The Positive Core Discovery

Why it matters

Imagine firing bullets at a sheet of tissue paper, only to have some bounce straight back at you. That impossible rebound is what revealed the atom's hidden heart.

Predict first

If atoms were soft, uniform blobs of positive charge (the Plum Pudding model), what would happen to the alpha particles?

Rutherford expected them to pass through easily, like bullets through tissue paper. The few that bounced back shocked the scientific world.

• They would pass straight through with little or no deflection. — correct
• They would bounce back strongly.
• They would be absorbed completely.

What you do

Match each gold-foil observation with the shocking conclusion Rutherford drew from it.

Check yourself

Why did most alpha particles pass straight through the gold foil?

Since most particles went straight through, Rutherford concluded that the atom is not solid but mostly empty space.

What property of the nucleus caused the few alpha particles to bounce back?

The strong positive charge and high density of the tiny nucleus repelled the positive alpha particles, causing them to rebound.

In Rutherford's model, where are the electrons?

The nucleus holds the positive charge and nearly all the mass; the electrons whirl through the enormous empty space around it.

• The atom is mostly empty space. — correct
• The nucleus is negatively charged.
• The electrons blocked the path.
• It is dense and positively charged. — correct
• It is large and diffuse.
• It contains neutrons only.
• Moving through the vast empty space around the tiny nucleus — correct
• Packed inside the nucleus with the protons
• Spread evenly through a solid positive sphere