Year 7 Science · Unit 2 · Lesson 13
Challenge Worksheet
Learning Goals
Explain it to a Year 4 student
Imagine your younger cousin (Year 4) asks: "Why does changing the number of protons in an atom change what element it is?" Use the four sentence starters below to explain this clearly. You can use everyday examples — think of it like a recipe or ID card.
"The basic idea is that every element has its own special number of protons. This number is called the…"
"A good way to think about it is like a passport or ID card. Just like your passport number is unique to you…"
"So if you add or take away even one proton from an atom, it turns into a completely different element. For example, carbon has 6 protons. If you add one more proton, it becomes…"
"One thing people often get confused about is the difference between protons and neutrons. Changing neutrons does NOT change the element because…"
1. A student argues: "The mass number is the most important number on a periodic table tile because it tells you how big the atom is." Do you agree or disagree? Explain your reasoning using the terms atomic number and mass number.
2. Scientists discovered element 118 (Oganesson, Og) only in 2002. Before it was made in a laboratory, no atoms with Z = 118 had ever existed on Earth. Using what you know about atomic number, explain why Z = 118 must be oganesson and nothing else — even before any chemical tests were done.
Wrap Up
In one sentence, what was the main idea of this lesson?