Modelling atoms

1. Modelling atoms by Awhina, Justine, Lapana and Luke

2. The problem We have learnt that everything is made of atoms. Miss Mitchell told us that more than 2000 years ago a Greek called Democrite put forward the idea that atoms are so small they are invisible and cannot be divided. How can we make a model of that?

3. Moving on Democrite’s idea was forgotten while people called alchemists tried to change ordinary metals like lead into gold. In 1869 a Russian called Mendeleev made a list of the different types of atoms. These are called elements such as oxygen, iron and copper. A table is not a model!

4. At last, something we can make When Ernest Rutherford first went to England he worked with J.J Thomson. In 1897 Thomson discovered that atoms can release electrons. “That means”, said Awhina that “atoms are made up of smaller bits of matter”. “At last we can start making a model” said Luke.

5. Our first model Thomson said electrons carried a negative charge and thought of the atom as being like a plum pudding or raisin bread. The plums or the raisins were the negative electrons. “Lets make an edible model”, said Lapana and Luke. Being boys, they liked their kai. Justine insisted it should be a raisin bread model, she disliked plums, they were sour tasting.

6. Ingredients: 1 package active dry yeast 0.25 cup warm water 1 cup raisins 0.25 cup soft butter 0.25 cup sugar 1.5 teaspoons salt 0.5 cup scalded milk 3.75 cups all-purpose flour 2 eggs, beaten The result An edible model

7. A problem with our model Its gone! We were all guilty of having a slice, then another. How can you present a few crumbs as an atomic model? Luke saved the day. He suggested an A3 piece of paper and that we could put materials on it representing the electrons. “I have just the idea”, said Awhina “milk bottle tops”.

8. We glued the tops onto the paper with the heading: Thomson’s raisin bread model of the atom. Key represents the negative electron. We used just one colour. The area in the black circle represents the positive sphere. Thank you Awhina (and Fonterra)

9. Miss Mitchell, again “That is a very good start” said Miss Mitchell. “Start?” asked Lapana, speaking for the group. “Yes a start”, Miss Mitchell continued. “Remember Ernest Rutherford, he went on in 1911 to make his own model of an atom”. “More models then” said Justine. “More food then” said Luke hopefully.

10. Time out for research Ernest’s model was very different to the Greek’s model. It was mainly empty space and was divided up. At the centre was a small nucleus with a positive charge (protons) and the electrons circled it. If the size of the nucleus was a tennis ball, the edge of the atom was about 600m way.

11. Our Rutherford model Justine suggested we scale down our model and not worry about the size of the electrons and nucleus. Lapana reminded us we would need different coloured tops for the protons and the electrons. Awhina said we could use circles to show the electrons moving round the nucleus. Luke stated that the model reminded him of planets orbiting the Sun.

12. Key electron proton orbit path of electron Arā: Rutherford’s planetary model

13. Challenges from the team Awhina: how could you make a Rutherford’s model that is 3D? Justine: what materials could you use other than milk bottle tops? Lapana: later models had electrons in shells, with 2 in the first shell and up to 8 in the second shell. Make a model of carbon with 6 electrons Luke: I am interested in an edible model. What could be used for electrons and protons?

14. The last word from Miss Mitchell In Science models represent part of what is real about something. No single model can explain all the features. Models use something that is familiar to explain or describe something that is not familiar.