Atomic Number and Mass Number Worksheet

Question 1

An atom contains 8 protons and 10 neutrons. Which pair describes its nucleus?

1. Z = 10, A = 18
2. Z = 8, A = 18
3. Z = 8, A = 10
4. Z = 18, A = 8

Question 2

A phosphorus atom has a mass number of 31. Use the periodic table to determine its number of neutrons. Show your calculation.

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Question 3

Which two nuclei are isotopes of the same element?

1. 7 protons and 7 neutrons; 8 protons and 7 neutrons
2. 6 protons and 8 neutrons; 7 protons and 7 neutrons
3. 7 protons and 7 neutrons; 7 protons and 8 neutrons
4. 6 protons and 7 neutrons; 8 protons and 7 neutrons

Question 4

The periodic table lists 35.45 for chlorine’s atomic mass. Explain why 35.45 cannot be the mass number of a single chlorine atom.

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Question 5

What is the mass number of nucleus S?

1. 8
2. 10
3. 16
4. 18

Question 6

Identify the elements represented by S and T. Use proton counts to justify both identifications.

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Question 7

A student claims that R and S are different elements because their masses differ. Explain how the model shows that they are isotopes of one element.

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Question 8

If atom T is neutral, how many electrons does it have?

1. 0
2. 1
3. 2
4. 3