Development of the Atomic Model

Lab Brief #8

🎯 Your mission

Master the concept. Use it tomorrow.

⚡ The twist

Mixing two safe things doesn't always make a safe thing.

What you'll learn

Dalton's indivisible sphere gave way to Thomson's plum pudding, then Rutherford's gold-foil experiment revealed a tiny dense nucleus. Bohr added fixed energy shells, and the modern model treats electrons as probability clouds. Each change was forced by new evidence.

Key words

plum pudding model
Thomson's model of a positive sphere with embedded electrons.
gold-foil experiment
Rutherford's test whose deflected alpha particles revealed the nucleus.

Make a hypothesis first

Predict: will the mixture get hotter, colder, or stay the same?

Say your guess out loud — then find out if you were right.

Step 1 of 4 · Read

Think about what you just learned: say what "plum pudding model" and "gold-foil experiment" mean in your own words before you start.

Step 2 of 4 · Do

Build a timeline of five atomic models. For each, state the experimental evidence that made the previous model untenable, and identify what each new model could explain that the old one could not.

Step 3 of 4 · Observe

Record what actually happened, including anything that did not match what you expected.

Step 4 of 4 · Record

Write a conclusion that answers the question this lesson opened with, and state your uncertainty.

Question 1 of 2

Rutherford's gold-foil result showed the atom has a:

How sure are you?😐 maybe

Question 2 of 2

Scientific models are replaced when:

How sure are you?😐 maybe

Mind = blown

💧 Hot water can freeze faster than cold water under the right conditions. Nobody fully understands why.

Nice work!

You got 0 of 2 right.

All lessons

🎯

Next Smart Experiment

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✨ More to explore

🌍 Where you see this in real life: This is happening in your kitchen right now — every time food cooks.

🏆 Stretch challenge (try it this week): Find one ingredient in a snack and look up what it does.

👨‍👩‍👧 For the dinner table: “What's something we cook that mixes things together this way?”

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