More About Formulas

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More About Formulas
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Formulas

• Tell the type number of atoms in a compound.
• Microscopic level imagine 1 atom, molecule, or
  formula unit.
• Formula gives atom ratios.
• Macroscopic level imagine working in the lab
• Formula gives mole ratio

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Formulas

• Ex 2H2O can mean
• 2 molecules of water
• 2 moles of water.
• 2H2O molecules have 4 hydrogen atoms 2 oxygen
  atoms.
• 2 Moles of H2O molecules have 4 moles of
  hydrogen atoms 2 moles of oxygen atoms.

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What can you say about CuSO4?5H2O?

• Its a hydrated salt.
• For every mole of CuSO4, there are 5 moles of
  water.
• If its heated, it dries out. The water goes
  into the air and youre left with the anhydrous
  salt, CuSO4.
• The mole ratio in the formula can be used to
  predict how much water would be given off by any
  size sample.
• If you had 2 moles of CuSO4?5H2O, how much water
  would you lose on heating?

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Percent Water in CuSO45H2O

• Step 1 Calculate the formula mass.
• Mass of salt Mass of water
• Percent (Part/Whole) X 100
• H2O Mass H2O/Formula Mass X 100

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Ionic vs. Covalent Formulas

• By looking at the type of atoms, we can decide if
  the substance is an ionic compound or a molecular
  (covalent) compound.

Molecular compounds have all nonmetals. Ionic
compounds usually have metal nonmetal.
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Empirical Formula

• Smallest whole number ratio of the elements in
  the compound.
• Ionic compounds have only empirical formulas.
• Covalent compounds have empirical and molecular
  formulas. They can be the same or different.

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Molecular Formulas

• For covalent (molecular) compounds.
• Give the exact composition of the molecule.
• Molecular compounds have both empirical and
  molecular formulas. They can be the same or
  different.

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Say everything you can about

• NaCl C6H6 C6H12O6
• CH4 CF4 BeSO4
• C8H18 KI C2H4Cl2
• CaBr2 CuSO4?5H2O

Covalent, molecular
Ionic, empirical
Covalent, molecular
Covalent, empir., molec?
Covalent, empirical, molecular?
Ionic, empirical
Ionic, empirical
Covalent, molecular
Covalent, molecular
Ionic, empirical
Ionic, empirical
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Say everything you can about

• PH3 C2H4 Al2O3
• SrI2 NF3 H2Se
• CH3OH SiO2 H2O2
• CCl4 XeF4 P4O10

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Relationship between empirical and molecular
formulas

• The molecular formula is a whole number multiple
  of the empirical formula.
• Molec. Formula n (Empirical Form.)
• n is a small whole number, which multiplies the
  subscripts. Sometimes, n 1.

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Molecular Formula

• If you know the empirical formula and the molar
  mass, you can find the molecular formula.
• Step 1 Find the mass of the empirical formula.
• Step 2 Molar mass ? Empirical mass small
  whole number, n
• Step 3 Multiply the subscripts in the empirical
  formula by n.

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Finding Molecular Formulas

• Find the molecular formula for the substance
  whose empirical formula is CH and whose molar
  mass 78.0 g
• Step 1 Empirical mass 13.0 g
• Step 2 Molar mass n 78.0/13.0
• n 6.
• Step 3 6 X subscripts in CH C6H6.

Empirical mass