New
New
Year 10
Edexcel
Higher

# Isotopes and relative atomic mass

I can write and use the standard nuclear notation for different elements and their isotopes, and calculate relative atomic mass using isotope masses and abundancies.

New
New
Year 10
Edexcel
Higher

# Isotopes and relative atomic mass

I can write and use the standard nuclear notation for different elements and their isotopes, and calculate relative atomic mass using isotope masses and abundancies.

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## Lesson details

### Key learning points

1. Atoms of many elements vary in the exact number of neutrons in their nucleus, and each version is called an isotope.
2. Existence of isotopes results in relative atomic masses of some elements not being whole numbers.
3. Standard nuclear notation shows the chemical symbol, the mass number and the atomic number of the isotope.
4. The relative atomic mass is an average value that takes account of the abundance of the isotopes of the element.

### Common misconception

Students often confuse the subatomic particle responsible for making an atom an isotope, and how isotopes are responsible for the relative atomic masses to 1 d.p.

Practice determining the number of neutrons in multiple isotopes.

### Keywords

• Isotope - An atom of an element with the same number of protons, but different mass numbers due to different numbers of neutrons.

• Proton - A subatomic particle found in the nucleus with a relative mass of 1 and a positive charge (+1).

• Neutron - A subatomic particle found in the nucleus with a relative mass of 1 and no charge.

• Mass number - Is the total number of protons and neutrons in the nucleus of an atom.

• Relative atomic mass (element) - The relative atomic mass of an element is an average value that takes account of the abundance of the isotopes of the element.

Real world examples of the use of isotopes can help students to remember what they are.
Teacher tip

### Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

## Starter quiz

### 6 Questions

Q1.
Which two subatomic particles are present in the nucleus of an atom?
electron
Q2.
The relative mass of a neutron is .
Q3.
What is the mass number of an atom?
number of protons
Correct answer: total number of protons and neutrons
number of neutrons
total number of protons and electrons
number of electrons
Q4.
Order the method for working out the number of the three subatomic particles in an atom of sodium. Start with the number of protons, then work out the number of electrons, then finally neutrons.
1 - number of protons = atomic number or proton number, for sodium = 11
2 - number of electrons = same as the number of protons, for sodium = 11
3 - mass number = total number of protons + neutrons
4 - number of neutrons = mass number - number of protons, for sodium: 23 - 11 = 12
Q5.
Match the atoms with the number of neutrons in their nucleus. Use your periodic table to help.

7

10

20

22

4

8

Q6.
Chlorine atoms mainly exist as ³⁵Cl and ³⁷Cl. Why are the mass numbers different?
They should all be the same.
³⁵Cl has 18 protons and ³⁷Cl has 20 protons.
³⁷Cl has gained two electrons to get a full outer shell.
³⁵Cl has 18 neutrons and ³⁷Cl has 20 protons.
Correct answer: ³⁵Cl has 18 neutrons and ³⁷Cl has 20 neutrons.

## Exit quiz

### 6 Questions

Q1.
Match the term to its definition.
Correct Answer:Protons,Subatomic particles with a mass of 1 and a positive charge.

Subatomic particles with a mass of 1 and a positive charge.

Correct Answer:Mass number,Total number of protons and neutrons in an atom.

Total number of protons and neutrons in an atom.

Correct Answer:Isotopes,Atoms of an element with different numbers of neutrons.

Atoms of an element with different numbers of neutrons.

Correct Answer:Neutrons,Subatomic particles with a mass of 1 and no charge.

Subatomic particles with a mass of 1 and no charge.

Q2.
Why do chlorine and copper have relative atomic masses which are not whole numbers, i.e. 35.5Cl and 63.5Cu?
They contain half a proton.
They contain half a neutron.
They have lost half an electron.
They have gained half an electron.
Correct answer: They are determined from the isotopes of the elements.
Q3.
Will the isotopes of hydrogen H-1, H-2 and H-3 have the same chemical properties? Select the correct answer to explain why or why not.
Yes, as they have the same number of protons and a different number of neutrons.
No, as they have a different number of neutrons.
Correct answer: Yes, as they have the same number of electrons.
Yes, as they have a different number of neutrons.
No, as they have the same number of protons and electrons.
Q4.
Many isotopes are radioactive and can be used for medical purposes, however their abundance is very low. Calculate the abundance of Cr-50 when Cr-52 is 84.0%, Cr-53 is 9.5% and Cr-54 is 2.5%.
Correct Answer: 4.0%, 4%, four percent, four %
Q5.
Calculate the relative atomic mass of silicon. The three silicon isotopes have atomic masses and relative abundances of 28 (92.2%), 29 amu (4.7%) and 30 amu (3.1%). Give your answer to 1d.p.