2AP CHEMISTRY Significant Figures The number of significant figures is the number of digits known with certainty plus one uncertain digit.(Example: g means we are sure the mass is _______ but we are uncertain about the nearest g.)•Final calculations are only as significant as the least significant measurement.2.240 g
3AP CHEMISTRY Sig. Fig. Rules Nonzero digits are significant. (Nonzero Rule)Example: 2.45 cm =________2) Zeros between sig. figs. are significant. (Straddle Rule)Example: 2.03 cm=_________3) Zeros at the end of the number and after a decimal point are significant. (Righty-Righty Rule)Example: cm=_________3 s.f3 s.f4 s.f
4Example: 10,300 grams = _____________ AP CHEMISTRY4) Zeros at the end of a number before a decimal point are ambiguous…In some cases, a bar will be placed over a zero to eliminate the ambiguity or the number will be written in scientific notation. (Bar Rule)Example: 10,300 grams = _____________1.030 x 104 g = _________5) If a number is known for certain, it is said to contain an infinite number of sig. figs. (Counting Rule)Example: 60 seconds =1 minuteat least 3 s.f.4 s.f(60 is known to ∞ # of s.f.)
5Significant Figures in Calculations AP CHEMISTRYSignificant Figures in Calculations• Multiplication and Division:- Report to the least number of significant figuresExample: cm x 5.2 cm = _______• Addition and Subtraction:- Report to the least number of decimal placesExample: g – g = _______32 cm219.1 g
6AP CHEMISTRY Density • Density= mass/volume -Density can be used as a “conversion factor” as well!massDensityvolume
7AP CHEMISTRY Counting p+, no and e- • Protons = Atomic Number Electrons = protons (in a neutral atom)Neutrons = Mass # - protonsMass Number = protons + neutronsGaining electrons gives an atom a (-) charge.Losing electrons gives an atom a (+) charge.
8AP CHEMISTRY Naming Compounds Molecules– Contains only 2 nonmetals; covalent bonding.General FormatPrefix (except mono)-name 1st element prefix-name 2nd element ending in –ide
10AP CHEMISTRY Naming Compounds Cation Name Anion Name Ionic– Starts with metallic cation (or NH4+); ionic bonding.General FormatCation Name Anion NameYou will have to memorize the cation and anion symbols & charges!We will have a quiz over them later!
11AP CHEMISTRYNaming CompoundsAcids– Starts with “H”
12Example: C3H8 + __O2 __CO2 + __H2O AP CHEMISTRYBalancing EquationsYou can only change coefficients!Example: C3H8 + __O2 __CO2 + __H2O534
13AP CHEMISTRY Percent Composition AW stands for the atomic weight of the atom from the periodic table.FW stands for the formula weight of the compound.
14AP CHEMISTRY Empirical Formulas Helpful Rhyme: % to mass, mass to mole, divide by small, times ’til whole.
15Stoichiometry Conversion Factors AP CHEMISTRYStoichiometry Conversion Factors1 mole = 22.4 L (at STP) = 6.02 x 1023 particles = FW (grams)These conversions will take up to 3 steps and no more!Always convert to moles of given first!
16Stoichiometry Conversions- (gram to gram) AP CHEMISTRYStoichiometry Conversions- (gram to gram)
17Limiting Reagent (or Reactant) AP CHEMISTRYLimiting Reagent (or Reactant)The reactant that runs out first “limits” the amount of product that can be formed.Stoichiometry conversions can be done to determine which substance is the limiting reagent.
18AP CHEMISTRY% YieldThe amount of product predicted from stoichiometry taking into account limiting reagents is called the theoretical yield.The percent yield relates the actual yield (amount of material recovered in the laboratory) to the theoretical yield: