7.2 DISCOVERING ELEMENTS

Question 1

Timeline for finding electrons

Answer 1

1. 1800s, scientist took sealed tubes containing tiny amounts of gas.
2. Set up an electric circuit and applied huge voltage.
3. The gases conducted electricity.
4. Cathode rays = the rays travelled through the gas and hit the screen.
5. The glow caused by rays from negative electrode.
6. Johann Hittorf noticed a green glow on the screen.

Question 2

What did Joseph John Thomson do?

Answer 2

• Discovered the first subatomic particle.
• Developed a new model of atom

Question 3

Steps Thomson took in his investigation which led to the development of his model:

Answer 3

1. Asking scientific questions - What are cathode rays?
2. Making a hypothesis - Cathode rays move towards a positive electrode, so they might have a negative charge
3. Plan an investigation
4. Make a prediction - If I pass cathode rays between electrically charged pieces of metal, the rays will change direction. The rays will bend towards the positively charged metal.
5. Carry out the investigation
6. Make observations - Rays bend towards the positively charged metal
7. Think about the observations - Thought about the observation, supported his hypothesis
8. Make a conclusion - Cathode rays are charged. Their charge is negative./Cathode rays are made up of particles. All particles have same tiny mass, same electrical charge.

Question 4

A new model of the atom: (Joseph John Thomson)

Answer 4

An atom is a positively charged sphere with negative electrons embedded in the sphere.

Question 5

Why is Joseph John Thomson’s model of an atom named the Plum Pudding model?

Answer 5

Because it looks like a plum pudding.

Question 6

Plum Pudding model strength:

Answer 6

Has the same shape as the atom in the model.

Question 7

Plum pudding model weaknesses:

Answer 7

-Electrons are negatively charged, but the plum in the pudding have no charge.
-The sphere in the model is positively charged, but the pudding has no charge.