Humboldt State University ® Department of Chemistry

Richard A. Paselk

General Chemistry

Supplemental Study Modules

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Lewis Structures

Draw Lewis Structures of the compounds below. Recall that positively charged ions retain the element name in compounds, while negatively charged elemental ions are given the -ide ending. For covalent compounds the more positive (less electronegative) element is usually given the element name, while the more electronegative element is given the -ide ending.

In general we can predict how electrons distribute in compounds using the Hi-Lo-Intermediate electronegativity rules:

  1. Compounds composed of a "Hi" and a "Lo" element will be ionic with the respective ions combining to give a neutral compound.
  2. All other combinations will give covalent compounds following the "octet rule" whenever possible.

A Periodic Table is provided with Hi (red), Lo (gray) and Intermediate (green) Electronegativities indicated to aid in prediting ionic vs. covalent compounds.

Multiple Bonds

Recall we must show an octet (or duet for Period I) in the outer-most shell (valence electrons). When this does not occur with single electron pairs (bonds) between atoms can sometimes make it happen with multiple bonds. You might find "Clark's Method" useful for determining the bonding patterns of various molecules:

Periodic Table of the Elements
   IA IIA IIIA IVA VA VIA VIIA VIIIA
   H  He
2 Li Be    B C N O F Ne
3 Na Mg IIIB IVB VB VI VIIB VIIIB IB IIB  Al Si P S Cl Ar
4 K Ca Sc  Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
5  Rb Sr  Y Zr Nb Mo Tc Ru Rh Pd  Ag  Cd  In Sn Sb Te I  Xe
6  Cs Ba Lu  Hf Ta  W Re Os Ir  Pt Au  Hg Tl  Pb Bi Po At Rn
  1. Phosphide ion

  2. Bromide ion

  3. Rubidium fluoride

  4. Cesium nitride

  5. Methane, CH4

  6. Hydrogen sulfide

  7. Carbon monoxide

  8. Barium iodide

  9. Ammonia, NH3

Set A - Answers 1-9

Periodic Table of the Elements
   IA IIA IIIA IVA VA VIA VIIA VIIIA
   H  He
2 Li Be    B C N O F Ne
3 Na Mg IIIB IVB VB VI VIIB VIIIB IB IIB  Al Si P S Cl Ar
4 K Ca Sc  Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
5  Rb Sr  Y Zr Nb Mo Tc Ru Rh Pd  Ag  Cd  In Sn Sb Te I  Xe
6  Cs Ba Lu  Hf Ta  W Re Os Ir  Pt Au  Hg Tl  Pb Bi Po At Rn
  1. Formaldehyde, CH2O

  2. Strontium nitride

  3. Cyanide ion, CN-

  4. Carbon dioxide, CO2

  5. Chloromethane, CH3Cl

  6. Acetic acid, CH3CO2H

  7. Ozone, O3

  8. Sulfite ion

  9. Water, H2O

  10. Carbocation, CH3+

Set B - Answers 1-10


In addition to these exercises you should familiarize yourself with the materials in your text and lab manual.


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© R A Paselk

Last modified 10 April 2013