7/15/2015 One Point Quiz  One quiz per table, list everyone’s name  Agree on an answer  You have two minutes

Exam 3 Results Nomenclature Average = 95/110

Hardest Questions?  Why is the first ionization energy of nitrogen greater than carbon, oxygen or phosphorous? Li Be B C N O F Ne kcal Primary reason: Change of nuclear charge. Secondary reason: Electronic configuration effects.

Hardest Questions?  Why is the melting point of magnesium oxide 2000 degrees greater than potassium bromide? (two factors) Ionic bonding lattice energy  q 1 x q 2 / r

Orbital Hybridization Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

7/15/2015 Bonding Theories  Ionic Model  Skeleton Diagrams  Lewis Dot Diagrams  Molecular Orbital Theory  Orbital Hybridization Extends molecular orbitals concepts to atoms

7/15/2015 Beryllium Hydride Be: 1s 2 2s 2 2p 0 H: 1s 1 Be H H Impossible to fulfill the octet of beryllium because there are only four valence electrons available. Draw a Lewis Dot structure for BeH 2

7/15/2015 Beryllium Hydride Be H  2z b  2s b H Using molecular orbital bonding theory the p-orbitals of beryllium must be used. This would indicate that each hydrogen is bound to beryllium by a different type of bond. Experimentally, the two Be-H bonds are identical same length, same bond energy (strength)

7/15/2015 Beryllium Hydride Be H  2z b  2s b Be H It is unlikely that  2s b and  2z b would be exactly equivalent. And, there’s another problem...

7/15/2015  2s b ) 3  2z b ) 1 Beryllium Hydride Open orbital contains no electrons Lined orbital contains one electron Filled in orbital contains two electrons What’s a solution? H Be H H  2z b ) 2 H Be  2s b ) 2 One overlap has one electron One overlap has three electrons hybridization Each overlap has two electrons

7/15/2015 Hybridization  The 2s and the 2p orbitals of beryllium have become equivalent to each other by merging or blending or "hybridizing".  These two new orbitals are called sp hybrid atomic orbitals (hao) Arises from one s orbital and one p orbital.

7/15/2015 Beryllium sp Hybridization Be and Two orbitals each can hold two electrons

7/15/2015 sp Hybridization Be p x, p y sp energy 2s 2p ao hao Maximum angle that two orbitals can be apart is 180°.

7/15/2015 sp Orbital Hybridization Be The shape is determined by the linear combinations of atomic orbitals  2s +  2p z and  2s -  2p z

7/15/2015 z y x sp Hybridized Beryllium Valence Orbitals Open orbital contains no electrons Lined orbital contains one electron Filled in orbital contains two electrons The other p-orbitals of beryllium (p x, p y ) remain unchanged HH Be z y x H two sigma bonds BeHH Why is it a linear molecule? H

7/15/2015 Ethene C H H C H H  Also called ethylene  Polymerizes to form polyethylene  Each carbon forms three sp 2 hybrid orbitals.

7/15/2015 One Point Quiz  One quiz per table, list everyone’s name  Agree on an answer  You have two minutes

7/15/2015 C + sp 2 Orbital Hybridization C 2s C+ = 2p z 2p x sp 2 The 2s, 2p x and 2p z atomic orbitals of each carbon are used. The angle between the orbitals is 120°.

7/15/2015 energy 2s 2p ao sp 2 Hybridization hao sp 2 The unhybridized p y orbital is perpendicular to the sp 2 orbitals. 2p y This hybrid set can hold six electrons.

7/15/2015 Ethene Top down view (xz plane) Edge on view y To allow for overlap of the unhybridized p y orbitals, the bonding in this molecule requires that ethene is planar. All six atoms lie in the same plane.

7/15/2015 Ethene C C HH HH carbon-carbon sigma bond due to sp 2 -sp 2 overlap carbon-carbon pi bond due to 2p y - 2p y overlap carbon-hydrogen sigma bonds due to sp 2 -s overlap

7/15/2015 Predicting Hybridization The number of hybrid orbitals an atom forms equals the number of unique directions that the electron pairs point, as determined by the Lewis Dot structure.

7/15/2015 Methane C HH H H The 2s, 2p x, 2p y and 2p z atomic orbitals of carbon are used. What would be the name of a hybrid orbital made from these orbitals?

7/15/2015 sp 3 Orbital Hybridization + 2s + 2p z 2p x + z y x 2p y

7/15/2015 sp 3 Orbital Hybridization four sp 3 orbitals The angle between the orbitals is 109.5°. Why isn’t the angle 90°? tetrahedral shape

7/15/2015 sp 3 Hybridization sp 3 energy 2s 2p carbon ao hao All four hybrid atomic orbitals have the same energy. These four orbitals are energetically degenerate.

7/15/2015 Methane H C H H H carbon-hydrogen sigma bonds due to sp 3 -s overlap

7/15/2015 Ammonia N HH H The 2s, 2p x, 2p y and 2p z atomic orbitals of nitrogen are used

7/15/2015 sp 3 Hybridization sp 3 nitrogen ao hao energy 2s 2p By hybridizing its atomic orbitals nitrogen gains more stable (lower energy) orbitals for bonding. Which of the electrons in these hybrid atomic orbitals are available for bonding?

7/15/2015 Ammonia H N H H a completely filled in orbital contains two electrons nitrogen-hydrogen sigma bonds due to sp 3 -s overlap Because of this bonding, the  H-N-H bond angle is close to 109.5° (actually 107°).

7/15/2015 The Structure of Ammonia What bond angle would be expected if the lone pair of electrons didn't affect the structure? What bond angle would be expected if the atomic orbitals of nitrogen did not hybridize? Why is the actual bond angle not exactly 109.5°? Draw the orbital overlap diagram for the reaction of ammonia and a hydrogen ion.

Groups of Electrons Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

Groups of Electrons H H N CO H Predicts bond angles hybridization of non-metal atoms in a molecule or ion Requires properly drawn Lewis Dot diagram

7/15/2015 Procedure  Draw the proper Lewis Dot diagram.  Determine the number of "groups of electrons" (“effective electron pairs”) around the central atom. All electrons pointing in the same direction are considered one group.  If only s and p orbitals are involved then the correct hybridization and ideal bond angle is predicted by the number of groups.

7/15/2015 One Point Quiz  One quiz per table, list everyone’s name  Agree on an answer  You have two minutes

7/15/2015 Groups of Electrons Hybridization Ideal Bond Angle 2sp180º 3sp 2 120º 4sp º

Groups of Electrons Formamide H H N CO H bond angle hybridization

7/15/2015 Hydrogen Cyanide C HN CNH 2 groups of electrons around carbon sp hybridization  H-C-N = 180° What does the orbital overlap diagram look like?

7/15/2015 Hydrogen Cyanide CNH carbon sp hybridized How many electrons are in each orbital? nitrogen sp hybridized How many electrons are in each orbital? hydrogen 1s orbital

7/15/2015 Hydrogen Cyanide CNH sigma bonds p x orbital overlap p y orbital overlap

7/15/2015 Hydrogen Cyanide sigma bonds (between hydrogen and carbon and carbon and nitrogen) 2 pi bonds CNH (between carbon and nitrogen)

7/15/2015 Nitrite Ion N O O N OO 3 groups of electrons around nitrogen sp 2 hybridization  120° Why is the bond angle approximately 120°? Draw the hybridized atomic orbitals for each atom O1 sp 2 hybridized O2 sp 3 hybridized

Nitrite Ion N O O 1s 2 2s 2 2p 4 1s 2 2s 2 2p 3 1s 2 2s 2 2p 4 _ _ _ _ _ sp 2 p1s _ _ _ _ _ sp 2 p1s _ _ _ _ _ sp 3 1s -1 charge

Nitrite Ion N O O What other kind of bond is formed?

7/15/2015 Nitrite Ion N O O Where is the pi bond located? O O N

7/15/2015 Nitrite Ion N OO How would the bonding change if O2 was unhybridized? N O O 3 groups of electrons around nitrogen sp 2 hybridization  120°

Nitrite Ion N O O 1s 2 2s 2 2p 4 _ _ _ _ _ sp 2 p1s 1s 2 2s 2 2p 3 _ _ _ _ _ sp 2 p1s -1 charge _ _ _ _ _ 2p1s2s

Nitrite Ion N O O What other kind of bond is formed?

7/15/2015 Nitrite Ion N O O pi bond formation How could resonance in this molecule be explained?

7/15/2015 Ethene H H C C H H C H H C H H 3 groups of electrons around carbon sp 2 hybridization  120°  120°

7/15/2015 Ethene C H H C H H How many sigma bonds and how many pi bonds are formed?

7/15/2015 Ethane C H H H C H H H C H H H C H H H 4 groups of electrons around carbon sp 3 hybridization  109.5°  109.5°

7/15/2015 Ethane C H H H C H H H What kind of bonds are formed?

Dipole Moments Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

7/15/2015 Dipole Moments  Charge is not always equally distributed in a molecule.  There can be a region of positive charge and of negative charge.  The vector connecting these regions is called the dipole moment.

7/15/2015 Dipole Moment HCl Chlorine is more electronegative than hydrogen. The dipole moment is drawn positive (+) to negative(-) (note: physics texts draw it the opposite way!)

7/15/2015 O H H Net Dipole Moment The (net) molecular dipole moment is the vector sum of the individual bond dipoles.

7/15/2015 FB F F BF F F Canceling Dipole Moments the net dipole moment of boron trifluoride is zero Sometimes a set of individual bond moments cancel each other.

7/15/2015 Boron Trifluoride FB F F What is the hybridization of boron in boron trifluoride? Can an alternate Lewis Dot diagram be drawn that obeys the octet rule?

7/15/2015 Boron Trifluoride B F F F B F F F B F F F What would be the hybridization and bond angles of the resonance structures? sp 2,  F-B-F = 120°

7/15/2015 H C H H H Canceling Dipole Moments the hydrogen atoms in methane are arranged in a tetrahedral shape the four vectors cancel each other The cancellation of individual bond moments can also occur in three dimensions.

7/15/2015 Carbon Monoxide CO negative formal charge more electronegative Which way does the dipole of carbon monoxide point? Electronegativity and formal charge both contribute to the dipole moment.

7/15/2015 Carbon Monoxide  The actual dipole is very small 0.11 D, and points in the direction of carbon! A debye is x C·m CO O H H The dipole moment of the water molecule is 1.87 D.

7/15/2015 Predictions  For molecular compounds solubility and miscibility are related to the polarity (i.e., dipole moment) of the molecule.  "Like dissolves like" is a rule of thumb for solubility polar molecules dissolve in polar solvents nonpolar molecules dissolve in nonpolar solvents

7/15/2015 Carbonate Ion O C O O 2- The concept of dipole moments can also be applied to ions, although they generally dissolve in polar solvents (e.g., water) because of their charge. Although carbonate ion has no net dipole moment, it dissolves in polar solvents because of its ionic charge.

7/15/2015 Like Dissolves Like  The rule "like dissolves like" is not perfect;  However, it does serve as a starting point in determining what type of solvent to use when attempting to dissolve a solid.

7/15/2015 Polarity Predictions  Rank the following molecules in terms of polarity: water, benzene, chloroform O H H Cl C H

7/15/2015 Polarity Predictions  [Cu(py) 2 (SCN) 2 ] dissolves in chloroform but not water. Rationalize this behavior.

7/15/2015 Electronegativity

7/15/2015

Exam 3 Results Nomenclature Average 89/110 ± 10

Hardest Question?  Rank the following in order of decreasing melting point: CaS, MgO, KCl Ionic bonding lattice energy  q 1 x q 2 / r 2