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Science Dept.

Chemistry CHE 100 Notes
F. The Structure of Compounds

1. Valence and Oxidation State
   1. Valence Definition: A whole number used to describe the combining capacity of an element in a compound

   2. Oxidation State Definition: A whole number used to describe the combining capacity of an element in a compound with a + or a - assigned

   3. For Example, in combination with H⁺
      1. in HCl,....... the valence of Cl is _____
      2. in H₂O,...... the valence of O is _____
      3. in H₂SO₄,.. the valence of the sulfate radical _____
      4. in MgCl₂,.. the valence of Mg is _____
      5. in AlCl₃,.... the valence of Al is _____
      6. in CO,........the valence of C is _____
      7. in CO₂,..... the valence of C is _____

   4. Ions
      1. Cations: + ions, attracted to the negative cathode

      2. Anions: - ions, attracted to the positive anode

   5. Rules for Oxidation Numbers
      1. For compounds, the sum of the Oxidation Numbers = 0
      2. The free or uncombined element = 0
      3. If dealing with an ion, the Oxidation Number = ionic charge
      4. The negative Oxidation Number is assigned to the more electronegative element
      5. H is almost always +1 (except in NaH where H is -1)
      6. O is almost always -2 (except in peroxides where O is -1)
      7. In halides, the Oxidation Number is -1, eg. in NaCl Cl is -1
      8. In all sulfides, S is -2, eg. in H₂S

2. Chemical Bonds
   1. Types of bonds
      1. Ionic: electrostatic force of attraction between + and - ions

      2. Covalent: sharing of electrons, including equal, polar and coordinate

      3. Van der Waals

      4. Metallic

   2. Noble Gases: have a stable outer electronic level
      1. He: 1S²

      2. Ne: 1S² 2S² 2P⁶

      3. Ar: 1S² 2S² 2P⁶ 3S² 3P⁶

3. Ionic Bonds
   1. Na --> Na⁺ + 1e^- ..... a loss of an electron
   2. the ATOM:.... ₁₁Na 1S² 2S² 2P⁶ 3S¹
   3. the ION:........ ₁₁Na⁺ 1S² 2S² 2P⁶

   4. Cl + 1e^- --> Cl^- ..... a gain of an electron
   5. the ATOM:.... ₁₇Cl 1S² 2S² 2P⁶ 3S² 3P⁵
   6. the ION:........ ₁₇Cl^- 1S² 2S² 2P⁶ 3S² 3P⁶

   7. The Formation of Ionic Compounds
      1. Transfer of electrons results in changes in properties
      2. Charge of ion related to the # of protons and # of electrons
      3. The radius of an ion differ from the radius of its atom
      4. Energy is given off in bond formation
      5. No molecules, but formula units representing the simplest formula

4. Covalent Bonds: sharing of electrons
   1. Molecules and Radicals

   2. Electronegativity: the tendency of an atom to attract a pair of electrons (shared with a different atom) in a covalent bond

   3. The Case of Equal Sharing, the H₂ molecule
      1. The H₂ molecule can be written as:
         1. The Chemical Formula: H₂
         2. The Structural Formula: H-H, where the - stands for two shared electrons, one electron from one atom, the other electron from the other atom
         3. The Electron Dot Formula: H    H     (you complete)

   4. The Case of Unequal Sharing, Polar Molecules
      1. The HCl molecule can be written as:
         1. The Chemical Formula: HCl
         2. The Structural Formula: H-Cl, where the - stands for two shared electrons, one electron from one atom, the other electron from the other atom
         3. The Electron Dot Formula: H    Cl     (you complete)

   5. The Coordinate Covalent Case
      1. Definition: A Covalent Bond where both of the electron come from the same atom

      2. Ammonia Gas, an Example of Regular Covalent Bonds
         1. The Chemical Formula for Ammonia Gas: NH₃

         2. Give the Structural Formula for NH₃

         3. Give the Electron Dot Formula for: NH₃

      3. The Ammonium Radical, an Example of a Coordinate Covalent Bond
         1. The Chemical Formula for the Ammonium Radical: NH₄⁺

         2. Give the Structural Formula for NH₄⁺

         3. Give the Electron Dot Formula for: NH₄⁺

5. Electron Dot Formulas
   1. Give the Lewis Structure for the following:
      1. Water, H₂O :

      2. Methane, CH₄ :

      3. Carbon Dioxide, CO₂ :

      4. Hydrogen Cyanide, HCN :

6. Polyatonic Ions = Radicals
   1. Learn the Following Radicals
      1. Ammonium Radical: NH₄⁺

      2. Carbonate Radical: CO₃^2-

      3. Bicarbonate (Hydrogen Carbonate) Radical: HCO₃^-

      4. Sulfate Radical: SO₄^2-

      5. Sulfite Radical: SO₃^2-

      6. Bisulfate (Hydrogen Sulfate) Radical: HSO₄^-

      7. Bisulfite (Hydrogen Sulfite) Radical: HSO₃^-

      8. Nitrate Radical: NO₃^-

      9. Nitrite Radical: NO₂^-

7. Writing Formulas: Write the Formula for the Following Compounds
   1. Sodium Chloride

   2. Potassium Bromide

   3. Calcium Chloride

   4. Lithium Sulfate

   5. Magnesium Chloride

   6. Magnesium Carbonate

   7. Magnesium Bicarbonate

8. How About a Quick Quiz?