Holding the nucleus together

The idea

Protons in a nucleus repel one another; neutrons reduce this repulsion by increasing the distance between protons and strengthen the nuclear force that binds all the particles together.

Like charges push apart

In the nucleus, many protons sit very close together. All of them carry positive charge.

What helps keep such a nucleus from flying apart?

• Neutrons
• More electrons outside
• Nothing, protons attract one another

Pushing and binding

Press Next step.

Neutrons as peacemakers

Protons push one another away. Neutrons are neutral, but they help the nucleus hold together.

Protons in a nucleus repel one another. Neutrons reduce this repulsion by increasing the distance between protons, and they strengthen the nuclear force that binds all the particles together.

Notes

Protons repel each other. Neutrons reduce the repulsion (by increasing the distance between protons) and strengthen the nuclear force that binds the nucleus.

Check yourself

Why do protons in a nucleus repel one another?

How do neutrons help the nucleus?

Why do heavier atoms need many more neutrons?

• They are much heavier than electrons. Being heavy does not cause the repulsion. It comes from the like positive charges.
• Neutrons push them away. Neutrons are neutral and reduce the repulsion between protons.
• They all carry positive charge — correct. Yes!
• They reduce the repulsion between protons and strengthen the nuclear force — correct. Yes!
• They increase the repulsion between protons. Neutrons reduce the repulsion by increasing the distance between protons.
• They give the nucleus its positive charge. The positive charge comes from the protons. Neutrons are neutral.
• To make the nucleus negatively charged. Neutrons have no charge, and the nucleus stays positive.
• To hold everything in the nucleus tightly bound — correct. Yes!
• To make the electrons move faster. The need for neutrons is about binding the nucleus together, not about the electrons.