Chemist’s Dozen The Mole Lecture

TP Which of the following contains the smallest number of atoms? 25% 25% 25% 25% 1. 2. 3. 4. 187 g of liquid mercury, Hg 1400 u of uranium, U 6 1024 atoms of sodium, Na 2 mol of hydrogen gas, H2 For today … • Complete: Isotopes  atomic weight • Chemist’s dozen: The mole TP For our hypothetical class, average weight of a CH101 student is 144 lbs. Which of the following statements is true for this class? 0% 1. The weight of each student is 144 lbs 0% 2. No student weighs 144 lbs 0% 3. Neither of the statements is true. Average mass of an atom of K Two isotopes: K‐39 and K‐41 How many protons and how many neutrons in each? 1 Average mass of an atom of K Average mass of an atom of K Two isotopes: K‐39 and K‐41 Two isotopes: K‐39 and K‐41 K‐39 peak at 38.9637 u, height 933 K‐39 peak at 38.9637 u, height 933 K‐41 peak at 40.9618 u, height 67 K‐41 peak at 40.9618 u, height 67 Write and then evaluate the expression whose value is the average mass in u of an atom of K. The average mass in g of an atom of K is 38.9637 u 40.9618 u 39.098 u 39.098 u 39.098 1/12 12 g 1/NA 39.098 g / NA 6.4923 10 23 g Average mass of any atom Molar mass of any element The average mass of an atom of K is 39.098 g/NA Molar mass is the mass of The average mass of an atom of Br is 79.904 g/NA The average mass of an atom of K is 39.098 g/NA The average mass of an atom of H is 1.008 g/NA The molar mass of K is The average mass of any atom in g/NA is the number given on the periodic table. The molar mass of Br is 79.904 g A A “average” atoms of an element. 39.098 g/ A 39.098 g The molar mass of H is 1.008 g The molar mass of any element in g is the number given on the periodic table. 2 Atomic weight = magnitude of average mass The atomic weight of K is 39.098 no units! TP The periodic table indicates that “C” has a mass of 12.011. Which of the following statements is true? 1. 2. 3. 4. 5. 6. 7. All carbon atoms have mass 12.011 g All carbon atoms have mass 12.011 u No carbon atoms have mass 12.011 g No carbon atoms have mass 12.011 u 1 and 2 are correct 3 and 4 are correct None of the above The atomic weight of an element is the number given on the periodic table. 14% 14% 14% 14% 14% 14% 14% Quiz The molar mass of Cl is 35.453 g. 37Cl has a natural abundance of 24.24%. Which of the following statements is true? Terms to distinguish The atomic weight of Br is 79.904 The atomic weight of H is 1.008 0% 1. The mass of one atom of naturally occurring Cl is 35.453 g divided by Avogadro's number 0% 2. The mass of one atom of naturally occurring Cl cannot be 35.453 g divided by Avogadro's number. 0% 3. Neither of the statements is true. Relative atomic mass, r: ratio of mass of an isotope relative to mass of 1/12 of one 12C atom 13 r of C is 13.00335 unitless Atomic mass unit, u: 1/12 mass of one 12C atom 1u 1/12 12 g / A g / A 1.66054 10‒24 g Atomic weight: average of relative atomic masses of the isotopes of an element Atomic weight of C is 12.01 unitless Molar mass, : Mass in grams numerically equal to atomic weight; that is, the mass in grams of A “average atoms” of an element Molar mass of C is 12.01 g 3 Mole: Count by weighing Chemist’s dozen: mole  counting by weighing TP Which of the following contains the smallest number of atoms? 25% 25% 25% 25% 1. 2. 3. 4. 187 g of liquid mercury, Hg 1400 u of uranium, U 6 1024 atoms of sodium, Na 2 mol of hydrogen gas, H2 The mass in g of 1 mol of any element is called its molar mass Number of particles in 1 mol is NA 6.022140857 x 1023 Each of these amounts contains the same number of atoms Quiz Which of the following contains the largest number of atoms? 25% 25% 25% 25% 1. 2. 3. 4. 187 g of liquid mercury, Hg 1400 u of uranium, U 6 1024 atoms of sodium, Na 2 mol of hydrogen gas, H2 4