Year 8 Science · Unit 2 · Lesson 07
Challenge Worksheet
Learning Goals
Explain it to a friend who missed this lesson
Your friend was away for Lesson 07 and wants to understand atomic number and mass number before the test. Use the sentence starters below to write a clear, accurate explanation. You can use the worked examples from class (¹H, ¹²C, ²³Na, ⁵⁶Fe) to help.
"The atomic number tells you…"
"The mass number is different because it also includes…"
"To find the number of neutrons you use the formula…"
"The reason atomic number is more important for identifying an element is…"
1. Consider a carbon atom (Z = 6, A = 12). Predict what would happen to the identity of the atom if: (i) you added one proton to its nucleus, and (ii) you added one neutron to its nucleus instead. Then explain what this tells us about which number, atomic number or mass number, is more fundamental for defining an element.
2. At ANSTO (Australian Nuclear Science and Technology Organisation), scientists work with technetium-99m, which has Z = 43 and A = 99. A journalist writes: "This isotope has an atomic mass of 99, which means it has 99 protons." Identify the error in this statement and explain, using the correct definitions of atomic number and mass number, what the values Z = 43 and A = 99 actually tell us about technetium-99m.
Wrap Up
In one sentence, what was the main idea of this lesson?