Question 1. Electron Configurations Noble Gases and The Rule of Eight. Chapter 1. What is the electronic configuration of carbon?

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1 hapter ~. nm Electronic Structure and Bonding Anders Jöns Ångström (84-874) Å = picometers =. nanometers = -4 microns = -8 centimeters Acids and Bases nm = Å An atom vs. a nucleus ~, x larger ucleus = /, of the atom Question What is the electronic configuration of carbon? A) s 2 2s 2 2p 2 x B) s 2 2s 2 2p x 2p y 2p z ) s 2 2s 2 2p x 2p y 2p z D) s 2 p x p y 2s 2 Electron onfigurations oble Gases and The Rule of Eight When two nonmetals react to form a covalent bond: They share electrons to achieve a oble gas electron configuration. When a nonmetal and a metal react to form an ionic compound: Valence electrons of the metal are lost and the nonmetal gains these electrons. G.. Lewis Photo Bancroft Library, University of alifornia/lbl Image Library Footnote: G.. Lewis, despite his insight and contributions to chemistry, was never awarded the obel prize. otes from Lewisʼs s notebook and his Lewis structure.

2 Ionic ompounds Ionic compounds are formed when electron(s) are transferred. Electrons go from less electronegative element to the more electronegative forming ionic bonds. ovalent ompounds Share electrons. pair = bond. ctet rule ( duet for hydrogen) Lewis structures: otice the charges: In one case they balance, can you name the compound? In the other they do not, can you name the polyatomic ion? More about formal charge to come. Question 2 Important Bond umbers (eutral Atoms / ormal electron distribution) Select the correct Lewis structure for methyl fluoride ( 3 F). one bond two bonds F l Br I ) D) three bonds four bonds Question 3 Question 4 What is the correct Lewis structure of formaldehyde ( 2 )? ) D) Which of the following contains a triple bond? A) S 2 B) ) 2 4 D) 3

3 Important Bond umbers (eutral Atoms / ormal electron distribution) one bond F l Br I Formal harge Formal charge is the charge of an atom in a Lewis structure which has a different than normal distribution of electrons. two bonds three bonds four bonds Important Bond umbers (eutral Atoms / ormal electron distribution) rganic hemistry # of Valence e - s Formal harge Formal charge = number of valence electrons (number of lone pair electrons /2 number of bonding electrons) Total # of Bonds (neutral atom) ombinations of bonds (neutral atom): # of single bonds # of double bonds # of triple bonds Total Bonds Equals the number of valence electrons (Group umber of the free atom) minus [the number of unshared valence electrons in the molecule /2 the number of shared valence electrons in the molecule]. Moving/Adding/Subtracting atoms and electrons. # of Free Pairs of electrons 2 2 omplete the following table. It summarizes the formal charge on a ( central ) atom for the most important species in organic chemistry. 3 itric Acid

4 Question 5 What is the formal charge of the carbon atom in the Lewis structure? A) - B) ) D) 2 Question 6 What is the formal charge of the oxygen atom in the Lewis structure? A) - B) ) D) 2 Resonance Resonance is a very important intellectual concept that was introduced by Linus Pauling in 928 to explain experimental observations. Resonance Eg. S 2 Bond order.5 Bond length > double bond; < single bond TUTRIAL Resonance Two or more Lewis structures may be legitimately written for certain compounds (or ions) that have double bonds and/or free pairs of non-bonded electrons It is a mental exercise in pushing or moving electrons. Refer to Table.6 Rules of Resonance Step : The atoms must stay in the same position. Atom connectivity is the same in all resonance structures. nly electrons move. -Example: The Lewis formulas below are not resonance forms. A hydrogen atom has changed position.

5 Rules of Resonance Step 2: Each contributing structure must have the same total number of electrons and the same net charge. Example: All structures have 8 electrons and a net charge of. Rules of Resonance Step 3: alculate formal charges for each atom in each structure. Example: one of the atoms possess a formal charge in this Lewis structure. Rules of Resonance Step 4: alculate formal charges for the second and third structures. Example: These structures have formal charges. TE: They are less favorable Lewis structures. Pushing Electrons same atomic positions differ in electron positions : : more stable less stable Lewis Lewis structure structure Pushing Electrons Why use Resonance Structures? same atomic positions differ in electron positions only : : more stable less stable Lewis Lewis structure structure Delocalization of electrons and charges between two or more atoms helps explain energetic stability and chemical reactivity. Electrons in a single Lewis structure are insufficient to show electron delocalization. A composite of all resonance forms more accurately depicts electron distribution. (YBRID) TE: Resonance forms are not always evenly weighted. Some forms are better than others.

6 Resonance Example Resonance Example zone ( 3 ) zone ( 3 ) Lewis structure of ozone shows one double bond and one single bond Lewis structure of ozone shows one double bond and one single bond Expect: one short bond and one long bond Reality: bonds are of equal length (28 pm) Resonance: zone ( 3 ) Resonance Example Detailed Resonance Examples Electrostatic potential map shows both end carbons are equivalent with respect to negative charge. Middle carbon is positive. Question 7 Which resonance structure contributes more to the hybrid? VSEPR Model Valence Shell Electron Pair Repulsion

7 VSEPR Model The molecular structure of a given atom is determined principally by minimizing electron pair (bonded &free) repulsions through maximizing separations. Some examples of minimizing interactions. Predicting a VSEPR Structure. Draw Lewis structure. 2. Put pairs as far apart as possible. 3. Determine positions of atoms from the way electron pairs are shared. 4. Determine the name of molecular structure from positions of the atoms. rbital Molecular Geometry Geometry Bond Angle # of lone pairs Lewis Structures / VSEPR / hem 226 Linear Linear Trigonal Planar Trigonal Planar Tetrahedral Tetrahedral Trigonal Planar Bent Tetrahedral Trigonal Pyramidal Molecular Models omputer Generated Models Tetrahedral Bent 2 ctahedral Seesaw T-shape Linear ctahedral 2 3 Ball and stick models of ammonia, water and methane. ctahedral ctahedral Square Pyramidal Square Planar 2 Worksheet : Bonds, Formulas, Structures & Shapes ovalent ompounds Equal sharing of electrons: nonpolar covalent bond, same electronegativity (e.g., 2 ) Unequal sharing of electrons between atoms of different electronegativities: polar covalent bond (e.g., F)

8 Question 8 Which of the following bonds is the most polar? ) D) Bond Dipole & Dipole Moment Question 9 Dipole moments are experimentally measured. Polar bonds have dipole moments. dipole moment (D) = µ = e x d (e) : magnitude of the charge on the atom (d) : distance between the two charges Which of the following bonds have the greatest dipole moment (µ)? ) D) Bond Polarity A molecule, such as F, that has a center of positive charge and a center of negative charge is polar, and has a dipole moment. The partial charge is represented by δ and the polarity with a vector arrow. F!!" Question In which of the compounds below is the δ for the greatest? A) 4 B) 3 ) Si 4 D) 2

9 Question In which of the following is oxygen the positive end of the bond dipole? A) -F B) - ) -S D) -