Free Printable Atomic Structure Worksheets - Free Printable

Let's solve each question on the Chemistry Atomic Structure Worksheet step by step and explain the reasoning.

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Question 1: For the atomic structure shown below right, answer the following questions.

The diagram shows:
- 11 protons (p⁺) in the nucleus
- 12 neutrons (n⁰) in the nucleus
- Electrons arranged in shells: 2 in the first shell, 8 in the second, and 1 in the third

#### i) Which element is the atom shown above?

- The number of protons determines the atomic number.
- Here, there are 11 protons, so the atomic number is 11.
- The element with atomic number 11 is Sodium.

✔ Answer: Sodium

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#### ii) What is the chemical symbol of the element?

- The chemical symbol for Sodium is Na.

✔ Answer: Na

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#### iii) What is the mass of the atom shown above?

- Mass number = number of protons + number of neutrons
- Protons = 11, Neutrons = 12 → Mass number = 11 + 12 = 23
- So, this is Sodium-23.

✔ Answer: 23

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#### iv) How many valence electrons are shown in the atom above?

- Valence electrons are the electrons in the outermost shell.
- The electron configuration is: 2, 8, 1 → Outermost shell has 1 electron.

✔ Answer: 1

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Question 2: Which subatomic particle did J.J. Thomson discover in order to create his plum pudding model of the atom?

- J.J. Thomson discovered the electron through his cathode ray tube experiments.
- He proposed the "plum pudding" model where electrons were embedded in a positively charged sphere.

✔ Answer: Electron

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Question 3: The nucleus was discovered by which scientist?

- Ernest Rutherford discovered the nucleus through his gold foil experiment in 1911.
- He found that most of the mass and positive charge was concentrated in a tiny center — the nucleus.

✔ Answer: c) Rutherford

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Question 4: What is the mass of Carbon-14?

- The number after the element name (e.g., Carbon-14) is the mass number.
- So, the mass of Carbon-14 is 14 atomic mass units (amu).

✔ Answer: 14

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Question 5: What is the number of protons in Carbon-14?

- All carbon atoms have 6 protons (atomic number of carbon is 6).
- Isotopes have the same number of protons but different neutrons.

✔ Answer: 6

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Question 6: What is the number of neutrons in Carbon-14?

- Mass number = protons + neutrons
- 14 = 6 + neutrons → neutrons = 14 – 6 = 8

✔ Answer: 8

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Question 7: What is the number of protons in the radioactive Uranium-238?

- Uranium has an atomic number of 92, meaning all uranium atoms have 92 protons.
- Uranium-238 is just one isotope of uranium.

✔ Answer: 92

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Question 8: What is the number of neutrons in Sulfur-33?

- Sulfur has atomic number 16 → 16 protons
- Mass number = 33
- Neutrons = 33 – 16 = 17

✔ Answer: 17

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Question 9: Neutral atoms of the same element can differ in

- Atoms of the same element have the same atomic number (same number of protons).
- But they can have different numbers of neutrons → these are isotopes.
- This means their mass number can differ.

So, neutral atoms of the same element can differ in:
- Mass number (due to different neutrons)
- But not atomic number or number of protons/electrons (since they're neutral and same element)

✔ Answer: a) Mass number

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Question 10: The basic principles of atomic theory were first conceived by

- John Dalton developed the modern atomic theory in the early 1800s.
- He proposed that matter is made of atoms, atoms of a given element are identical, etc.

✔ Answer: c) Dalton

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✔ Final Answers:

1.
i) Sodium
ii) Na
iii) 23
iv) 1

2. Electron
3. c) Rutherford
4. 14
5. 6
6. 8
7. 92
8. 17
9. a) Mass number
10. c) Dalton

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