [5 marks]
Common error to watch for: sorting ¹⁴₆C and ¹⁴₇N as isotopes because the mass numbers match. Always compare the bottom numbers (protons) first.