• Describe two fundamental types of chemical bonding.
• Compare properties of ionic compounds and covalent compounds.

• Classify compounds as ionic or covalent.
• Define and distinguish between empirical formulas, molecular formulas, and structural formulas for compounds.
• Define, calculate, and relate formula weights and molecular weights.
• Name and write the formulas for

• polyatomic ions
• binary compounds(covalent or ionic)
• simple ionic compounds
• inorganic acids
• addition compounds
• Explain the mole concept, and convert between grams, moles, and atoms and molecules.
• Determine mass percent composition of a sample from experimental data.
• Determine mass percent composition of a compound from its formula.
• Determine empirical formula of a compound from its mass percent composition.

• Review the names and symbols of elements. (Use this interactive periodic table for drill.)
• Review prediction of charges for the most common ions formed from elements.
• Be able to classify elements as metals or nonmetals.
• Review the naming of monatomic ions.
• Recall that metals form cations, and nonmetals form anions. Know the names and charges of elemental cations and anions.
• You'll have to be able to work with conversion factors be able to connect compound formulas with element composition.
• Review significant figures.

• Molecular compounds are made of molecules.
  • each molecule contains anywhere from two atoms (diatomic molecules) to thousands (biological molecules).
  • each molecule has the same element composition and properties as the compound.
  • synonym: covalent compound

• A molecular formula shows the type and number of atoms in a molecule
• type of atom indicated by element symbol
• number of atoms per molecule indicated by subscripts (if greater than one)
  • H₂O contains 2 hydrogen atoms and one oxygen atom per molecule.
  • Carbon tetrafluoride, CF₄, contains four fluorine atoms and one carbon atom per molecule.
• atoms in formulas are sometimes grouped to show how they're connected in the molecule
  • Methanol is usually written as CH₃OH to show that 3 hydrogens are bound to the carbon and another hydrogen is bound to the oxygen.
  • Acetic acid can be written as CH₃COOH or as HC₂H₃O₂ or C₂H₄O₂. The first formula shows how the molecule is put together; the second formula emphasizes that one hydrogen is different from the others; the third formula is the least informative because it shows only the numbers and types of atoms in the molecule.
• groups that appear more than once in the molecule are enclosed in parentheses
  • CH₃(CH₂)₃CH₃ could be written as C₅H₁₂, but all information about the structure of the molecule would be lost.
  • (CH₃CH₂)₄P₂O₇ molecules contain 8 carbons, 20 hydrogens, two phosphoruses, and seven oxygens.
• molecular weight = sum of weights of atoms in the molecule
  • The molecular weight of CH₃OH is approximately 12 + 4*1 + 16 = 32 since the carbon, hydrogen, and oxygen have atomic weights of 12, 1, and 16 u, respectively.

Formulas for ionic compounds

• empirical formula gives the elemental composition of a compound
  • formula lists elements present by element symbol
  • subscripts give ratios of ions or atoms in the compound
    

    CuSO₄ contains 4 atoms of O and 1 atom of S for every 1 atom of Cu.
    Na₂CO₃ contains 2 atoms of Na and 3 atoms of O for every 1 atom of C.

• writing ionic empirical formulas
  1. write the cation formulas, including charge
  2. write the anion formulas, including charge
  3. combine enough cations with enough anions to give a total charge of zero
     • trick: swap charges as subscripts
     • don't write charges when the ions are combined
  4. use the simplest (lowest) cation-to-anion ratio possible
  5. list cations first, anions last

  Potassium ions (K⁺) and chloride ions (Cl^-) combine to give potassium chloride, KCl
  Calcium ions (Ca²⁺) and bromide ions (Br^-) combine to give calcium bromide, CaBr₂
  Aluminum ions (Al³⁺) and sulfide ions (S^2-) combine to give aluminum sulfide, Al₂S₃
  

• naming ionic compounds from formulas
  1. name the anions
  2. name the cations
     • recall that the names of transition metal and main group cations must include their charge as a Roman numeral.
  3. the name of compound is cation name followed by anion name

  Na₂S contains sodium ion and sulfide ion. The compound is sodium sulfide. SnCl₄ contains a tin cation and four chloride ions. Each chloride carries a -1 charge, so the tin must have a +4 charge. The compound is tin(IV) chloride.
  

• the formula weight is the sum of atomic weights for atoms in the formula

  Na O H

  NaOH: 23.0 u + 16.0 u + 1.0 u 40.0 u

  Na C O

  Na2CO3 2×23.0 u + 12.0 u + 3×16.0 u 106.0 u

  N H S O

  (NH4)2SO4 2× 14.0 u + 2×4×1.0 u + 32.0 u + 4×16.0 u 132.0 u

• definition: ions formed from more than one atom
• examples: ammonium (NH₄⁺), hydroxide (OH^-), nitrate (NO₃^-), sulfate (SO₄^-)
• polyatomic ions retain their identity within ionic compounds, and in many reactions

• definition: a map that shows how atoms are bonded within a molecule

  molecular formula	structural formula	molecular model
  H2O

• structural formulas of polyatomic ions are bracketed, with the charge indicated by a superscript

  NH4+

• Sticks indicate shared electron pairs. There can be more than one pair shared, as in the C=O group in this acetic acid molecule.

  HC2H3O2

• to obtain a molecular formula from an empirical formula:
  1. you must know the molecular weight
  2. compute the ratio of molecular weight to formula weight
  3. multiply all subscripts in the empirical formula by this ratio
• examples

  Give the molecular formula for a compound with empirical formula CH and molecular weight 78.11 daltons.

  Give the molecular formula for a compound with empirical formula CH₂O and molecular weight 180 daltons.

• release hydrogen ions when dissolved
• leading H's in formula are acidic hydrogens
• guidelines for naming acids
  1. name the anion within the acid
  2. change the anion ending to one of the following:

     anion ending	in acid, replace with:	examples
     *ide	hydro*ic acid	hydrochloric acid, HCl
     -ite	-ous acid	nitrous acid, HNO2
     -ate	-ic acid	sulfuric acid, H2SO4

Binary Covalent Compounds

• naming binary covalent compounds
  1. write the name of the first nonmetal
  2. write the name of the second nonmetal with the ending changed to -ide
  3. insert prefixes into the name to reflect subscripts in the formula:

mono-	1	hexa-	6
di-	2	hepta-	7
tri-	3	octa-	8
tetra-	4	nona-	9
penta-	5	deca-	10

4. never start a name with mono-
• examples

  N2S5	dinitrogen pentasulfide	NO2	nitrogen dioxide
  S2Cl2	disulfur dichloride	N2O4	dinitrogen tetroxide
  SF6	sulfur hexafluoride	N2O5	dinitrogen pentoxides

• common names should be used for the following compounds:

  formula	common name
  H2O	water
  H2O2	hydrogen peroxide
  H2S	hydrogen sulfide
  N2O	nitrous oxide
  NO	nitric oxide
  NH3	ammonia
  N2H4	hydrazine

Addition Compounds

• contain several compounds packed in regular way into a crystal
• formulas of addition compounds
  • added compounds are separated by a dot
  • prefix compound with the number of times it occurs per formula unit
• naming addition compounds
  • translate numbers after a dot into Greek prefixes
  • name each compound in order
  • cross out first redundant ion names
  • water in addition compounds is called hydrate
    • hydration waters can be driven off by strong heating
    • compound with all hydration waters driven off is called anhydrous
    • anhydrous salts usually absorb water from air to become hydrates again
• examples

  Formula	Name
  Na2SO4 · 10H2O	sodium sulfate decahydrate
  CuSO4 · 5H2O	copper(II) sulfate pentahydrate
  CaCO3 · MgCO3	calcium magnesium carbonate	carbonate is named only once
  CaHPO4 · 2H2O	calcium hydrogen phosphate dihydrate
  Ga2(SO4)3 · 18H2O	gallium(III) sulfate 18-hydrate	Use numbers instead of prefixes when the number is larger than 12
  ZnSO4 · (NH4)2SO4 ·6H2O	zinc ammonium sulfate hexahydrate	zinc is always +2, so zinc(II) is not necessary

Copyright © 1997-2005 by Fred Senese
Comments & questions to fsenese@frostburg.edu
Last Revised 12/14/21.URL: http://antoine.frostburg.edu/chem/senese/101/compounds/index.shtml