Ch 4

• Atoms are exceedingly small
• Atomic mass unit (amu)


  Unit of measurement for mass of an atom
• Carbon-12 is assigned the mass of exactly 12 amu
• Periodic table gives atomic masses in amu
• Atomic mass of one atom of fluorine

  18.998 amu
• Chemists usually work with much larger quantities
• It is more convenient to work with grams than amu when using larger quantities
• Mole

  Practical unit for defining a collection of atoms
• 1 mole of atoms

  Avogadro's number
• Avogadro's number is the basis for the concept of the mole
• Mole


  A counting unit
• The mole is abbreviated mol
• A mole is simply a unit that defines an amount of something
• Dozen


  Defines 12
• Gross


  Defines 144
• Atomic mass

  One atom of an element corresponds to average mass of a single atom in amu
• Molar mass

  One mole of an element corresponds to the mass of a mole of atoms in grams
• 1 atom of F is 18.998 amu
• 1 mole of F is 18.998 g
• Density

  Converts between grams and milliliters
• 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
• 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, and the relative number of each type of atom or ion
• Chemical formula examples

  • H2 - 2 atoms of hydrogen
  • H2O - 2 atoms of hydrogen and 1 atom of oxygen
  • NaCl - 1 ion each of sodium and chlorine
  • Ca(OH)2 - 1 ion of calcium and 2 ions of the hydroxide polyatomic ion
• Chemical formula examples

  • (NH4)2SO4 - 2 ammonium ions and 1 sulfate ion
  • CuSO4.5H2O - an example of a hydrate, containing 5 units of water with 1 CuSO4
• Hydrates are compounds containing one or more water molecules as an integral part of their structure
• Formula mass

  The sum of the atomic masses of all atoms in the compound as represented by its formula, expressed in amu
• The formula mass of H2O is 18.015 amu
• Molar mass

  Mass of a mole of compound in grams/mole, numerically equal to the formula mass in amu
• The molar mass of H2O is 18.015 g/mol H2O
• Formula unit

  The smallest collection of atoms from which the formula of a compound can be established
• Molar mass

  The mass in grams of 1 mole of atoms
• The molar mass of carbon is 12.010 g/mol C
• Chemical equation

  Shorthand notation of a chemical reaction, describing all the substances that react and all the products that form, physical states, and experimental conditions
• Reactants

  The starting materials that undergo change in the reaction
• Products

  The substances produced by the reaction
• The identity of products and reactants must be specified using chemical symbols
• Reactants are written to the left of the reaction arrow and products are written to the right