1. Elements vs. Compounds Elements can NOT be chemically broken down to a simpler substance, compounds can. (Ex. 2H 2 O  2H 2 + O 2 ) Most materials are MIXTURES of elements and/or compounds

2. Law of Constant Composition A given compound always contains the same proportions (by mass and by number) of its elements This means a given compound always has the same composition, regardless of where it came from.

3. Dalton’s Atomic Theory Elements are made of tiny particles called ATOMS All atoms of a given element are identical***** The atoms of a given element are different from those of any other element

4. Atomic Theory Cont’d Atoms of one element can combine with atoms of other elements to form compounds. A given compound always has the same relative numbers and types of atoms. Atoms are indivisible in chemical processes. That is, atoms are not created or destroyed in chemical reactions. A chemical reaction simply changes the way atoms are grouped together.

5. Chemical Formulas A formula describes how a compound is composed in terms of atoms (how many and which) How many of each atom are in: Na 2 CO 3 (NH 4 ) 3 PO 4

6. ATOMS

7. Make Up of the Atom Protons – (p + ) –Defines the element –Is the whole number on the periodic table –Have a positive charge –Has a mass of 1 amu (atomic mass unit) How many protons does Carbon have? How many protons does Iron have? How many protons does Ununnilium have? What element has 35 protons?

8. Make Up of Atoms Neutrons – (n 0 ) –Have no charge (neutral) –Have a mass of ~1 amu –Contribute to the total mass of an atom –Define the isotope of an atom –# neutrons = atomic mass – atomic # (# of p + ) How many neutrons does Carbon-12 have? How many neutrons does Carbon 14 have? How many neutrons does Uranium-238 have?

9. Make Up of Atom Electrons – (e - ) –Have a negative charge –Equal numbers as protons in NEUTRAL atoms –Gained, lost, or shared in CHEMICAL REACTIONS –Have a mass of 1/1836 th of a proton (negligible!) How many electrons does Carbon have? How many electrons does Fluorine have?

10. Make Up Of Atom Protons and Neutrons are in the center of the atom. Electrons are whizzing around the nucleus

11. Empty Space There is a LOT of empty space is in between the nucleus and the electrons If the nucleus was a fly on the 50 yard line of a football stadium, the electrons would be in the outermost seats…

12. Chemical v. Nuclear Reactions Chemical reactions: –Electrons are involved (exchanged or shared) –Atoms are rearranged, but stay as the same atom. –What we will be studying most this year Nuclear reactions: –Nuclei (protons and neutrons) are involved and changed. –Atoms become different elements by losing or gaining protons.