The counting unit of chemistry The Mole The counting unit of chemistry

Why the mole? Atoms and molecules are too small to keep track of individually! It is easier to count them in packages. Same concept as the dozen! A mole is a package of many, many, many particles (like atoms or molecules). How many exactly?

More Mole Fun Facts 1 mole (abbreviated “mol”) = 6.0221367 x 1023 representative particles representative particles = atoms, ions, electrons, molecules, or formula units We can just round the mole to 3 sig. figs: 6.02 x 1023 particles 6.02 x 1023 is called “Avogadro’s Number”

But, a gallon of water contains 210 moles of water molecules! A mole is a lot….. The mole is so many particles, it is really only useful for counting particles of matter. There is not a mole of people on earth… There is not a mole of pennies on earth… There is not a mole of stars in the Milky Way There might be a mole of stars in the universe…… But, a gallon of water contains 210 moles of water molecules!

What are representative particles? The fundamental types of particles that make up pure substances (elements and compounds) Some pure substances are made of atoms (for examples, all metals and noble gases) Some pure substances are made of molecules (for example, all covalent compounds, like water) Some pure substances are made of formula units (for example, all ionic compounds, like table salt)

Representative particles…. For now, it does not matter what type of representative particle a pure substance is made of. I will tell you. All you need to know is that if you have a mole of a pure substance, you have 6.02 x 1023 of its particles. So: a mole of sugar is 6.02 x 1023 molecules a mole of helium is 6.02 x 1023 atoms

Converting Moles  Rep. Particles Just use D. A. and the conversion factor 1 mol = 6.02 x 1023 rep. particles Ex 1) 5.0 moles of Na = _____ atoms Na? Ex 2) 3.45 x 1023 molec. of CH2O = _____ moles CH2O?

Whiteboard assignment Groups of 2 – write both of your names and the station number on your paper. Perform 4 mole  rep. particle conversions (highlighted at each station). Show all D.A work. Each box of grid must have a number, unit, and a label. Calculate to sig. figs. and put a unit and label on each answer too.

6.02 x 1023 Why this number?? It is based on the number of particles in 12 grams of pure 12C 12 g 12C .001 kg 1 amu 1 atom 12C 1 g 1.6605 x 10-27 kg 12 amu = 6.02 x 1023 atoms 12C We’ll come back to this relationship later….

Moles  Mass We do not measure out substances in terms of moles, but rather, in terms of mass (grams). There is a simple relationship between the amount of moles and the mass of an element….it can be found right on the periodic table!

Relationship between Relative Atomic Mass (Ar) and Molar Mass 6 C 12.01 The relative atomic mass of an atom of an element in amus is also the molar mass of an entire mole of those atoms in grams.

Just use D. A. and the conversion factor Converting Mole  Mass Just use D. A. and the conversion factor 1 mol = molar mass (g) Ex 1) 45.2 g of Zn = _____ moles Zn Ex 2) 0.568 moles Ag = _____ grams Ag

Putting it all together… molar mass 6.02 x 1023 grams  moles  rep. particles Ex 1) Convert 50.0 g of Mg to atoms: Ex 2) Convert 7.200 x 1024 atoms of He to grams:

Calculating Molar Masses of Compounds Just add together the molar masses of all the elements in the compound (by Conservation of Mass). Distribute through the parentheses when necessary. Ex 1) CCl2F2 Ex 2) MgCO3 Ex 3) (NH4)3PO4 Ex 4) Sn3(PO4)4

grams  moles  rep. particles Try this now….. molar mass 6.02 x 1023 grams  moles  rep. particles Convert 5.27 x 1024 formula units of Sn3(PO4)4 to grams.