2. Chemistry What is chemistry? –Chemistry is the study of matter, what it is made of, and how it changes. What is matter? –Matter is anything that… Has mass. Takes up space.

3. What Is Matter? Pretty much everything –Element A pure substance that cannot be broken down to anything simpler by chemical or physical means. –Compound A pure substance that cannot be broken down to anything simpler by physical means. –Mixture Not a pure substance. Can be broken down by physical means.

4. What Is Matter? Is there a smallest particle of matter? –Philosophers and scientists have pondered this question since about 400 B.C. Our current theory: –An atom is the smallest particle of an element that retains all the properties of the element. –History of the modern atomic theory.

5. The History of the Atom How I Have Been Misunderstood

6. Who First Thought of Me? Democritus 400 BC Greek Philosopher credited with coming up with the idea of a single indivisible atom that was the smallest particle for all matter.

7. Have I been famous since then? No Why not? Nobody believed Democritus. He could not prove his idea. Who didn’t believe him? Other famous Greek dead dudes like…

8. History of the Atomic Theory By 1790, more accurate measurement lead to three major laws of nature: –Law of Conservation of Mass –Law of Definite Proportions (Constant Composition)-mass ratio –Law of Multiple Proportions (small whole numbers)

9. So what happened? The idea of the atom wallowed in obscurity for about 2000 years – not completely forgotten, but not believed, until…1808

10. John Dalton’s Atomic Theory 1808 –All matter is composed of small particles called atoms. –Atoms of a given element are identical in size, mass, and properties; atoms of different elements are different in size, mass, properties. –Atoms cannot be subdivided, created, or destroyed (law of conservation of mass).

11. John Dalton’s Atomic Theory –Atoms of different elements combine in simple whole number ratios to form chemical compounds (Law of definite proportions, Law of multiple proportions). –In chemical reactions, atoms are combined, separated, or rearranged (law of conservation of mass).

12. Main Parts of Daltons Theory All things are made of atoms. All atoms of the same element have the same size, mass, properties. Atoms can’t be created subdivided or destroyed. Atoms can combine or rearrange to form compounds.

13. Modern Atomic Theory All things are made of atoms. All atoms of the same element have the same size, mass, properties. Atoms can’t be created subdivided or destroyed. Atoms can combine or rearrange to form compounds.

14. How did we find out about the parts? JJ Thomson - 1897 discovered ELECTRONS Plum pudding model

15. Did we keep that model? No Ernie Rutherford – 1911 gold foil experiment - discovered NUCLEUS

16. Why don’t the electrons get sucked into the nucleus? Electrons have their own energy – Neils Bohr Only can absorb or give off energy in specific amounts called quanta

17. Parts of the Atom Information on the Periodic Table tells you about the number of each of the different parts of any given element. ---------------------

18. Atomic Number The atomic number is the number of protons in a an atom. –This determines what the element is. More or less protons would change it into a different completely element. –The number of protons = the total of the positive charges for an atom – BUT An Atom is neutral, so there can’t be an overall positive or negative charge. –Therefore, the number of protons also tells you … …the total of the negative charges for the atom.

19. Atomic Mass For a single atom: –Atomic mass = # of neutrons + # of protons in the atom. For a bunch of atoms = average mass of the atoms (protons and neutrons are the parts with mass ). Recall that atomic number tells you the number of protons. Use Atomic Number and Atomic Mass together to determine… … the total number of neutrons in the atom.