Atomic Numbers Worksheet Collection For Teaching & Learning - Free Printable

Let's solve this worksheet step by step.

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🔍 Understanding the Concepts

- Atomic Number = number of protons in the nucleus.
- Mass Number = total number of protons + neutrons.
- Electrons = equal to protons in a neutral atom (no charge).
- Isotopes are atoms of the same element (same atomic number) with different numbers of neutrons (different mass numbers).

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✔ Step 1: Fill in the particles for each atom

#### 1. Carbon (C-12)
- Atomic number: 6 → 6 protons
- Mass number: 12 → protons + neutrons = 12
→ Neutrons = 12 - 6 = 6 neutrons
- Electrons = protons (neutral atom) → 6 electrons

> 🟦 Protons: 6
> 🟨 Neutrons: 6
> 🟩 Electrons: 6

#### 2. Carbon-13
- Atomic number: 6 → 6 protons
- Mass number: 13 → neutrons = 13 - 6 = 7 neutrons
- Electrons = 6

> 🟦 Protons: 6
> 🟨 Neutrons: 7
> 🟩 Electrons: 6

#### 3. Carbon-14
- Atomic number: 6 → 6 protons
- Mass number: 14 → neutrons = 14 - 6 = 8 neutrons
- Electrons = 6

> 🟦 Protons: 6
> 🟨 Neutrons: 8
> 🟩 Electrons: 6

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❓ What changed between the atoms?

> The number of neutrons changed.

❓ What do we call these?

> These are isotopes of carbon.

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#### 4. Oxygen
- Atomic number: 8 → 8 protons
- Mass number: 16 → neutrons = 16 - 8 = 8 neutrons
- Electrons = 8

> 🟦 Protons: 8
> 🟨 Neutrons: 8
> 🟩 Electrons: 8

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#### 5. Helium
- Atomic number: 2 → 2 protons
- Mass number: 4 → neutrons = 4 - 2 = 2 neutrons
- Electrons = 2

> 🟦 Protons: 2
> 🟨 Neutrons: 2
> 🟩 Electrons: 2

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#### 6. Sodium
- Atomic number: 11 → 11 protons
- Mass number: 23 → neutrons = 23 - 11 = 12 neutrons
- Electrons = 11

> 🟦 Protons: 11
> 🟨 Neutrons: 12
> 🟩 Electrons: 11

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✔ Final Answers:

| Atom | # Protons | # Neutrons | # Electrons |
|-------------|-----------|------------|-------------|
| Carbon | 6 | 6 | 6 |
| Carbon-13 | 6 | 7 | 6 |
| Carbon-14 | 6 | 8 | 6 |
| Oxygen | 8 | 8 | 8 |
| Helium | 2 | 2 | 2 |
| Sodium | 11 | 12 | 11 |

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🔬 Answer the Questions:

> What changed between the atoms?
> → The number of neutrons changed.

> What do we call these?
> → Isotopes

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🎨 Coloring Instructions (Example):

Choose one color for each particle:
- Proton: Red
- Neutron: Blue
- Electron: Green

Then, draw and color:
- Protons and neutrons in the central nucleus (inner circle)
- Electrons in the outer shells (concentric circles)

For example:
- In Carbon-12: Draw 6 red dots and 6 blue dots in the nucleus, and 6 green dots in the electron shells.

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✔ Final Notes:
- All isotopes of an element have the same number of protons but different numbers of neutrons.
- This explains why Carbon-12, Carbon-13, and Carbon-14 are isotopes — they’re all carbon (6 protons), but with varying neutron counts.

Let me know if you’d like a visual version or help coloring!