Chapter 3 Atoms: The Building Blocks of Matter

I. The Atom *Matter: anything that has mass and volume *Indirect Evidence: evidence you get without actually seeing or touching the object

-Greek Model (Democritus) *atom: smallest particle of an element that has the prop of the element ~atomos: meaning not to be cut

-Dalton’s Atomic Theory 1. All elements are composed of atoms 2. Atoms of the same element are exactly alike

3. Atoms of diff. elements are diff. 4. Compounds are formed by joining of atoms of 2 or more elements

5. In Chem Rxn’s, atoms are combined, separated, or rearranged. -Are exceptions: 1. Atoms are divisible 2. Given elements can have atoms with diff masses (isotopes)

*Law of Conservation of Mass: pg 66 *Law of Multiple Proportions: pg 66 *Law of definite proportions: pg 66

II. The Structure of the Atom -Thomson’s Model: ~Plumb Pudding *Electrons: - charge

~Cathode Ray (pg 70) *Cathode: conn to the neg *Anode: conn to the pos

-Rutherford’s Model ~Gold Foil Experiment

~Inferences made about atomic struct 1. e- small 2. neg 3. must have a + charge to make an atom neutral 4. Atom mass must come from somewhere else??

~the atom was mostly empty space with a dense, positively charged nucleus in the center. *Nucleus: the center of the atom *Nuclear Force: hold nuclei together  Like charges “+/+” *Electrostatic (Electromagnetic): holds opposite charges together “e-/+”

-Bohr Model ~electrons move in definite orbits around the nucleus

-Wave Model (Today accepted model) ~electrons don’t move about in a definite path ~probable location is based on how much nrg the electron has

-Subatomic particles *smaller than the atom

Electrons Electrons orbit around an atom. In this picture, they are the small yellow bits. They have a negative charge. They are lighter than protons or neutrons.

They are positively charged. Are located in the nucleus. In this picture, the protons are the blue pieces in the center of the atom.

Neutrons are neither positive nor negative. Neutrons are in the nucleus of an atom. In this picture, neutrons are the purple pieces in the center of the atom.

mass (amu) charge location ~proton:1+nucleus ~neutron: 1+/- nucleus ~electron: 1/1836- e- cloud

SEE HISTORY OF THE ATOM WEBSITE cture/chemistry/chapter_8/pages/history_ of_atom.html dels.html emo/units/LR301.html#J.J.Thomson

III. Counting Atoms *Atomic Mass Unit (amu): measures mass of subatomic part. -?? Where does it come from?? 1/12 mass of a C-12 atom

-Atomic # *number of + in the nucl ~identifies the element ~never chngs

-Mass # and Atomic Mass *sum of the + and neutrons in its nucleus -Isotopes *same # of +, but diff # of neutrons(same elem, diff mass) *Nuclide: any isotope of any element EX: table 3-3 pg 77

-Isotopes of H (pg 76) 1. Protium: most common 1+, 1e-, 0+/- mass# = 1 2. Deuterium: 1+, 1e-, 1+/- mass# = 2 3. Tritium: 1+, 1e-, 2+/- mass# = 3

isotope notation 1. mass # H : Nuclear symbol atomic# pg: 77 2.Hydrogen - mass # pg 80

*Aver Atomic mass: aver of the masses of all the atoms in the sample. (that’s why Atomic mass is not a nice numb) ~mass # - atomic# = #of neutrons

*Mole: # of particles in 12 grams of C- 12 pg 81 *Avogadro’s #: # of particles in 1 mole of substance X atoms mole

*Molar Mass: mass of 1 mole of pure substance units---- g/mole -Gram/Mole Conversion Examples