Physics 001.002.002 Nuclide Nomenclature

Alignment

Learning Intentions

By the end of the lesson, students will be able to:

• Describe a nuclide using notation.
• Identify the meaning of , and in nuclide notation.
• Determine the number of protons, neutrons and electrons in a neutral atom from notation.
• Write nuclide notation when given the element name, atomic number and mass number.

Success Criteria

By the end of the lesson, students have successfully:

• Stated that is the atomic number, which is the number of protons.
• Stated that is the mass number, which is the number of protons plus neutrons.
• Used to calculate the number of neutrons.
• Written nuclides correctly in the form .
• Distinguished between isotopes of the same element using their mass numbers.

Syllabus Reference

• Unit 1: Thermal, Nuclear and Electrical Physics
• Topic 2: Ionising Radiation and Nuclear Reactions
• Nuclear Model and Stability: Describe nuclides using nomenclature.

Phenomenon

Carbon can exist as carbon-12, carbon-13 and carbon-14. Each is carbon, so each has the same number of protons, but they have different numbers of neutrons. Carbon-14 is radioactive and is used in radiocarbon dating, while carbon-12 is stable and very common.

The question for the lesson is:

How can a short symbol such as tell us what is inside an atom’s nucleus?

Key Idea

A nuclide is a specific type of atom described by the number of protons and neutrons in its nucleus.

Nuclide notation is written as:

where:

• is the chemical symbol of the element.
• is the atomic number, equal to the number of protons.
• is the mass number, equal to the total number of protons and neutrons.

The number of neutrons is found using:

For a neutral atom:

Concept

The identity of an element is determined by its number of protons. Changing the number of protons changes the element. Changing the number of neutrons produces a different isotope of the same element.

For example:

and are both carbon because both have . They are different isotopes because they have different mass numbers.

Convention

The key conventions associated with notation are:

• The mass number is written at the upper left of the chemical symbol.
• The atomic number is written at the lower left of the chemical symbol.
• The chemical symbol identifies the element.
• The number of neutrons is not written directly, but is calculated using .
• The atomic number can be used to find the element on the periodic table.
• If the atom is neutral, the number of electrons equals the number of protons.
• If charge is included, it is written at the upper right, for example .

Misconceptions

Common misconceptions students have regarding the concept when applying it to situations and solving problems include:

• Thinking is the number of neutrons, rather than the total number of protons and neutrons.
• Thinking is the number of electrons only, rather than the number of protons.
• Thinking that changing the number of neutrons changes the element.
• Confusing mass number with atomic mass from the periodic table.
• Forgetting that the number of neutrons must be calculated using .

Further Reading

• Periodic table: atomic number and chemical symbols.
• Isotopes and radioactive dating.
• Nuclear stability and the neutron-to-proton ratio.
• Carbon-14 dating as an application of nuclide notation.

Explicit Instruction

Teacher Explanation

A nucleus contains protons and neutrons. Electrons surround the nucleus, but nuclide notation mainly describes the nucleus.

The standard form is:

where:

The mass number is:

The number of neutrons is:

For example:

This means:

• , so the element is carbon.
• , so there are 6 protons.
• , so there are 14 protons and neutrons in total.
• , so there are 8 neutrons.
• If the atom is neutral, it has 6 electrons.

Worked Examples

Worked Example 1

Describe the nuclide .

Given:

The element is carbon.

The number of protons is:

The number of neutrons is:

For a neutral atom, the number of electrons is:

Therefore, is carbon-14. It has 6 protons, 8 neutrons and 6 electrons if neutral.

Worked Example 2

Write the nuclide notation for an atom with 17 protons and 18 neutrons.

The number of protons gives the atomic number:

Element 17 is chlorine, so:

The mass number is:

Therefore, the nuclide notation is:

This is chlorine-35.

Worked Example 3

Compare and .

For :

For :

Both nuclides have , so both are carbon. They have different numbers of neutrons, so they are isotopes of carbon.

Check for Understanding

Check 1

Describe the nuclide .

Expected answer:

• Element: sodium
• Protons: 11
• Neutrons:
• Electrons if neutral: 11

Check 2

Write the nuclide notation for an atom with 8 protons and 8 neutrons.

Expected answer:

Check 3

Are and the same element? Explain.

Expected answer:

Yes. Both have , so both are chlorine. They are different isotopes because they have different mass numbers and therefore different numbers of neutrons.

Investigation (Alternative to Explicit)

Hypothesis

If students know the atomic number and mass number of a nuclide, then they can determine the number of protons, neutrons and electrons in a neutral atom.

Data Collection

Students are given isotope cards showing nuclides such as:

For each card, students record:

Nuclide	Element			Protons	Neutrons	Electrons if neutral

Analysis

Students calculate the number of neutrons using:

Students then group the cards by element and identify which cards represent isotopes of the same element.

Evaluation

Students answer:

• Which value determines the element: or ?
• Which value changes between isotopes of the same element?
• Why is still carbon even though it has more neutrons than ?
• What information is not directly shown in notation?

Problems

The following problems are designed to practise describing and writing nuclides using notation.

1. Describe by identifying the element, number of protons, neutrons and electrons if neutral.

2. Describe by identifying the element, number of protons, neutrons and electrons if neutral.

3. Write the nuclide notation for an atom with 3 protons and 4 neutrons.

4. Write the nuclide notation for an atom with 26 protons and 30 neutrons.

5. Write the nuclide notation for uranium-235, given that uranium has atomic number 92.

6. Determine the number of neutrons in .

7. Explain why and are isotopes of the same element.

8. A neutral atom has 15 protons and 16 neutrons. Identify its element, write its nuclide notation, and state the number of electrons.

9. A nuclide has notation . State , , the number of protons, the number of neutrons and the number of electrons if neutral.

10. A student says, “ and are the same because they both have mass number 14.” Explain why this is incorrect.

Followup

Self-check

Students should be able to answer these without notes:

• What does represent in notation?
• What does represent in notation?
• How do you calculate the number of neutrons?
• What makes two atoms isotopes of the same element?
• Why does the atomic number determine the element?

Next Topic

Explain why protons in the nucleus repel each other, leading into electrostatic repulsion and the need for the strong nuclear force.