1. Development of the Atomic Theory READ pp. 1 - 8.

2. ATOMIC MODELS In ancient Greece Democritus argued: – Atoms were the smallest particles of matter. – “Atom”: (from Greek atomos, meaning “not able to be divided” Toga! 4 th Century B.C.

3. John Dalton’s model: Matter is made up of atoms Atoms cannot be divided into smaller pieces All atoms of an element are exactly alike Different elements are made of different atoms **An atom was a hard sphere that was the same throughout 1803

4. William Crookes’ experiment Cathode ray tube Electrode = metal that conducts electricity Anode (+) Cathode (-) Battery connected, greenish glow appeared in tube Shadow of cross fell at other end of tube Proof that something was traveling in a straight line through the tube and was deflected by the cross

5. JJ Thomson Model Discovered electrons!! Thomson thought the electrons were evenly mixed throughout the atom The CRT particles were negatively charged. These particles – electrons – are part of every kind of atom 1897

6. Ernest Rutherford Rutherford discovered that atoms contain a small, dense, positively charged center called the nucleus. 1911

7. Neils Bohr: Improvements on Rutherford’s model 1920 – protons were identified (Rutherford) 1932 - neutrons were discovered because of inconsistencies in the mass of atoms (Chadwick) Electrons + Neutrons Protons 1913  Electrons move around nucleus in different energy levels.  Valence electrons are in outermost level. They give an atom its chemical properties/reactivity

8. Niels Bohr Electrons Nucleus Electrons Bohr suggested that electrons (which have a negative charge) moved around the nucleus at certain fixed distances. Defined energy levels where electrons will likely orbit the nucleus.

9. Current Atomic Theory According to the current atomic theory, electrons are most likely to be found in the electron cloud around the nucleus. Bohr’s Model!!!!!!!!!!!!!!!

10. Matter

11. What is Matter? Matter is anything that has mass and takes up space. The basic building blocks of all matter are atoms.

12. An atom is the smallest particle into which an element can be divided and still be the same substance.

13. Parts of the Atom Proton: a positively (+) charged particle of the nucleus. Neutron: a neutral particle of the nucleus. Electron: a negatively (-) charged particle of the nucleus.

14. Electron (-) Neutron (neutral) (no charge) Proton (+) Nucleus (98% of the mass of atom) Electron Cloud (levels/orbits)

15. Atomic Mass Unit (amu): the SI unit for the masses of particles in atoms. Atomic Number: the number of protons in the nucleus of an atom. (P + ) Mass Number: number of protons and neutrons in an atom. (P + + N o ) Atomic Mass: the weighted average of the masses of all the naturally occurring isotopes of an element.

16. Molecules A particle made of two or more atoms bonded together forms a molecule. For example, two hydrogen atoms join with one oxygen atom to form a water molecule.

17. Elements An element is the simplest form of matter that cannot be changed into another simpler form by ordinary means. Examples of elements: Oxygen, Helium, Gold, Silver….

19. Compounds A substance made of two or more elements chemically combined form a compound. Example: NaCl, H 2 O, CO 2

20. What are atoms made of? Protons – Found in nucleus – Positive charge (+) Neutrons – Found in nucleus – NO charge (0) – neutral Electrons – Orbits around the nucleus – Negative charge (-) P+ N o 2e- 8e- 18e- 32 e- 8 (18) e- 8 e- 2 e-