ppt14 b - ucsbdevries/chem1c/handouts/ppt14 b.pdf · title: microsoft powerpoint - ppt14 b...

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Covalent Bonding:

b

Covalent Bonding: Orbitals

Figure 13.1: (a) The interaction of two hydrogen atoms (b) Energy profile as a function of the distance

between the nuclei of the hydrogen atoms.

Copyright © Houghton Mifflin Company. All rights reserved. 14a–2

Figure 13.1: (a) The interaction of two hydrogen atoms (b) Energy profile as a function of the distance

between the nuclei of the hydrogen atoms.


Figure 14.25: The combination of hydrogen 1s atomic orbitals to form MOs


Copyright © Houghton Mifflin Company. All rights reserved. 14a–510.6

- (- sign flips phase of the sound wave function)

- = 0


Auto mufflers use destructive interferenceof sound waves to reduce engine noises.

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Bose is $200. Want todo it yourself?See Web site.

http://www.headwize.com/projects/noise_prj.htmCopyright © Houghton Mifflin Company. All rights reserved. 14a–8

An analogy between light waves and atomic wave functions.

NOTE: +/- signs show PHASES of waves, NOTCHARGES!


Amplitudes of wave functions added

Amplitudes of wave functions subtracted.

Figure 14.26: (a) The MO energy-level diagram for the H2 molecule (b) The shapes of the Mos are obtained

by squaring the wave functions for MO1 and MO2.


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Figure 14.27: Bonding and anitbonding MOs


Figure 14.28: MO energy-level diagram for the H2 molecule

# ANTIBONDING e’s = 0


# BONDING e’s = 2

# ANTIBONDING e s = 0

Bond order = ½(2-0) = 1

Figure 14.29: The MO energy-level diagram for the He2 molecule



# BONDING e’s = 2

Bond order = ½(2-2) = 0

Figure 14.29: The MO energy-level diagram for the He2 molecule


Figure 14.30: The MO energy-level diagram for the He2

+ ion.



# BONDING e’s = 2

Bond order = ½(2-1) = ½

Figure 14.31: The MO energy-level diagram for the H2

+ ion


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Figure 14.32: The MO energy-level diagram for the H2

- ion

Copyright © Houghton Mifflin Company. All rights reserved. 14a–19 Copyright © Houghton Mifflin Company. All rights reserved. 14a–20

Figure 14.33: The relative sizes of the lithium 1s and 2s atomic orbitals


Figure 14.34: The MO energy-level diagram for the Li2 molecule


Figure 14.35: The three mutually perpendicular 2p orbitals on tow adjacent boron atoms.


Figure 14.37: The expected MO energy-level diagram for the combustion of the 2P orbitals

on two boron atoms.


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Figure 14.36: The two p oribitals on the boron atom that overlap head-on combine to form

bonding and antibonding orbitals.


Figure 14.36: The two p oribitals on the boron atom that overlap head-on combine to form

bonding and antibonding orbitals.



on two boron atoms.



on two boron atoms.



on two boron atoms.


Figure 14.38: The expected MO energy-level diagram for the B2 molecule


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Figure 14.39: An apparatus used to measure the paramagnetism of a sample


Figure 14.40: The correct MO energy-level diagram for the B2 molecule.


Figure 14.41: The MO energy-level diagrams, bond orders, bond energies, and bond lengths for the

diatomic molecules, B2 through F2.


Figure 14.42: When liquid oxygen is poured into the space between the poles of a strong magnet, it remains

there until it boils away.


Source: Donald Clegg

Figure 14.43: The MO energy-level diagram for the NO molecule


Figure 14.44: The MO energy-level diagram for both the NO+ and CN- ions


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Figure 14.45: A partial MO energy-level diagram for the HF molecule


Figure 14.46: The electron probability distribution in the bonding MO of the HF molecule


Spectroscopy


Electromagnetic spectrum


(wavelength) x (frequency) = speed [m/s]E = h ν

EnergyPer photon:

λν = c [108 m/s]


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Electromagnetic spectrum


λν

WHAT MAKES A MOLECULE ABSORB LIGHT?

When should you push?


AT THE RESONANTFREQUENCY

λν=cAT THE RESONANTFREQUENCY

14* Electronic transitions: ~ 6 x 10 sec.

500 nm (UV-VIS)


Figure 14.55: The molecular orbital diagram for the ground state of NO+


λν=cAT THE RESONANTFREQUENCY

14* Electronic transitions: ~ 6 x 10 sec.

500 nm (UV-VIS)


13* Nuclear vibration: ~ 3 x 10 sec.

10,000 nm (

* molecular rotation:

mi

IR)

crowaves


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What makes a molecule absorb light?

[cm-1] = 1/λ = ν/c =E/hc

Figure 14.60: The three fundamental vibrations for sulfur dioxide



What makes a molecule absorb light?

3200 cm−1 broad, strong O-H stretch (alcohols)3000 cm−1 broad, medium O-H stretch (carboxylic acids)1200 cm−1 strong, O-H bending2800 cm−1 strong, C-H stretch 1400 cm−1 variable C H bending1400 cm 1 variable, C-H bending1700 cm−1 strong, C=O stretch 1200 cm−1 strong, C-O stretch

What makes a molecule absorb light? Figure 14.61: The infrared spectrum of CH2Cl2.


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What makes a molecule absorb light? Figure 14.52: Schematic representation of two electronic energy levels in a molecule


Figure 14.53: The various types of transitions are shown by vertical arrows.


Figure 14.54: Spectrum corresponding to the changes indicated in Fig. 14.53.


The molecular structure of beta-carotene


Figure 14.57: The electronic absorption spectrum of beta-carotene.


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VIBRATIONS VIBRATIONS

Figure 14.58: The potential curve for a diatomic molecule


Figure 14.59: Morse energy curve for a diatomic molecule.


Figure 14.62: Representations of the two spin states of the proton interacting


Figure 14.63: The molecular structure of bromoethane


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Figure 14.64: The expected NMR spectrum for bromoethane


Figure 14.65: The spin of proton Hy

can by "up" or "down"


Figure 14.66: The spins for protons Hy

can be "up", can be opposed (in 2


ways) or can both be "down"

Figure 14.67: The spins for the protons Hy can by arranged as shown in (a) leading to four different


magnetic environments

Figure 14.68: The NMR spectrum of CH3CH2Br (bromoethane) with TMS reference


Figure 14.69: The molecule (2-butanone)


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Figure 14.70: A technician speaks to a patient before heis moved intot eh cavity of a magnetic

resonance imaging (MRI) machine.


Figure 14.71: A colored Magnetic Resonance Imaging (MRI) scan through a human head,

showing a healthy brain in side view.


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