Presentation on theme: "Counting units such as dozen or gross are commonly used to deal with large quantities of items. No matter what we are counting, a dozen means 12, whether."— Presentation transcript:
1 Counting units such as dozen or gross are commonly used to deal with large quantities of items. No matter what we are counting, a dozen means 12, whether we are counting oranges, pencils, or even elephants.
2 Review in your text – a mole Pages 83 – 87 definitions and practiceAvogadro’s number, rounded to 6.02 x 10 23is used to describe the amount of a substance so that chemists can determine the molar mass in one mole. Using the average atomic mass for each atom we can use dimensional analysis to determine the mass of 1 mole in grams for any substance .CHECK FOR UNDERSTANDING : COMPLETE PRACTICE PROBLEMS PG 85
3 What is a mole?The mole is a counting unit used by chemists to express the number of atoms or molecules in a sample.1 mole = 6.02 x1023 “things”1 mole of oranges contains 6.02 x1023 oranges.1 mole of helium gas contains 6.02 x1023 helium atoms.1 mole of water contains 6.02 x1023 water molecules.1 mole of sodium chloride contains 6.02 x1023 sodium chloride formula units.
4 Molecules vs. Formula Units The simplest unit of a molecular (covalent) compound is a molecule.Ionic compounds contain large numbers of ions held together in a lattice structure, they do not exist as single molecules. Instead, a formula unit represents the simplest ratio of atoms in an ionic compound.
5 Counting Atoms and Ions SubstanceFormulaNumber and Kind ofParticles in one MoleAtomic NitrogenN6.02 x1023 N atomsMolecular NitrogenN26.02 x1023 N2 molecules_______________ N atomsNitrogen DioxideNO26.02 x1023 NO2 molecules_______________ atomsSodium ChlorideNaCl6.02 x1023 NaCl formula units_______________ ionsSodium NitrideNa3N6.02 x1023 Na3N formula units_______________ Na+ ions_______________ N3– ions
6 Formula WeightFormula Weight – the sum of the atomic weights of the atoms in a chemical formula.Represents the mass of one moleculeMeasured in atomic mass units (amu)Calculate the formula weight of each of the following compounds:O2NaClCa3(PO4)2
7 Molar Mass Molar Mass – the mass in grams of one mole of a substance. By definition a mole of 12C has a mass of 12 grams.Because of this, the mass of a single atom of an element (in amu) is numerically equal to the mass (in grams) of 1 mole of that element.1 Mg atom = 24.3 amu1 mole of Mg atoms = 24.3 g1 H2O molecule = 18.0 amu1 mole of H2O molecules= 18.0 g1 O2 molecule = 32.0 amu1 mole of O2 molecules = 32.0 g
8 Why do we need the mole?Because atoms are extremely small and we usually deal with large amounts of them. Think about how many atoms are in 1 mole:602,000,000,000,000,000,000,000The mole is a useful tool for chemists because it provides a relationship between the number of atoms or molecules in a substance (which we cannot measure easily) and their mass (which we can measure easily).
9 Mole Conversions 1 mole = molar mass in grams (molar mass can be found using the periodic table).1 mole = 6.02 x1023 particles(particles can be atoms, molecules, or formula units)1 mole = Liters of any gas at STP(STP represents standard temperature and pressure conditions of 0 °C and 1 atmosphere respectively).