Year 7 Science · Unit 2 · Lesson 14
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Learning Goals
Order the steps
Number the events from 1 to 5 to show the correct order of how carbon-14 dating works. Event 1 = what happens first.
| Order | Event |
|---|---|
| Scientists measure the ratio of C-14 to C-12 remaining in the sample. | |
| The organism dies, and no new carbon-14 is absorbed. | |
| Scientists use the known decay rate to calculate the age of the sample. | |
| A living organism absorbs carbon-14 from the atmosphere through food or photosynthesis. | |
| The carbon-14 in the dead organism slowly decays into nitrogen-14. |
Read the graph
The bar chart below shows the relative abundance of the two most common isotopes of chlorine. Study it carefully, then answer the questions.
(a) Which isotope of chlorine is more abundant? By approximately how much?
(b) The periodic table lists chlorine's atomic mass as approximately 35.5. Why is it 35.5 and not 36, even though there are only Cl-35 and Cl-37?
(c) Both Cl-35 and Cl-37 are chlorine. Using the idea of isotopes, explain what is the same and what is different about these two atoms.
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: "C-14 must be a different element to C-12 because they have different mass numbers." 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?