1. ATOMS - Matter is made up of elements and elements in turn are made up of atoms. - Macroscopic world v. Microscopic world - The unraveling of the structure of the atom is like working on a jigsaw puzzle, only this puzzle took almost 50 years to complete and not just by one scientist alone.

2. ATOM  Take a piece of chalk.  from a Greek word “atomos” which means indivisible  The smallest unit of an element that still has the properties of that element  1-inch line of gold = 88 million atoms

3. MOLECULE  Is a unit of a substance that can exist freely and posses all the properties of a given substance  a neutral chemically bonded group of atoms that acts as a unit  There are molecules that consist of only one atom, not group of them.

4. MOLECULES  Examples 1. He = O O O O = 4units/molecules each has 1 atom 2. O2 = = 2 molecules each contains 2 atoms 3. P = = 2 molecules each has 4 atoms

5. What is the true picture of an atom?  Today, the field ion microscope (by Erwin Mueller, 1956) and the Scanning Tunneling microscope (STM) (by the IBM scientists, 1980’s), give us clear images of the atom

6. DEVELOPMENT OF THE ATOMIC STRUCTURE  I. Early Ideas about the Atom - (460 – 370 B.C.) Democritus of Abdera, Greece, a famous teacher of “Atomists school of thought suggested the idea of the atoms using a piece of gold - Claimed that atoms are invisible, indestructible fundamental or smallest particles of matter - His theory was ignored because he lacked experimental proof to back it up.

7. DEVELOPMENT OF THE ATOMIC STRUCTURE  Plato and Aristotle - Both were prominent philosophers, demanded that atoms be shown to them. - Rejected the atomism claiming that this idea challenged the existence of God. - Said that you can divide anything endlessly.

8. DEVELOPMENT OF THE ATOMIC STRUCTURE  Later, atomic idea was picked up by other scientists like Galileo, Francis Bacon, Robert Boyle, and Isaac Newton who used the atomic idea to understand and explain visible events.

9. DEMOCRITUS’ ATOMIC MODEL

10. DEVELOPMENT OF THE ATOMIC STRUCTURE  II. DALTON’S ATOMIC THEORY - (1766-1844) John Dalton, an English school teacher at age 12 revived the idea of the atom after 2200 years. - Major Assumptions of DAT (1805) 1. Matter consists of tiny, indestructible particles called atoms. They remain unchanged during chemical reactions.

11. DEVELOPMENT OF THE ATOMIC STRUCTURE 2. Atoms of a particular element all have the same properties (size, shape, mass) different from those of other elements. 3. Atoms combine in simple/small number ratios when they form compounds. 4. A chem’l change involves the joining, separation or rearrangement of atoms in the compounds.

12. DEVELOPMENT OF THE ATOMIC STRUCTURE  Despite its flaws, this theory was accepted for it explained adequately 2 important laws of chemical combination. 1. The Law of Conservation of Mass 2. The Law of Constant/Definite Composition

13. DEVELOPMENT OF THE ATOMIC STRUCTURE  The Law of Conservation of Mass - States that no new atoms are gained or lost during a chem’l rxn, thus the mass during the rxn is unchanged. Atoms merely regrouped themselves. - Wood + O2 = ashes + smoke+ vapor (total mass)= (total mass)

14. DEVELOPMENT OF THE ATOMIC STRUCTURE  The Law of Constant/Definite Composition (Joseph Proust, 1794) - States that a pure compound always consists of the same elements combined in the same mass ratio. - Ex. H2O = 2H + 1O (2:1) NaCl = 1Na + 1Cl (1:1)

15. DALTON’S ATOMIC MODEL Dalton strengthened Democritus’ idea

16. REVISIONS OF THE D.A.T. 1. Atoms are divisible, consist of subatomic particles. 2. Atoms of the same elements have different masses. Isotopes 3. Atoms are not permanent. They can be converted to another atoms or be destroyed after certain nuclear processes. Ex. Ra - Rn - Po

17. ISOTOPES  are atoms of the same element but with different masses.  have the same number of protons/atomic no. but different number of neutrons/mass no.  Ex. H – protium, 0 neutron H - deuterium, 1 neutron H - tritium, 2 neutrons

18. YOUR TURN  10 – ITEM QUIZ

19. QUIZ DIRECTIONS: Answer the ff. correctly. 1. Draw Democritus’ atomic model. 2. Draw Dalton’s atomic model. 3. Name the 2 philosophers who rejected Democritus’ atomic idea. 4. Who is the father of atomic theory? 5. Who is the father of the modern atomic theory?

20. QUIZ 6. This law states that mass is conserved during a chemical rxn. 7. Atom comes from a Greek word ___ 8. Give an example of a one-atom molecule. 9. Give one microscope used to see atoms. 10. 1-inch line of gold has how many atoms?

21. Tomorrow Let’s talk about Thomson, Rutherford, and Bohr