Atomic Structure Worksheet - GCSE - Beginner

Atomic Structure worksheet for GCSE (Key Stage 4 / GCSE (Ages 14-16)). Beginner level science practice, aligned to the UK National Curriculum. Print-ready with answer key included.

Science•Key Stage 4 / GCSE (Ages 14-16)•Atomic Structurebeginner

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Inside the Atom: Models, Isotopes and Electrons

GCSE Chemistry • Ages 14–16 • Beginner

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Instructions: Work through the activities in order. Use the key facts and worked example to guide your answers, and show calculations where needed. For written explanations, use accurate scientific vocabulary and complete sentences.

A Quick Guide to Atomic Structure

Use the facts below to answer each question. Keep answers concise, but include the key scientific terms. The worked example shows how to calculate the number of neutrons.

Key facts: The nucleus contains protons and neutrons. Electrons occupy shells around the nucleus. A proton has relative charge +1 and relative mass 1; a neutron has charge 0 and relative mass 1; an electron has charge −1 and a very small relative mass. In a neutral atom, the numbers of protons and electrons are equal.

Worked example: An atom has mass number 23 and atomic number 11. Neutrons = 23 − 11 = 12.

1. Describe where the protons, neutrons and electrons are found in an atom.

2. State the relative charge of a neutron.

3. A neutral atom has 8 protons. How many electrons does it have?

4. Calculate the number of neutrons in an atom with mass number 19 and atomic number 9.

Atomic Number and Mass Number

Use the relationship shown in the worked example. Atomic number is the number of protons; mass number is the total number of protons and neutrons. For a neutral atom, the number of electrons equals the number of protons.

Worked example: An atom has 12 protons and 13 neutrons. Its atomic number is 12 and its mass number is 12 + 13 = 25.

1. An atom has 6 protons and 6 neutrons. State its atomic number and mass number.

2. An atom has atomic number 17 and mass number 35. Calculate its number of neutrons.

3. A neutral atom has atomic number 13. State its numbers of protons and electrons.

4. An ion has 11 protons and 10 electrons. State its charge.

Isotopes: Same Element, Different Neutrons

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. Use each isotope notation to identify the atomic number and mass number, then calculate the neutron number.

1. Carbon-12 is written ¹²₆C. State its number of protons and neutrons.

2. Carbon-14 is written ¹⁴₆C. State its number of protons and neutrons.

3. Explain why carbon-12 and carbon-14 are isotopes of the same element.

4. Chlorine-37 is written ³⁷₁₇Cl. Calculate its number of neutrons.

Electron Configurations

For the first 20 elements, fill electron shells in order: the first shell holds up to 2 electrons, the second up to 8 and the third up to 8. The worked example shows the notation: 6 electrons → 2,4. Write configurations as numbers separated by commas.

Worked example: Oxygen has 8 electrons, so its electron configuration is 2,6.

1. State the electron configuration of lithium, which has 3 electrons.

2. State the electron configuration of carbon, which has 6 electrons.

3. State the electron configuration of sodium, which has 11 electrons.

4. An atom has the electron configuration 2,8,1. How many electrons does it have?

How Atomic Models Changed

The model of the atom changed as scientists gathered new evidence. Read the word bank, then choose the correct model or scientist for each statement. Each word is used once.

Word bank: Dalton's solid sphere model; Thomson's plum pudding model; Rutherford's nuclear model; Bohr's shell model; Chadwick's neutron discovery

1. Atoms were described as tiny, indivisible solid spheres.

2. Negative electrons were thought to be embedded in a sphere of positive charge.

3. Scattering results supported a tiny, dense, positively charged nucleus and mostly empty space.

4. Electrons were shown occupying fixed energy levels or shells around the nucleus.

5. The discovery of the neutron helped explain why atoms of an element can have different masses.

Explain the Evidence for a Nuclear Atom

Write one short, connected explanation. Start with what the earlier model proposed, describe the key observation from the alpha-particle scattering experiment, and explain how the observation led scientists to revise the model.

Explain how the results of Rutherford's alpha-particle scattering experiment led to a change from the plum pudding model to the nuclear model of the atom. Include what happened to most alpha particles, what happened to a small number, and what these results suggested about the atom. [6 marks]

Answer Key

Activity 1: 1. Protons and neutrons are in the nucleus; electrons occupy shells around it. ; 2. 0 ; 3. 8 ; 4. 10

Activity 2: 1. Atomic number 6; mass number 12. ; 2. 18 ; 3. 13 protons and 13 electrons. ; 4. +1

Activity 3: 1. 6 protons, 6 neutrons. ; 2. 6 protons, 8 neutrons. ; 3. Both have 6 protons, but different numbers of neutrons. ; 4. 20

Activity 4: 1. 2,1 ; 2. 2,4 ; 3. 2,8,1 ; 4. 11

Activity 5: 1. Dalton's solid sphere model ; 2. Thomson's plum pudding model ; 3. Rutherford's nuclear model ; 4. Bohr's shell model ; 5. Chadwick's neutron discovery

Activity 6: Most alpha particles passed straight through, showing that atoms are mostly empty space. A small number were deflected sharply or bounced back, showing that positive charge and most of the mass are concentrated in a tiny, dense nucleus. This evidence did not fit the plum pudding model, so it was replaced by the nuclear model.