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Rutherford and Nuclear Forces

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Rutherford and Nuclear Forces

Read the briefing, then use evidence to solve the questions. Remember: the strong and weak nuclear forces act inside atomic nuclei, at extremely tiny scales.

Rutherford’s surprising evidence

Ernest Rutherford was born in New Zealand in 1871. In 1909, researchers working with him directed tiny, positively charged alpha particles at a very thin sheet of gold. Most particles passed straight through. Some changed direction, and a very small number bounced back. Rutherford reasoned that atoms must be mostly empty space, with nearly all their positive charge and mass packed into a tiny, dense centre: the nucleus. The experiment revealed the nucleus; it did not by itself explain every force inside it.

1.Rutherford’s team observed that most alpha particles passed straight through the gold foil. What does this suggest about the inside of an atom?

Atoms are mostly empty space.
Atoms are solid all the way through.
Gold atoms have no centre.
Alpha particles are uncharged.

2.A few alpha particles bounced back. What was the best explanation for this unexpected result?

3.Put the events in a sensible order by writing 1, 2 and 3 beside them: ___ Rutherford’s team fired alpha particles at gold foil. ___ The team observed how the particles scattered. ___ Rutherford proposed that atoms contain a tiny, dense nucleus.

Forces in the nucleus

Protons have positive electric charge, so they repel one another. Yet nuclei can remain together. The strong nuclear force attracts protons and neutrons to one another at very short distances and can overcome the proton–proton electrical repulsion within a nucleus. The weak nuclear force has a different role: it is involved in certain kinds of radioactive change, such as beta decay. Gravity and electromagnetic force also exist in nature, but they are not the strong and weak nuclear forces.

4.Match each force to its description.

Strong nuclear force
Weak nuclear force
Electromagnetic force

Makes two positively charged protons repel
Attracts protons and neutrons at very short distances
Is involved in some types of radioactive change

5.Complete the sentence: Protons in a nucleus electrically one another.

6.Complete the sentence: At very short distances, the nuclear force attracts protons and neutrons and helps hold the nucleus together.

7.True or false? The strong nuclear force is important inside a nucleus but acts over an extremely short range.

TrueFalse

8.Use the briefing to explain why the strong nuclear force is needed in a nucleus containing more than one proton.

9.A classmate says, “Rutherford discovered the strong nuclear force when he saw particles bounce off gold foil.” Is this fully accurate? Explain what the experiment showed and what it did not establish.

10.Sketch a simple nucleus with two protons and two neutrons. Label each particle, then add arrows or another clear symbol to show the strong nuclear attraction between neighbouring particles.

11.A radioactive nucleus changes as one type of particle changes into another. Which nuclear force is involved in certain changes of this kind?