Mass number atomic number and isotopes.pptx

AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Mass number, atomic number and isotopes

Atomic structure

Lesson 2 of 10

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Warm-up

Atomic structure

Lesson 2 of 10

Answer each one, then check.

1

How many protons does carbon have?

2

What is an element?

3

What is an ion?

4

What does the atomic number tell you?

5

What is a neutron?

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Warm-up - Answers

Atomic structure

Lesson 2 of 10

1

How many protons does carbon have?

6

2

What is an element?

A substance with only one type of atom

3

What is an ion?

A charged atom

4

What does the atomic number tell you?

The number of protons

5

What is a neutron?

A neutral particle in the nucleus

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Learning Objectives

Atomic structure

Lesson 2 of 10

1

Define atomic number and mass number.

2

Work out the numbers of protons, neutrons and electrons in an atom.

3

Explain what isotopes are and relate differences in isotope symbols to identities, charges and masses.

4

Explain how atoms become positive ions.

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AQA GCSE PHYSICS · PAPER 1 · FOUNDATION & HIGHER

Atomic structure

Lesson 2 of 10

ATOMIC NUMBER AND MASS NUMBER

The atomic number is the number of protons in an atom. The mass number is the total number of protons and neutrons.

Isotopes of an element have the same number of protons but different numbers of neutrons.

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Nuclear Symbols and Isotopes

Atomic structure

Lesson 2 of 10

Same number of protons, different numbers of neutrons.

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Counting Particles

Atomic structure

Lesson 2 of 10

An atom of ¹⁴₆C is neutral. How many protons, neutrons and electrons does it have?

1

Protons

Atomic number = 6

2

Neutrons

Mass number − atomic number = 14 − 6 = 8

3

Electrons

Same as protons in a neutral atom = 6

ANSWER

6 protons, 8 neutrons and 6 electrons.

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Isotopes

Atomic structure

Lesson 2 of 10

Compare the atoms ³⁵₁₇Cl and ³⁷₁₇Cl.

1

Protons

Both have 17

2

Electrons

Both have 17 if neutral

3

Neutrons

35 − 17 = 18 and 37 − 17 = 20

ANSWER

They are isotopes: the same number of protons and electrons but different numbers of neutrons (2 more in chlorine-37).

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Ions

Atomic structure

Lesson 2 of 10

A sodium atom ²³₁₁Na loses one electron. Describe the ion formed.

1

Protons

Still 11

2

Electrons

Now 10

3

Charge

One more proton than electrons: +1

ANSWER

A positive ion, Na⁺, with 11 protons, 12 neutrons and 10 electrons.

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Key Ideas

Atomic structure

Lesson 2 of 10

Learn these.

Element

Determined by the number of protons.

Isotopes

Same element, so same chemical properties, but different masses.

Charge

Ions have an unequal number of protons and electrons.

Symbols

The mass number is the top number; the atomic number is the bottom number.

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Key Terms

Atomic structure

Lesson 2 of 10

Atomic number

The number of protons in an atom.

Mass number

The total number of protons and neutrons.

Isotopes

Atoms of the same element with different numbers of neutrons.

Ion

An atom that has lost or gained electrons.

Element

A substance made of atoms with the same number of protons.

Nuclide

A particular type of nucleus, such as carbon-14.

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Atomic structure

Lesson 2 of 10

YOUR TASK

Fill the Table

10 minutes

For ⁷₃Li and ⁶₃Li, state the number of protons, neutrons and electrons in each neutral atom. Explain why they are isotopes.

1

Use atomic number for protons.

2

Mass number minus atomic number for neutrons.

WHAT A GOOD ANSWER SHOWS

Li-7: 3 protons, 4 neutrons, 3 electrons. Li-6: 3 protons, 3 neutrons, 3 electrons. They have the same number of protons but different numbers of neutrons.

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Can I...?

Atomic structure

Lesson 2 of 10

Define atomic number.

Define mass number.

Work out neutrons.

Read a nuclear symbol.

Define isotopes.

Compare two isotopes.

Explain positive ions.

Say why isotopes react the same.

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Summary & Exam Focus

Atomic number = protons.

Mass number = protons + neutrons.

Isotopes: same protons, different neutrons.

A positive ion has lost electrons.

EXAM FOCUS

An atom has 6 protons and 8 neutrons. State its mass number. (1 mark)

Add protons and neutrons.

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