C1 - Nuclear Model

What did the alpha scattering experiment lead to?

The Plum Pudding Model being replaced by the Nuclear Model.

What is the main idea of the Nuclear Model?

Atoms have a tiny, dense, positively charged nucleus, with electrons orbiting around mostly empty space.

Where is most of the mass of an atom located?

In the nucleus.

Where are electrons found in the nuclear model?

Orbiting the nucleus.

Who proposed that electrons orbit the nucleus at specific distances?

Niels Bohr.

What do we now call the orbits proposed by Niels Bohr?

Energy levels or shells.

Why was Bohr's model accepted by scientists?

Because it agreed with experimental results.

What particle was discovered to cause the nucleus's positive charge?

The proton.

What does the number of protons in the nucleus determine?

The positive charge of the nucleus and the element's identity.

How many protons are in a hydrogen atom?

1

How many protons are in a helium atom?

2

Who discovered the neutron?

James Chadwick.

When was the neutron discovered?

Around 20 years after the nuclear model was proposed.

Why was the discovery of the neutron important?

It explained the missing mass in the nucleus and completed the nuclear model.

Where are neutrons located?

In the nucleus, alongside protons.

What is the radius of an atom approximately?

0.1 nanometers (1 × 10⁻¹⁰ m).

What is the radius of a nucleus approximately?

1 × 10⁻¹⁴ m.

How does the size of the nucleus compare to the atom?

The nucleus is less than 1/10,000 the size of the whole atom.

Where is nearly all of the mass of the atom found?

In the nucleus.

What does the term "relative charge" mean?

The charge of a particle compared to others.

What is the relative charge of a proton?

1

What is the relative charge of a neutron?

0 (neutral).

What is the relative charge of an electron?

-1

What does the term "relative mass" mean?

The mass of a particle compared to others.

What is the relative mass of a proton?

1

What is the relative mass of a neutron?

1

What is the relative mass of an electron?

Very small (almost zero).

Why do atoms have no overall charge?

Because they have the same number of protons (positive) and electrons (negative), which cancel out.

What does the number of electrons equal in a neutral atom?

The number of protons.

What does the neutron add to the atom?

Mass, but no charge.

Why do electrons not contribute much to the atom's mass?

Because they have a very small relative mass.

What is the modern model of the atom based on?

The nuclear model with protons and neutrons in the nucleus and electrons in energy levels.