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RULES FOR DRAWING LEWIS STRUCTURES : All Species with Covalent Bonds
- 1. Sum the valence electrons from all atoms.
- If the species is an ion, add an electron for each negative charge and subtract an electron for each positive charge.
- 2. Place atoms on paper.
- Write the symbols for the atoms involved so as to show which elements are attached to which. Atoms are often written in the order in which they are connected in the molecule or ion, as in HCN. When a central atom has a group of other atoms bonded to it, we usually write the central atom first, as in CH4. It is very unusual for two atoms of the same element to bond together in a compound. The major exception to this rule is carbon, which forms millions of compounds in which carbon atoms are bonded to each other.
- 3. Place valence electrons around the atoms so that the Rule of Eight (see table below) is obeyed and all available valence electrons are used in the Lewis Dot Structure.
- First try, assume that there is one shaired pair of electrons (called bonding pairs) are placed between each pair of elements. A bond that has one shared or bonded pair is a called a single bond; 2 = double bond , 3 = triple bond.
Rule of Eight or Octet Rule
- Add up all the valence electrons in the Lewis Dot Structure:
- If number = available valence electrons, correct Lewis Dot Structure.
- If number is greater than available valence electrons, need to share more electrons, so try multiple bonds (i.e. a double bond). Most multiple bonds are made between atoms of carbon, nitrogen, oxygen sulfur, phosphorous and a few other elements.
- If number is less than available valence electrons, place any leftover electrons on the central atom.
All atoms need 8 valence electron around it after finishing bonding (correct Lewis Dot Structure).
a. H - 2 valence e-
b. Be - 4 valence e-
c. B - 6 valence e-
d. 3rd row or greater elements (called Exceeding Octet Rule)
DRAW LEWIS DOT STRUCTURES FOR EACH OF THE FOLLOWING COMPOUNDS.
5. Be F2
10. Cl O31-
[Good website for Lewis Dot Structures Notes (Ionic cpds & Molecules)]
[Better Direction for Drawing Lewis Dot Structure - Lecture Notes]
[Good site for VSPER including Shapes & Examples]