Atoms and the Atomic Theory

1. Atoms and the Atomic Theory How do we know what we know?

2. Atoms • From early scientists, we have learned what atoms look like, even though we can’t see them. • Democritus named them “atomos” meaning indivisible (can’t separate) – we shortened the name to “atoms” • Through Dalton, Thomson, Rutherford, and Bohr, (and others) we have added to our understanding of what atoms look like and how they behave • At this time, if you haven’t watched the video, go to www.anastaciabrie.com and click the tab “Atomic Concepts” use headphones! • Make sure you have brief notes in your notebook about these scientists (you can add to your graphic organizer)

3. Scientists Review • Who said that atoms were solid balls? • Who said that atoms were mostly empty space? • Who added electrons? • What was the experiment that proved atoms were made of empty space? • Where did the name atoms come from? • What did Niels Bohr add to our understanding of the atom?

4. What we know: • Atoms are mostly empty space – not filled with gas, but truly empty – nothing there, NOTHING, really there is NOTHING! (thanks to Ernest Rutherford) • The nucleus is dense and solid, made of protons which are positive (P for proton, P for positive) and neutrons (N for neutrons, N for neutral) (thanks in part to John Dalton, J.J. Thomson, and Ernest Rutherford) • The electrons orbit around the nucleus in “electron clouds” and they are negative (thanks to Ernest Rutherford and Niels Bohr)

5. What it looks like: Each atom has the same structure, seen here. But the number of each proton, neutron, or electron can be different. Each different type of atom is called an “element.” There are 118 known elements in 2011. (There were only 103 when I went school. Why is that?)

6. Create this chart in your notes:

7. Completed Chart:

8. Model • Since we can’t see the atom, we used indirect evidence to figure out what it looks like • Other examples of indirect evidence • a smile means someone is happy • Results of multiple experiments are explained by creating the model of the atom ex: The Gold Foil Experiment

9. Gold Foil Experiment

10. Gold Foil Experiment

11. Summary • What does an atom look like? • How do we know?

12. Atomic Theory of Matter • In 1803, John Dalton extended his observations to include 4 rules that atoms follow • We still use his rules today! • Together, they are known as the Atomic Theory of Matter • But if we are still using these rules 200 years later, why are they a theory?

13. 1. Each element is composed of extremely small particles called atoms. • What are you wondering or questioning? • Why is this so important? Isn’t this already known?

14. 2. All atoms of a given element are identical; the atoms of different elements are different and have different properties (including mass). • What are you wondering or questioning? • What is responsible for the different properties if all atoms are made of the same things?

15. 3. Atoms of an element are not changed into different atoms by chemical reactions: atoms can neither by created nor destroyed. • What are you wondering or questioning? • What is responsible for the different properties if all atoms are made of the same stuff?

16. 4. Compounds are formed when atoms of different elements combine; a given compound always has the same number and kind of atoms. • What are you wondering or questioning? • Is this why H2O is always written the same way?

17. Some Vocabulary • Atoms form the building blocks for elements • Elements combine in fixed ratios to form compounds (each combination of atoms is called a molecule) • Compounds and elements can react and form new compounds (overall mass and number of atoms does not change!) • Mixtures are combinations of elements and compounds, can be homogeneous or heterogeneous • Substances are also compounds – where all of the molecules are the same (ex: water, salt, but not the mixture of salt and water! The molecules are different!