Year 7 Science · Unit 2 · Lesson 13

Atomic Number and Mass Number

Foundation Worksheet

Name

Date

Class

Learning Goals

Know that atomic number (Z) = number of protons and defines the element.
Know that mass number (A) = protons + neutrons, and neutrons = A − Z.
Find proton, neutron and electron counts for a neutral atom from Z and A.

Warm Up

Sort it!

Write each fact from the pool into the correct category box. Some facts belong to "Neither" — they are about something else entirely.

Equals the number of protons Counts protons + neutrons Is always the smaller number on a periodic table tile Tells you how heavy the atom is Is written as the symbol Z Is written as the symbol A Counts the number of electron shells Defines which element an atom is Equals Z in a neutral atom (for electrons) Gives the temperature at which an element melts

Atomic Number

Mass Number

Neither

Your Turn

Match each element tile to its particle counts

Six periodic table tiles are shown below. Write the matching letter (A–F) next to the correct proton / neutron / electron description on the right.

Tile	Symbol · Z · A	Protons / Neutrons / Electrons description
A	C · 6 · 12	11 protons, 12 neutrons, 11 electrons
B	Na · 11 · 23	8 protons, 8 neutrons, 8 electrons
C	Fe · 26 · 56	6 protons, 6 neutrons, 6 electrons
D	O · 8 · 16	13 protons, 14 neutrons, 13 electrons
E	Al · 13 · 27	26 protons, 30 neutrons, 26 electrons
F	Ca · 20 · 40	20 protons, 20 neutrons, 20 electrons

Show What You Know

1. An atom has an atomic number of 17 and a mass number of 35. How many neutrons does it have? Show your working.

Recall 2 marks

2. Why does changing the number of protons in an atom change what element it is? Use the term "atomic number" in your answer.

Recall 2 marks

Wrap Up

In one sentence, what was the main idea of this lesson?