P4 - Alpha Scattering and The Nuclear Model

What did the ancient Greeks believe about atoms?

That atoms were tiny spheres that could not be divided

What did the discovery of the electron in 1897 prove?

That atoms have an internal structure and are not indivisible

What is the Plum Pudding Model?

A model where the atom is a ball of positive charge with electrons embedded in it

Why was the Plum Pudding Model proposed?

To explain the existence of electrons within atoms

What experiment disproved the Plum Pudding Model?

The Alpha Scattering Experiment

What was used in the Alpha Scattering Experiment?

A very thin sheet of gold foil and alpha particles

Why was gold foil used in the Alpha Scattering Experiment?

Because gold can be hammered into a very thin sheet, only a few atoms thick

What charge do alpha particles have?

Positive

What were the 3 main observations in the Alpha Scattering Experiment?

Most alpha particles passed through, some were deflected, and a few bounced back

What did scientists conclude from most alpha particles passing through the foil?

That most of the atom is empty space

What did the deflection of some alpha particles show?

That the atom has a small, positively charged center (nucleus)

What did the fact that some alpha particles bounced back show?

That the nucleus contains most of the atom's mass

What model replaced the Plum Pudding Model?

The Nuclear Model

What is the Nuclear Model of the atom?

An atom with a small, dense, positive nucleus surrounded by electrons

Who proposed that electrons orbit the nucleus at specific distances?

Niels Bohr

What are the fixed distances where electrons orbit the nucleus called?

Energy levels or shells

Why was Bohr's model accepted by scientists?

Because it matched results from other experiments

What particle did scientists later discover was responsible for the positive charge in the nucleus?

The proton

Who discovered the neutron?

James Chadwick

What is the charge of a neutron?

0 (neutral)

When was the neutron discovered?

Around 20 years after the Nuclear Model was proposed

What are the key features of the current Nuclear Model of the atom?

A small positive nucleus containing protons and neutrons, with electrons in energy levels around it