1. Friday October 1, 2010 (WS – ATOMIC STRUCTURE)

2. Bell Ringer Friday, 10-1-10 What do all atoms have in commom?

3. Announcements Please get your binders out!

5. John Dalton Recall that in 1808, an English schoolteacher named John Dalton reasoned that: elements were composed of atoms. only whole numbers of atoms can combine to form compounds. Expanding on these notions, Dalton published his theory on atom and their structure, characteristics, and properties.

6. The Five Key Points of Dalton’s Atomic Theory 1.All matter is composed of extremely small particles called atoms. 2.Atoms of a given element are identical in size, mass and other properties: atoms of different elements differ in these ways. 3.Atoms cannot be subdivided, created or destroyed. 4.Atoms of different elements combine in simple whole-number ratios to form compounds 5.In chemical reactions, atoms are combined, separated or rearranged.

7. Later Alterations to Dalton’s Atomic Theory Atoms are no longer thought of as indivisible. Atoms have in more recent years been divided into smaller particles: protons, neutrons and electrons. Neutrons have been further divided into quarks and gluons. We now know that are atoms of a given element do not necessarily have the same mass. Elements consist of various isotopes – same number of protons bur differing numbers of neutrons.

8. The Modern Atomic Theory Dalton turned Democritus’ idea into a scientific theory. The important concepts of all matter being composed of atoms and atoms of any one element differing from atoms of another element remain unchanged.

9. The Structure of the Atom

10. What Does an Atom Look Like?

11. We can only attempt to illustrate the structure of the atom in a simplified way.

12. What is an atom? An atom is the smallest particle of an element that retains the chemical properties of that element. An atom is the smallest particle of matter – if you break an atom into smaller pieces, those pieces are not considered to be matter. All atoms consist of two “regions” the nucleus the electron cloud

13. The Atom’s Electron Cloud The electron cloud contains electrons with a negative (-) electromagnetic charge. The electron cloud is very large compared to the nucleus. If the electron cloud of an atom was the size of this room, the nucleus would be the size of a grain of sand!

14. The Discovery of the Electron J. J. Thompson In the late 1800s, experiments were conducted in cathode-ray tubes – an electric current was passed through various gases at different temperatures. The surface of the tube opposite the cathode glowed. An object placed between the cathode and the opposite end of the tube cast a shadow on the glass. A paddle wheel placed on rails between the electrodes rolled along the rails from cathode to anode. This supported the existence of cathode rays.

15. The Discovery of the Electron Thompson hypothesized that the glow was caused by a stream of particles, and he called them cathode rays. With a current, the rays traveled through the tube from cathode to anode.

16. The Discovery of the Electron

17. The Atom’s Nucleus The nucleus of an atom is very small compared to the atom as a whole. The nucleus contains two different types of particles. protons having a positive (+) electromagnetic charge neutrons having no (0) electromagnetic charge

18. Ernest Rutherford discovered the nucleus of the atom with his famous gold foil experiment

21. The Discovery of the Nucleus The Discovery of the Atomic Nucleus

22. Worksheet Atomic Structure