Everything is within walking distance if you have the time.- Steven Wright -

DALTON’S ATOMIC THEORY  ALL MATTER IS COMPOSED OF ATOMS.  ATOMS CANNOT BE MADE OR DESTROYED (IN AN ORDINARY CHEMICAL REACTION).  ALL ATOMS OF THE SAME ELEMENT ARE IDENTICAL.  DIFFERENT ELEMENTS WOULD HAVE DIFFERENT TYPES OF ATOMS.  CHEMICAL REACTIONS OCCUR WHEN ATOMS ARE REARRANGED.  COMPOUNDS ARE FORMED FROM A COMBINATION OF TWO OR MORE ELEMENTS.

WE CAN REPRESENT CHEMICAL COMPOUNDS USING SYMBOLS FOR THE ELEMENTS WITH SUBSCRIPTS AFTER THE SYMBOL REPRESENTING THE NUMBER OF ATOMS IN THE COMPOUND. FOR EXAMPLE: H 2 SO 4 SULFURIC ACID # HYDROGEN ATOMS# OXYGEN ATOMS ONE SULFUR ATOM

WE CAN ALSO USE OUR SYMBOLS TO REPRESENT CHEMICAL REACTIONS. FOR EXAMPLE: 3H 2 O + 2Fe  Fe 2 O 3 + 3H 2 THE ABOVE EQUATION TELLS YOU THAT 3 WATER MOLECULES WILL REACT WITH 2 IRON ATOMS TO YIELD ONE RUST MOLECULE AND 3 HYDROGEN MOLECULES. THE SUBSTANCES ON THE LEFT ARE REACTANTS, AND THE SUBSTANCES ON THE RIGHT ARE PRODUCTS.

3H 2 O + 2Fe  Fe 2 O 3 + 3H 2 THE EQUATION IS BALANCED. IN OTHER WORDS, THERE ARE THE SAME NUMBER OF ATOMS OF EACH TYPE ON THE LEFT AS ON THE RIGHT. MATTER IS NEITHER CREATED OR DESTROYED IN A CHEMICAL REACTION. IT IS JUST REARRANGED. THIS IS THE LAW OF CONSERVATION OF MASS.

NOW, WE WOULD LIKE TO BE ABLE TO CALCULATE HOW MANY ATOMS OF EACH TYPE ARE INVOLVED IN DIFFERENT SUBSTANCES. WE CAN FIGURE OUT HOW MANY GRAMS OF EACH SUBSTANCE ARE INVOLVED IN DIFFERENT COMPOUNDS. BUT, WE CAN’T WEIGH INDIVIDUAL ATOMS. 1 ATOMIC MASS UNIT = 1.67 X grams ROUTINE MASS DETERMINATIONS ARE VERY DIFFICULT MUCH BELOW grams.

WHAT WE CAN DO IS TO WORK WITH LARGER QUANTITIES OF MATTER THAT CONTAIN EQUAL NUMBERS OF ATOMS. IF YOU LOOK AT THE ATOMIC MASSES GIVEN ON THE PERIODIC TABLE, IT TURNS OUT THAT IF YOU TAKE THESE MASSES IN GRAMS, THEY WILL CONTAIN THE SAME NUMBER OF ATOMS. THIS NUMBER IS REFERRED TO AS AVOGADRO’S NUMBER OR ONE MOLE X = 1 mole

FOR EXAMPLE, IF WE KNOW THAT 2 GRAMS OF HYDROGEN REACT WITH 16 GRAMS OF OXYGEN TO FORM WATER, 1 gram OF HYDROGEN = 1 mole HYDROGEN SO, 2 g H = 2 moles 16 grams OXYGEN = 1 mole OXYGEN IF 2 moles H REACTS WITH 1 mole OXYGEN, 2 atoms of H REACT WITH 1 atom OXYGEN, SO THE FORMULA WOULD BE H 2 O

ANOTHER WAY YOU COULD LOOK AT THAT IS: 2 X (6.023 X ) H + (6.023 x ) O to give water Or dividing by (6.023 x ), 2 H + 1 O gives water THE ATOMIC WEIGHT (MASS) IN GRAMS CONTAINS 1 MOLE OF ATOMS OF THAT ELEMENT. 1 gram H16 gram O

THIS CONCEPT IS GOING TO ALLOW US TO WORK WITH AND DETERMINE CHEMICAL FORMULAS AND TO UNDERSTAND CHEMICAL REACTIONS. WE CAN DEAL WITH KNOWN NUMBERS OF ATOMS WITHOUT HAVING TO DETERMINE OR WEIGH INDIVIDUAL ATOMS. IN THE SI SYSTEM, A MOLE IS DEFINED AS THE NUMBER OF ATOMS IN EXACTLY 12 GRAMS OF CARBON-12.

MOLE CALCULATIONS FIRST, LET’S PRACTICE CALCULATING MOLAR MASS (the mass of one mole of a substance in grams). CALCULATE THE MOLAR MASS OF CARBON DIOXIDE, CO 2 The atomic mass of C = The atomic mass of O = The molar mass of CO 2 = g/mol + 2(16.00 g/mol) = = g/mol - GOOD REF.

CALCULATE THE MOLAR MASS OF Fe 2 O 3 Atomic mass of Fe = g/mol Atomic mass of O = g/mol Molar mass of Fe 2 O 3 = 2(55.85) + 3(16.00) = = g/mol Another good online tutorial - calculation.htmlhttp:// calculation.html

HOW MANY GRAMS OF H 2 SO 4 ARE IN 3 MOLES? Atomic mass H = 1.01 g/mol Atomic mass S = g/mol Atomic mass O = g/mol Molar mass H 2 SO 4 = 2(1.01) (16.00) = = g/mole Mass in 3 moles = 3 moles x g/mole = g

HOW MANY GRAMS OF ACETIC ACID, C 2 H 4 O 2, ARE IN 0.3 MOLE? Atomic mass C = g/mole Atomic mass H = 1.01 g/mole Atomic mass O = g/mole Molar mass = 2(12.01) + 4(1.01) + 2(16.00) = = g/mole Grams in 0.3 mole = 0.3 mole x g/mole = g NOTE: Sometimes molar mass is called formula mass.