Atomic Structure PSC Chapter 3

Atomic Theory of Matter Evidence of atoms Law of Definite Proportions Law of Conservation of Mass Law of Multiple Proportions Dalton’s Atomic Theory

Evidence of atoms 400 BC – Greeks Atomic Theory 18th Century Europe -Democritus all matter is composed of small particles called atoms Atomos - indivisible 18th Century Europe Experimental results support the existence of atoms

Basic Components of the Theory… Law of Definite Proportions For any sample, a compound always has the same composition A given compound contains the same elems. in the same proportions by mass For example: NaCl is always 39.34% Na and 60.66% Cl by mass

Basic Components of the Theory… Law of Conservation of Mass For any chemical reaction, the mass of the products equals the mass of the reactants. Matter is neither created nor destroyed. For example: 32.07 amu of S combines with 32.00 amu of O2, 64.07 amu of sulfur dioxide.

Basic Components of the Theory… Law of Multiple Proportions For any compounds formed by the same two elements, the mass ratio of one of the elems. that combines w/ a fixed mass of another elem. can be expressed in small whole numbers For example: H2O and H2O2

Dalton’s Atomic Theory All matter is made of indivisible & indestructible atoms. All atoms of the same element are identical in their physical and chemical properties. Atoms of different elements differ in their physical & chemical properties

Dalton’s Atomic Theory 4. When atoms combine, they unite in simple, whole-number ratios to form compounds. 5. Chemical reactions consist of the combination, separation, or rearrangement of atoms.

Assignment Do p. 78 #1-9 Be ready for the quiz next time!