CHEM 1127Q Lecture Notes - Lecture 18: Octet Rule, Sigma Bond, Unpaired Electron

Lewis structures of some molecules with multiple bonds Multiple bonds are represented with more than one straight line between atoms. A double bond is formed when two atoms share two pairs of electrons and is stronger than a single bond. A triple bond s formed when two atoms share three pairs of electrons and is stronger than a double bond. What is the total number of electrons shown in the Lewis structure in Model 5 for each molecule? Compare your answers to CTQs 19 and 21. How does one determine the total number of electrons that should be used to generate a Lewis structure? For N_2, is the sum of the bonding electrons and the lone pair electrons around each N atom consistent with the Lewis model? In other words, does each N have an octet? Write a sentence to explain. For H_2CO: a. Is the sum of the bonding electrons and the lone pair electrons around each C atom consistent with a complete octet? b. Is the sum of the bonding electrons and the lone pair electrons around each 0 atom consistent with a complete octet? Using the information from above, construct a checklist that can be used to determine if a Lewis structure for a molecule is correct. Try to think of at least three criteria. Compare your criteria with your team and try to come to agreement. List any questions that remain with your team about Lewis dot structures.

First you need to find the number of valence electrons in NH_2Cl_2. For counting purposes with Lewis structures, the number of valence electrons in an atom of a main group element is equal to the last digit in the group number of that element in the Periodic Table. N is in Group __________ H is in Group _______________ Cl is in Group _____________ In NH_2Cl there is a total of ____________ valence electrons. The model consists of balls and sticks. How many holes should be in the ball you select for the N atom? __________ the H atoms? _____________ the Cl atom? ___________ The electrons in the molecule are paired, and each stick represents a valence electron pair. How many sticks do you need? ______________ Assemble a skeleton structure for the molecule, connecting the balls and sticks to make one unit. Use the rule that N atoms form three bonds, whereas Cl and H atoms usually form only one. Draw a sketch of the skeleton below: How many sticks did you need to make the skeleton structure? __________ How many sticks are left over? ____________ If your model is to be obey the octet rule, each ball must have four sticks in it (except for hydrogen atom balls, which need and can only have one). (Each atom in an octet rule species is surrounded by four pairs of electrons.) How many holes remain to be filled? _____________ Fill them with the remaining sticks, which represent nonbonding electron pairs. Draw the complete Lewis structure for NH_2Cl using lines for bonds and pairs of dots for nonbonding electrons. Describe the geometry of the model, which is that of NH_2Cl. __________ Is the NH_2Cl molecule polar? ___________ Why? Would you expect NH_2Cl to have any isomeric forms? _____________ Explain your reasoning. Would NH_2Cl have any resonance structures? __________ If so, draw them below.