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The purpose of this week's assignment is to practice drawing Lewis dot structures.

Acetic acid, CH₃COOH, is the component of vinegar that gives it its odor and taste. In order to draw the Lewis structure of acetic acid, you need to determine the number of valence electrons. Carbon has 4, oxygen has 6, and hydrogen has 1 valence electron. So, two carbon atoms times 4 electrons, plus two oxygen atoms times 6 electrons, plus four hydrogen atoms times 1 valence electron equals 24 valence electrons. 2(4)+2(6)+4(1)=24 valence electrons.

	Look at the Lewis structure of acetic acid. Do you see 24 valence electrons? Remember each dash represents two electrons and each lone pair is two electrons. There are 6 single bonds and one double bond in this structure and two lone pairs of electrons on each oxygen.
acetic acid

	1. Determine the number of valence electrons for NH2CHCHOH by looking only at the formula. 2. Look at the structure on the left. Do all of the atoms have an octet (or a duet in the case of hydrogen)? If not, you need to add lone pairs to satisfy each atom. Explain where you would put lone pairs.
NH2CHCHOH

Chloroform, CHCl₃, was an early anesthetic. Let's draw a Lewis structure for chloroform. First, determine the number of valence electrons. The next step is to write carbon as the central atom. Now, place hydrogen and chlorine atoms around the carbon. Draw a bond between carbon and each surrounding atom. Place lone pairs of electrons around any atom still needing an octet. (Remember, 2 electrons are all hydrogen needs to be satisfied.)

Examine your initial attempt to draw the Lewis structure of chloroform. Does every atom have an octet? Does the total number of electrons in your Lewis structure match the number of valence electrons actually available? If yes, cool. If not, do what all chemists do and rework your structure. Remember, drawing Lewis structures correctly involves a trial and error process.