Atom Timeline worksheet - Free Printable

The image presents a matching activity titled "Discovering Parts of an Atom", where different atomic models are listed on the left and their corresponding descriptions and diagrams are on the right. The task is to match each atomic model with its correct description and diagram.

Let’s analyze and solve this step by step:

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Step 1: Understand Each Model

We have five atomic models, each proposed by a scientist in a specific year:

1. Solid sphere model (Dalton, 1803)
2. Plum pudding model (Thomson, 1897)
3. Nuclear model (Rutherford, 1911)
4. Planetary model (Bohr, 1913)
5. Quantum model (Schrödinger, 1926)

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Step 2: Match Models to Descriptions and Diagrams

Now, let's go through the descriptions and diagrams on the right side and match them correctly.

#### 1. Solid sphere model (Dalton, 1803)
- Description: "said that atoms are tiny solid spheres. Atoms of different elements are of different sizes."
- Diagram: A simple sphere (bottom-right).
- ✔ This matches the first diagram from the bottom — a plain sphere.

#### 2. Plum pudding model (Thomson, 1897)
- Description: "discovered the electron"
- Diagram: A sphere with embedded negative particles (electrons) in a positive background.
- ✔ This corresponds to the second diagram from the bottom — a sphere with small blue dots (electrons) inside a yellow positive sphere.
- Note: Thomson discovered the electron, which led to this model.

#### 3. Nuclear model (Rutherford, 1911)
- Description: "discovered the nucleus and that it had a positive charge."
- Diagram: A central red dot (+) surrounded by electrons in orbits.
- ✔ This matches the third diagram — a central nucleus with electrons orbiting around it.
- Rutherford’s gold foil experiment led to the discovery of the nucleus.

#### 4. Planetary model (Bohr, 1913)
- Description: "discovered that electrons move around the nucleus in specific orbits."
- Diagram: Electrons in fixed circular orbits around the nucleus.
- ✔ This matches the fourth diagram — clearly shows electrons in distinct orbits.
- Bohr improved Rutherford’s model by introducing quantized energy levels.

#### 5. Quantum model (Schrödinger, 1926)
- Description: "Electrons form an electron cloud"
- Diagram: A nucleus with a fuzzy cloud around it, showing probability regions.
- ✔ This matches the topmost diagram — a nucleus with a diffuse cloud indicating electron probability.

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Final Matching Summary

| Atomic Model | Scientist & Year | Description | Diagram |
|--------------|------------------|-------------|---------|
| Solid sphere model | Dalton, 1803 | Said atoms are tiny solid spheres. Atoms of different elements are of different sizes. | Bottom diagram (plain sphere) |
| Plum pudding model | Thomson, 1897 | Discovered the electron | Second from bottom (electrons in positive sphere) |
| Nuclear model | Rutherford, 1911 | Discovered the nucleus and that it had a positive charge | Third from bottom (central nucleus + orbiting electrons) |
| Planetary model | Bohr, 1913 | Discovered that electrons move around the nucleus in specific orbits | Fourth from bottom (fixed orbits) |
| Quantum model | Schrödinger, 1926 | Electrons form an electron cloud | Top diagram (electron cloud) |

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Answer Key (Matching):

1. Solid sphere model (Dalton, 1803) → *"said that atoms are tiny solid spheres..."* → Bottom diagram
2. Plum pudding model (Thomson, 1897) → *"discovered the electron"* → Second from bottom
3. Nuclear model (Rutherford, 1911) → *"discovered the nucleus and that it had a positive charge"* → Third from bottom
4. Planetary model (Bohr, 1913) → *"discovered that electrons move around the nucleus in specific orbits"* → Fourth from bottom
5. Quantum model (Schrödinger, 1926) → *"Electrons form an electron cloud"* → Top diagram

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✔ Conclusion:

The task involves matching historical atomic models to their correct descriptions and visual representations. By understanding the contributions of each scientist, we can correctly pair them as shown above.

This progression illustrates how our understanding of the atom evolved over time—from a simple solid sphere to a complex quantum model based on probability.