Organic Chem Ch. 2.pdf

4 Pages
Unlock Document

CHEM 261
Paul Lahti

Chapter 2 Polar Covalent Bonds Electronegativity The two bonding electrons are shared equally by the two equivalent carbon atoms resulting in a symmetrical electron distribution of the bond Most bonds are neither fully ionic nor fully covalent but are usually somewhere between those extremes Polar Covalent Bonds The bonding electrons are attracted more strongly by one atom that the other so that the electron distribution between atoms is not symmetrical Electronegativity EN The differences are what affect bond polarity also known as the intrinsic ability of an tom to attract the shared electrons in a covalent bond Bond polarity is expressed through a crossed arrow By convention this means that electrons are displaced in the direction of the arrow The tail of the arrow electron poorand the head of the arrow is electron richElectrostatic potential maps use color to indicate electron rich redand electron poor blueregions These maps are useful because they show at a glance the electronrich and electronpoor atoms in molecules Inductive Effect The shifting of electrons in a sigma bond in response to the electronegativity of nearby atoms Lithium and Magnesium both inductively donate electrons whereas reactive nonmetals such as oxygen and nitrogen inductively withdraw electrons 22 Polar Covalent Bonds Dipole Moments Dipole MomentGreek mu is defined as the magnitude of the charge Q at either end of the molecular dipole times the distance r between the charges Q x rEx Assume that there is a center of mass of all positive charges nuclei in a molecule and a center of mass of all negative charges electrons If these two centers dont coincide then the molecule has a net polarity Dipole moments are expressed in debyes D where 1 D3336 x 10 10 power coulomb meter Cm in SI units 23 Formal Charges Generally assigned to atoms that have an apparently abnormal number of bonds Formal charges are a formality and dont imply the presence of actual ionic charges in a molecule Instead they are a device for electron bookkeeping Can be thought of as Although the bonding electrons are shared by both atoms each atom can still be considered to own one electron for bookkeeping purposes Formal Charge Equal to the number of valence electrons in a neutral isolated atom minus the number of electrons owned by that bonded atom in a molecule The number of electrons in turn is equal to half the number of bonding electrons plus the nonbonding lonepair electrons 24 Resonance Resonance Forms The two individual linebond structures for an acetate ion and their resonance relationship is indicated by the double headed arrow between themThe only difference between resonance forms is the placements of the pi bonds and nonbonding valence electrons
More Less

Related notes for CHEM 261

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.