Chapter 4.1 & 2 - General Chemistry, PDF

GENERAL CHEMISTRY General, Organic and Biochemistry 11th Edition Copyright The McGraw-Hil...

GENERAL CHEMISTRY General, Organic and Biochemistry 11th Edition Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4.1 The Mole Concept and Atoms Atoms are exceedingly small 1 – Unit of measurement for mass of an atom is atomic mass unit (amu) – unit of measure for the mass of atoms carbon-12 assigned the mass of exactly 12 amu 1 amu = 1.66  10-24 g Periodic table gives atomic weights in amu  Mass of Atoms 4.1 The Mole Concept and What is the atomic weight of one atom of fluorine? Answer: 19.00 amu What would be the mass of this one atom in grams? Atoms 19.00 amu F 1.661 10 -24 g 3.156 10 23 g F   F atom 1 amu F F atom Chemists usually work with much larger quantities – It is more convenient to work with grams than amu when using larger quantities 4.1 The Mole Concept and The Mole and Avogadro’s Number A practical unit for defining a collection of atoms is the mole Atoms 1 mole of atoms = 6.022  1023 atoms This is called Avogadro’s number – This has provided the basis for the concept of the mole  The Mole 4.1 The Mole Concept and To make this connection we must define the mole as a counting unit 2 – The mole is abbreviated mol Atoms A mole is simply a unit that defines an amount of something – Dozen defines 12 – Gross defines 144  Atomic Mass 4.1 The Mole Concept and The atomic mass of one atom of an element corresponds to: – The average mass of a single atom in amu Atoms – The mass of a mole of atoms in grams – 1 atom of F is 19.00 amu 19.00 amu/atom F – 1 mole of F is 19.00 g 19.00 g/mole F 24 19.00 amu F 1.66  10 g F 6.022 10 atom F 23   1 atom F 1 amu F 1 mol F =19.00 g F/mol F or 19.00 g/mol F  Calculating Atoms, Moles, and Mass 4.1 The Mole Concept and We use the following conversion factors: 2 Density converts between grams and milliliters Atoms Atomic mass unit converts between amu and grams Avogadro’s number converts between moles and number of atoms Molar mass converts between grams and moles  Calculating Atoms, Moles, and Mass 4.1 The Mole Concept and Calculate the number of mol of S represented by 1.81 x 1024 atoms of S. We know the relationship between moles and Atoms atoms is given by Avogadro’s Number: 1 mol S = 6.022 x 1023 atoms S We can write this as two possible fractions, and choose the one appropriate to this problem 1 mol S 6.022 x 1023 atoms S 6.022 x 1023 atoms S 1 mol S  Calculating Atoms, Moles, and Mass 4.1 The Mole Concept and Calculate the number of mol of S represented by 1.81 x 1024 atoms of S. Now we can set up the problem with the Atoms starting unit (atoms) in the denominator of the conversion factor. 1.81 x 1024 atoms S x 1 mol S 6.022 x 1023 atoms S = 3.01 mol S  Calculating Atoms, Moles, and Mass 4.1 The Mole Concept and What is the mass, in g, of 3.01 mol of S? We know the relationship between moles and grams by the molar mass of S: Atoms 1 mol S = 32.06 g S We can write this as two possible fractions, and choose the one appropriate to this problem 1 mol S 32.06 g S 32.06 g S 1 mol S  Calculating Atoms, Moles, and Mass 4.1 The Mole Concept and What is the mass, in g, of 3.01 mol of S? Now we can set up the problem with the starting unit (mol) in the denominator of the Atoms conversion factor. 3.01 mol S x 32.06 g S = 96.5 g S 1 mol S  Strategy for Calculations 4.1 The Mole Concept and Calculate the number of atoms of S in 1.00 g of S. Map out a pattern for the required conversion Atoms Two conversions are required: – Step 1: Convert g to mol using Molar Mass of S – Step 2: Convert mol to atoms using Avogadro’s Number  Strategy for Calculations 4.1 The Mole Concept and Calculate the number of atoms of S in 1.00 g of S. Atoms 1 mol S 6.022 x 1023 atoms S 1.00 g S x x 32.06 g S 1 mol S Molar Mass Avogadro’s Number = 1.88 x 1022 atoms S  Practice Calculations 4.1 The Mole Concept and 1. Calculate the number of atoms in 1.7 moles of boron. 2. Find the mass in grams of 2.5 mol Na Atoms (sodium). 3. Calculate the number of atoms in 5.0 g aluminum. 4. Calculate the mass of 5,000,000 atoms of Au (gold) 4.1 The Mole Concept and Interconversion Between Moles, Particles, and Grams Atoms  4.2 The Chemical Formula, Formula Weight, and Molar Mass 3 Chemical formula - a combination of symbols of the various elements that make up the compound Formula unit - the smallest collection of atoms that provide two important pieces of information – The identity of the atoms or ions – The relative number of each type of atom or ion 4.2 The Chemical Formula, Formula Weight and Molar Mass Chemical Formula Consider the following formulas: H2 – 2 atoms of hydrogen are chemically bonded forming diatomic hydrogen, subscript 2 H2O – 2 atoms of hydrogen and 1 atom of oxygen, lack of subscript means one atom NaCl – 1 ion each of sodium and chlorine Ca(OH)2 – 1 ion of calcium and 2 ions of the hydroxide polyatomic ion, subscript outside parentheses applies to all atoms inside 4.2 The Chemical Formula, Formula Weight and Molar Mass Chemical Formula Consider the following formulas: (NH4)3SO4 – 2 ammonium ions and 1 sulfate ion – Ammonium ion contains 1 nitrogen and 4 hydrogen – Sulfate ion contains 1 sulfur and 4 oxygen – Compound contains 2 N, 8 H, 1 S, and 4 O CuSO4.5H2O – This is an example of a hydrate - compounds containing one or more water molecules as an integral part of their structure – 5 units of water with 1 CuSO4  Comparison of Hydrated and 4.2 The Chemical Formula, Formula Weight and Molar Mass Anhydrous Copper Sulfate Hydrated copper sulfate Anhydrous copper sulfate Marked color difference illustrates the fact that these are different compounds Formula Weight and Molar Mass Formula Weight and Molar Mass 4.2 The Chemical Formula, Formula weight - the sum of the atomic weights of all atoms in the compound as represented by its correct formula 4 – expressed in amu What is the formula weight of H2O? – 16.00 amu + 2(1.008 amu) = 18.02 amu Molar mass – mass of a mole of compound in grams / mole – Numerically equal to the formula weight in amu What is the molar mass of H2O? – 18.02 g/mol H2O  Formula Unit 4.2 The Chemical Formula, Formula Formula unit – smallest Weight and Molar Mass collection of atoms from which the formula of a compound can be established When calculating the formula weight (or molar mass) of an ionic compound, the smallest unit of the crystal is used What is the molar mass of (NH4)3PO4? 3(N amu) + 12(H amu) + P amu + 4(O amu)= 3(14.01) + 12(1.008) + 30.97 + 4(16.00)= 149.10 g/mol (NH4)3PO4 4.2 The Chemical Formula, Formula Weight and Molar Mass Molar Mass Molar mass - The mass in grams of 1 mole of atoms What is the molar mass of carbon? 12.01 g/mol C This means a mole of Carbon atoms (6.022  1023) would have a mass of 12.01 g One mole of any element contains the same number of atoms, 6.022  1023 (Avogadro’s number)