1. Chapter 1 Section 1
Elements and Atoms

2. Objectives
L Explain why elements are called the building blocks of all matter.
L Describe how atomic theory changed over time and understand why.
All scientific theory is always based on the best information at the time. available
Atomic theory changed as new information became available.

3. The Building Blocks Of Matter
Elements are the simplest pure substances in nature. They are made of atoms and can’t be broken down further while still having elemental properties.
Elements are often called the building blocks of all matter because all matter is made of elements or combinations of elements. Obj. L
There are 91 naturally occurring elements on Earth. The rest are man made.

4. Where Do Elements Come From?
When supermassive stars compress in on themselves due to gravity, smaller atoms of hydrogen and helium are squeezed together with such force their nuclei are “fused” together to form all of the elements in the universe.

5. Where Do Elements Come From?
These stars will then explode in the largest explosions imaginable in the universe and those elements fly out into space to seed new stars and solar systems throughout the galaxies.
APOD 9/12/14

6. Elements, Compounds and Mixtures
Elements are pure. All atoms of an element share the same properties.
Compounds are combinations of elements that are chemically bonded in a set ratio to create a new substance.
Mixtures are mixed together but not new substances.

7. Elements
Elements are made of all same atoms and have sameness about them. They can be found on the Periodic Table.

8. Compounds
When 2 or more elements chemically combine to form a new substance it is called a compound. Think of Hydrogen and Oxygen making water.
H2=O2 H2O
What happens when you mix Hydrogen and Oxygen?

9. They Explode

10. Mixtures
Mixture are just mixed together but all the parts are still what they were. Nothing has become something new and no chemical reaction has taken place.
This mix is still cereal, pretzels and chips.

11. Everything Is Made Of Atoms
Atoms are made of a small nucleus surrounded by a sea of electrons.
The nucleus contains 99% of the mass as PROTONS and NEUTRONS with the ELECTRONS swirling around it.
Electrons are so small, for now we will ignore their mass.

12. Atomic Theory
A scientific theory is just a theory. Theories change as new information becomes available and new discoveries made.
Eventually, if a theory stands the test of time it can become a postulate or even a law.
Understanding the atom came in pieces over time.
Atomic theory grew as a series of models that developed from scientific experimental evidence. As more evidence was collected, the theory and models were revised. L

13. Dalton

14. Thompson And The Electron
In 1897, J.J. Thompson discovered that atoms contain small negative charges he decided to call electrons.
He proposed that atoms must be solid chunks of positively charged material with tiny negative electrons inside.
His contribution of knowledge of the electron was a big step forward but the model would change again soon.

15. Thompson

16. Rutherford

17. The Model Would Change
In 1911, Ernest Rutherford conducted one of the most significant experiments ever done on the atom.
He fired protons at a piece of gold foil.
If atoms are solid, what would you expect the protons to do?
I would expect them to bounce off.
What did most of them do?
The passed through the foil.

18. Rutherford

19. Rutherford’s Experiment
Go to bookmarks under Rutherford’s Model Flash.

20. Rutherford What was Rutherford’s most important contribution?
He defines the nucleus of the atom and proves atoms are filled with empty space.

21. Bohr

22. Bohr Model

23. Quantum Wave Model

24. Section 1-1 Assessment 1a. What is Matter? What is an element?
Matter is anything with mass and takes up space. An element is a pure substance that can’t be broken down into other substances. (Enrich)
1b. Why are elements called the building blocks of matter?
Elements are often called the building blocks of all matter because all matter is made of elements or combinations of elements. Obj. L

25. Section 1-1 Assessment
1c. Water is a compound. Does water contain elements?
Of course it does. All compounds are made of combinations of elements in specific ratios.
What elements does water contain?
Hydrogen and Oxygen
What is the ratio?
2 hydrogen to 1 oxygen

26. Section 1-1 Assessment 2a. Why did atomic theory change over time?
Because scientists performed new experiments and obtained new understanding about atoms. The model had to be changed to accommodate this new information. This is a fundamental principal in science and is important.
2b. What information did Bohr contribute to the model of the atom?
Bohr’s model has a nucleus surrounded by electrons in orbits. This contributed to idea of energy levels.

27. Section 1-1 Assessment
2c. How is the modern model different from Bohr’s Model?
In the modern model, electrons surround the nucleus in an electron cloud and not on specific orbits.
Why did the model change?
Because scientists learned something new about atoms that electrons can be anywhere in the cloudlike region.