THE MOLE CONCEPT

Objects are measured by counting or by weight (mass) It’s easier to measure large objects by counting –Elephants, cars, eggs It’s easier to measure small objects by weight (mass) –Nails, rice, pellets THE MOLE CONCEPT

Chemist handle chemicals in two ways –Chemicals that we can see and measure in the lab 16 grams of CH 4 or 32 grams of O 2 –Molecules that we in our heads that move and combine to form new products CH O 2 → CO H 2 O THE MOLE CONCEPT

Through experiments we can find the relative mass of molecules –One molecule of CH 4 has a mass of 16 a.m.u. (atomic mass units) –One molecule of O 2 has a mass of 32 a.m.u. Knowing the mass of just one molecule is not very helpful in the lab because one molecule is just too small. THE MOLE CONCEPT

We can measure 16 grams of CH 4 and 32 grams of O 2 These amounts are called the molecular (molar) mass in grams. When you measure out one gram molecular mass of a substance, you have weighed out the same number of molecules!! THE MOLE CONCEPT

Substance Gram Molecular Mass (grams) Number of Particles (Molecules) CH 4 16 g6.02 x O2O2 32 g6.02 x CO 2 44 g6.02 x H2OH2O18 g6.02 x 10 23

THE DOZEN ANALOGY Coin Mass of one coin Dozen Mass Number of Coins Penny2 g24 g12 pennies Nickel4 g48 g12 nickels Dime1.5 g18 g12 dimes Quarter7 g84 g12 quarters

CH O 2 → CO H 2 O Since each gram molecular mass of a substance contains the same number of particles (molecules). From the equation above we know that one molecule of CH 4 will combine with 2 molecules of O 2 to produce one molecule of CO 2 and 2 molecules of H 2 O. THE MOLE CONCEPT

The gram molecular mass is a bridge between the measurements we made in lab (what we can see) and the way that individual molecules (that we cannot see) react. We shorten the name of gram molecular mass to the word MOLE –Scientists have found that a mole contains 6.02 x molecules –This is 602,000,000,000,000,000,000,000 molecules!! THE MOLE CONCEPT

Defining the Mole Definition of the mole (mol) –One mole is the amount of any substance that contains the same number of units as the number of atoms in exactly 12 grams of Carbon-12 –1 mole of any substance = 6.02 x units of that substance. (unit = molecules, formula units, or atoms) –6.02 x is known as Avogadro’s Number

The central relationship between the mass of one atom and the mass of one mole of those atoms is the atomic mass of an element obtained from the periodic table and is expressed in atomic mass units (a.m.u.) The a.m.u. is numerically the same as the mass of one mole of atoms of the element expressed in grams Defining the Mole

1 Fe atom has a mass of a.m.u. 1 mole of Fe atoms has a mass of grams grams of Fe contains 6.02 x atoms Defining the Mole

A similar relationship holds for compounds. The molecular mass (or formula units) of a compound expressed in atomic mass units is numerically the same as one mole of the compound expressed in grams Defining the Mole

1 molecule of H 2 O has a molecular mass of a.m.u. 1 mole of H 2 O has a mass of grams grams of H 2 O has 6.02 x molecules Defining the Mole

A mole of any ordinary object is a staggering amount, however, atoms, molecules are not ordinary objects. They are much smaller than ordinary objects. Therefore 1 mole is not such a staggering amount! THE MOLE CONCEPT

1 mole of any substance = 6.02 x units of that substance. If you spread 1 mole of un-popped popcorn kernels across the USA the entire country would be covered in popcorn to a depth of over 9 miles. If 1 mole of marbles were spread over the surface of the Earth, our planet would be covered by a 50-mile thick layer of marbles. 1 mole of soft drink cans would cover the surface of the earth to a depth of over 200 miles IMAGINE:

WE DIG CHEMISTRY