1. The changing atom
L.O.:
Describe how the model of the atom has changed over the years.
Describe protons, neutrons and electrons in terms of relative charge and relative mass.
Describe the distribution of mass and charge within an atom.
Describe the contribution of protons and neutrons to the nucleus of an atom, in terms of atomic number and mass number.

2. Homework: Write an exam question and corresponding mark scheme
Homework: Write an exam question and corresponding mark scheme. It will be used as a starter in the next lesson.

3. Smaller then an atom… What is a subatomic particle? Name all three
Draw and label hydrogen atom
Draw and label a helium atom
Explain the properties of the subatomic particles
Extension
Draw and label a carbon atom
Draw and label an alpha particle
Draw and label a hydride ion (H+)

4. Structure of the atom
A hundred years ago people thought that the atom looked like a “plum pudding” – a sphere of positive charge with negatively charged electrons spread through it…
Ernest Rutherford, British scientist:
I did an experiment that proved this idea was wrong. I called it the “Rutherford Scattering Experiment”

5. http://phet. colorado. edu/simulations/sims. php
Ask students to come up with model (in groups)

6. Most particles passes straight through, but some bounced back towards the source.
Come up with a model of an atom that explains this result. Remember, alpha particles are positively charged.

7. The Rutherford Scattering Experiment
Alpha particles (positive charge)
Thin gold foil
Some particles passed through, some were deflected backwards
Conclusion – atom is made up of a small central nucleus surrounded by electrons orbiting in shells

8. The structure of the atom
ELECTRON – negative, mass nearly nothing
PROTON – positive, same mass as neutron (“1”)
NEUTRON – neutral, same mass as proton (“1”)

9. Task
Your task is to produce a report into one of the different models of the atom to have been developed by scientists since 1890.
Success criteria:
Information about the key scientists who developed this model of the atom.
A description of what they believed the atom looked like when they began their work.
The key experiments that they did and what they found out from them.
The conclusions that they drew from their work and the model of the atom that developed from their work.

10. Research your topic in expert groups (same numbers together, 15 min).
Rearrange groups (same letter). Brief the rest of the group on your topic (15 min)
Individual students to present to the class (15 min).
Label students: 1a, 1b, 1c, 1d. 2a, 2b, 2c, 2d
Tip: make sure you follow the success criteria.

11. Group 1 (Greek model):Anna, Keverne, Henry
Group 2 (Thomson, plum-pudding): Sharon, Mohammed, Anthony, Esther
Group 3 (Rutherford):Andreia Louise, Bilal, Christine, Christina
Group 4 (Bohr and others): Buket, Kimberly, Winifred, Omolara Tina

12. Task:
1) Describe the differences between the “plum pudding” model and the “nuclear” model.
(4 marks).
2) Use the “nuclear” model to explain the results from Rutherford’s experiment. (2 marks)
3) Why did the work of Rutherford and Marsden convince many scientists that the ‘plum
pudding’ model of the atom was incorrect? (2 marks)

13. Task:
1) “plum pudding” vs “nuclear” model.
nuclear model mass is concentrated at the
centre / nucleus. (1 mark)
plum pudding model mass is evenly distributed. (1 mark)
nuclear model positive charge occupies only a
small part of the atom. (1 mark)
plum pudding model positive charge spread throughout the atom (1 mark)

14. Task:
“plum pudding” vs “nuclear” model.
nuclear model electrons orbit some distance
from the centre / nucleus (1 mark)
plum pudding electrons embedded in the
(mass) of positive (charge) (1mark)
nuclear model the atom mainly empty space (1 mark)
plum pudding model is a‘solid’ mass (1 mark)

15. Task:
2) Use the “nuclear” model to explain the results from Rutherford’s experiment. (2 marks)
nucleus must be positive to deflect/repel alpha particles ( 1 mark)
nucleus (very) small so few alpha particles deflected backwards ( 1 mark)

16. Task:
3) Why did the work of Rutherford and Marsden convince many scientists that the ‘plum
pudding’ model of the atom was incorrect? (2 marks)