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CHEMISTRY 313

Tuesday, Thursday 10:30 – 11:45 a.m.

Enterprise Hall 178

Spring 2020

Prof. S. W. Slayden 333 Planetary Hall

sslayden@gmu.edu 703-993-1071

http://mason.gmu.edu/~sslayden Office Hours: 11:45 a.m.-12:30 p.m.

and other times by appointment

Please see the web syllabus at the URL, above, for updates.

Week of Text Chapter Klein Chapter Exam / Note

Jan. 20 1 Introduction

27 1, 2 1, 2

Feb. 3 2 2, 4 Add deadline 1/29

10 3; (11.2, 11.6) 3 Drop deadline 2/12

17 4; 2.4, 10.3, 10.3A,B, 10.5A,

7.15, 7.16A, 7.17A

5 Feb. 18

24 4 6

Mar. 2 4, 11.1

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9 SPRING BREAK

16 5; 3.1, 13.3, 13.4A

23 6 8.1-8.5 Mar. 24

30 6 9, 12.3

Apr. 6 7 10.7-10.9

13 7;8 10.1-10.6 Apr. 21

20 8; 11.4 11 (except 11.5,

11.10), 8.6-8.7

27 11 12.1, 12.2, 12.4,

12.8, 12.10

May 12, 10:30 a.m.

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Course Materials

Text "Organic Chemistry, 3rd Ed.", David Klein, Wiley, 2017

Wiley Plus The WileyPLUS package is made available by the publisher of the course textbook

by Klein. This electronic resource includes the full color digital text and many related learning

resources such as extensive practice problems, tutorials, videos and animations. See the CHEM

313 class website for more information.

Lecture Supplement "Chemistry 313 Supplement", available on Bb

Molecular Model set

May be available in the bookstore and many more are found at a better price from

amazon.com – choose one set suitable for organic chemistry.

Workbook "Organic Chemistry as a Second Language", D. R. Klein (any edition)

Scantrons 4 1/2" x 11", blue (must have VERsion box to bubble in)

None of these materials is required (except Scantrons). However, you will probably be more

successful in the course if you read and study the textbook, attend class and take notes on the

Lecture Supplement, and take advantage of the other suggested resources as necessary to help

you understand organic chemistry. You may choose to use an earlier edition of the textbook;

however, I will not attempt to provide you with a list of changes to the text. All references to the

text are for the current edition.

Resources

This syllabus and all other information pertaining to the course (such as text sections to be

read/omitted, text errors, suggested problems) appear on the course web page (accessed through

http://mason.gmu.edu/~sslayden). The on-line syllabus is the official syllabus for the course.

Occasionally, announcements must be made to the entire class via e-mail. The e-mail will be sent

to your GMU e-mail account.

Copies of exams and the answer keys from a previous semester are available on Blackboard. In

the library are textbooks from which you can supplement your reading and problems. Other

chemistry resources are available on the internet, some of which can be accessed through my

Web site.

You can record the lecture if you wish, but please don’t put the recording device on my desk or

where I can see it.

In the Classroom

You are expected to be on time for class. If you must enter class late, do so quickly and quietly.

You are expected to remain in class for the entire class period. Walking in and out of class is

distracting to the rest of us. It is a courtesy, if you do have to miss class or leave early, to contact

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the professor beforehand and to leave as unobtrusively as possible. If you miss a class, you are

expected to get notes, etc. from other students.

Focus on class material during class time. Sleeping, talking to others, doing work for another

class, reading a newspaper or using an electronic device are unacceptable and disruptive. Cell

phones, pagers, and other electronic communication devices are not allowed in this class. Please

keep them stowed away and out of sight. Do not eat or drink in the classroom. It is difficult, if

not impossible, to take notes or interact effectively while eating. Do not close your books, rustle

your papers, or walk out of the classroom before class is dismissed. These actions are a

distraction and communicate a lack of respect.

Enthusiasm is contagious. Professors respond and teach better to an alert, attentive, and

interested class.

Examinations and Grades

Course Grade: 4 Exams --three exams given during the semester; the fourth exam is given

during final exam week. Each exam is graded as the percentage of questions you answered

correctly. The highest grade possible is thus 100%. The four exam grades are counted equally

and the average of the exams is your final numerical course grade.

Unexcused absence from an exam will result in an assigned grade of zero. If you are unable to

attend an exam, you are expected to talk to me before the exam or as soon thereafter as possible.

(E-mail and voice mail do not satisfy this requirement, although you may leave a message to

alert me.) Documentation for your absence may be required before any consideration is given for

taking a make-up exam, usually during the same week as the originally scheduled exam. Excuses

for “last minute” occurrences that interfered with studying before the exam or that interfered

with attending the exam will not be accepted. Allow enough time for commuting on exam days –

no extra time will be allowed for tardiness, unless there was some catastrophe.

The course web site contains a page of Instructions and Frequently Asked Questions for

taking exams in this course. Please read it.

If classes are canceled by the University on a scheduled exam day, the exam will be given at the

next scheduled class period after classes resume. Hour exams will not be rescheduled (unless

classes have been canceled for an extended period and I notify you). If I am absent for an exam,

another Chemistry Department instructor will take my place.

Make-up Periods for Final Exams

If the university is unexpectedly closed on an exam day, make-up times will be announced as

soon as they are determined and will be posted on the University-wide Class Cancellations page.

The last scheduled day of the final exam period is the scheduled make-up day. The Friday,

Saturday, and Sunday during the final exam period are also potential make-up days. Students and

faculty must be available for the make-up day(s).

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Final letter grades are determined after all numerical grades for all students are calculated

at the end of the semester. Letter grades are not assigned for individual exams. You may

tentatively assume that your exam grade corresponds to a C if it is within approximately +7

points of the number that I define as mid-C for the exam (see the BlackBoard announcement

after each exam). Generally, grades below ~40% are failing grades (F) and grades above 90% are

excellent (A). When each exam is returned, the mid-C and the high and low grades will be

announced on BlackBoard so that you can estimate your standing in the class. The mid-C at the

end of the semester will be the average of the mid-C grades on the exams so you can estimate

your final grade based on your on-going average. The class website link shows a typical grade

distribution chart.

There are no extra credit assignments available for the course. Please do not ask about “curving

grades” if by that you mean some arbitrary number of points might be added to your grade in

order to raise it.

Disability Services

If you are a student with a disability and you need academic accommodations, please see me

after contacting the Disability Resource Center (DRC) at 703-993-2474. All arrangements for

academic accommodations must be initiated through that office.

Honor Code

It is the responsibility of all students to be familiar with the GMU Honor Code. All examinations

are closed book, and the use of notes or other written material is not permitted. A periodic table

will be provided with the exam. You may use, but not share, molecular models during any exam.

You may not use or have in your immediate presence any electronic device.

Academic Policies

The University Catalog is the source of information about all academic policies:

http://catalog.gmu.edu/.

Title IX disclosure

As a faculty member and designated "Responsible Employee", I am required to report to

Mason’s Title IX Coordinator all disclosures a student may make to me of sexual assault,

interpersonal violence, and stalking (University Policy 1412). If you wish to speak with a

“Confidential Employee”, please contact the Student Support and Advocacy Center (703-380-

1434) or Counseling and Psychological Services (703-993-2380). You may also seek assistance

from Mason's Title IX Coordinator (703-993-8730; titleix@gmu.edu).

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INTRODUCTION

“I can produce urea, without having the need for kidneys or an animal at all, be it human being or a

dog. The cyanogen acidic ammonia is urea.”

Letter from F. Wöhler to J. Berzelius, 1828

ISOMERS have identical molecular formulas but have different arrangements of

atoms in their molecules, that is, different structures.

Constitutional Isomers (Structural Isomers) differ in their "connectivity", that

is, in the order of attachment of the atoms in the molecule. These

isomers have different physical and chemical properties.

N

H

H

H

Hheat

ureaammonium cyanate

N C O C

O

N

H

HN

H

H

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Structure

Name dimethyl ether ethanol n-butane isobutane

b.pt. (°C) −24.9 78.5 −0.5 −12

density (g/ml) 0.661 0.789 0.601 0.603

The properties of a substance depend upon its structure.

structure physical & chemical properties

Structure

Bonding

Electrons

Chemical transformations

“Sugar, salicin, and morphium will be produced artificially. Of course, we do not know the way yet by which

the end result may be reached since the prerequisite links are unknown to us from which these materials will

develop—however, we will get to know them.”

F. Wöhler and J. von Liebig

CH3 O CH3CH3 CH2 O H CH3 CH2 CH2 CH3 CH3 C CH3

CH3

H

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ELECTRONIC STRUCTURE OF ATOMS

Atom consists of a dense inner core -- the nucleus (protons, neutrons) -- and

electrons that surround the nucleus.

Particle Relative Mass Charge

proton (p) 1 +1

neutron (n) 1 0

electron (e–) 1/1821 –1

The number of protons in the nucleus (atomic number, Z) uniquely determines the

atom's identity.

In a neutral atom, #p = #e; #n is variable (atomic isotopes).

{ 12

C6

13C

6

14C

6 } {

1H

1

2H

1 D (deuterium) }

isotopes of carbon isotopes of hydrogen

Electrons exhibit particle-like properties (mass) and wave-like properties (diffraction).

Solve

WAVE EQUATION --------> WAVE FUNCTIONS and quantum numbers

Wave Functions express the energies and the positions of electrons in an atom.

Quantum Numbers

n is the designation for the principle, or main, energy level (or energy shell) in the

atom that may be populated with electrons.

The closer an electron is to the nucleus, the less energy it has and

the more stable it is.

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l is an energy sublevel (or subshell) within a given main energy level, n. [ s p d f

sublevels]. There are restrictions on the number of sublevels within a given

main level.

ml is an orbital within a given sublevel. An orbital is a region of space in which an

electron is most likely to be found. [ one s three p five d seven f ]

Orbitals have unique "shapes". Maximum of two electrons per orbital.

ms designates the quantum number for the electron spin. The opposite nature of

their spins differentiates between the two electrons that may occupy a given

orbital (thus having the same n, l, and ml).

Spins may be designated as +1/2, –1/2; “clockwise”, “counterclockwise”;

Pauli Exclusion Principle Each electron in an atom has a unique set of quantum

numbers (n, l, ml, ms)

Atomic orbital chart

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Electron Configuration is the description of the distribution of electrons within an atom. In the ground state,

electrons will occupy the atomic orbitals of lowest energy.

n l#e–

or n ml #e–

H1 = 1s

1 Li

3 = 1s

22s

1 B

5 = 1s

22s

22p

1

Main level (n)

Sublevel

(l)

Orbital

( ml )

Spin

( ms )

Max. #

electrons per

sublevel

Max. # electrons

per main level

1 s s ± 1/2 2

2

2 s s ± 1/2 2

p pxpypz ± 1/2 6

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3 s s ± 1/2 2

p pxpypz ± 1/2 6

d five d's ± 1/2 10

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4 s s ± 1/2 2

p pxpypz ± 1/2 6

d five d's ± 1/2 10

f seven f's ± 1/2 14

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5 * * Although each main energy level contains a number of sublevels

equal to n (verify for n = 1-4, above), main levels 5-7 do not

require more than 4 sublevels to accommodate the electrons in all

known atoms (due to sublevel energy overlap). The sublevels,

orbitals, and electron-occupancy for n = 5-7 will be the same as for

n = 4.

6 *

7 *

10

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Valence Electrons are those electrons that occupy the outermost (highest) main energy level (n) of an atom. They

are the most loosely held and engage in chemical reactions.

Electron Dot Symbols designate the valence electrons (dots) surrounding the inner core electrons and nucleus

(atomic symbol) of an atom.

MAIN BLOCK ATOMS

Hund's Rule In filling degenerate orbitals with electrons, each orbital is occupied singly with electrons of the same

spin; subsequently, electrons of opposite spin are added.

ENERGY LEVEL DIAGRAM

I II III IV V VI VII VIII

A A A A A A A A

Inc.Energy 1s

2s

2px 2py 2pz

SUGGESTED PROBLEMS:

1. Write electron configurations for all atoms Z = 1 - 18.

2. Select a few atoms from problem 1. and show the application of Hund’s Rule by drawing

energy diagrams as shown above.

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Rule of Electronic Stability Electronic stability is greatest when atoms have an n(s

2p

6) configuration in their valence shell and resemble the

closest Noble Gas configuration. The exceptions are elements that can attain the 1s2 configuration more easily than

the s2p

6 configuration, such as H and Li.

Atoms gain, lose, or share electrons in order to achieve this "octet" of electrons.

Mg = 1s22s22p63s2 Mg+2

= 1s22s22p6

Cl = 1s22s22p63s23p5 Cl −1

= 1s22s22p63s23p6

Electronegativity is the tendency of an atom to attract electrons toward itself (to the positively charged nucleus).

E.N. is a periodic property that increases up a family and increases across a row in the Periodic

Table.

Electronegativity B < H < C

For an explanation of the periodic trend, think of the electrons individually,

but think of the nucleus in total:

Electronegativity increases across a row

The positive charge on the nucleus increases as protons are added to the nucleus.

Negatively charged valence electrons are added to the same main energy level.

The effective positive charge of the nucleus increases for all the electrons that are in the

same valence shell and so the attraction between the electrons and the nucleus increases

across the row.

Electronegativity decreases down a column

The positive charge on the nucleus increases as protons are added to the nucleus.

Negatively charged valence electrons are added to main energy levels further from the

nucleus.

Although there is an increase in the number of positive protons in the nucleus, the

increased number of inner electrons screens the effective positive charge on the nucleus

from attracting the outer valence electrons.

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CHEMICAL BONDING

Chemical bond -- the force of attraction that holds atoms together in a molecule.

The force is the attraction between the negatively charged electrons and the

positively charged nuclei. The drive for bond formation is to achieve a filled

valence shell.

Ionic bond – Results from the electrostatic attraction between ions of opposite

charge.

Covalent Bond -- results from sharing of two electrons between two atoms. The

shared electrons are electrostatically attracted to both nuclei.

There are several ways to represent covalent bonding between atoms in a molecule.

Consider the simplest neutral diatomic molecule, H2.

SYMBOLIC REPRESENTATIONS OF COVALENT BOND FORMATION IN H2

1. Lewis Electron Dot Structures

2. AO/MO Pictures

energy released

-435 kJ/mol

1 s atomic orbitals molecular orbital

+K K e- +F e- F

H H HH H H

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Sigma () covalent bonds result from a "head to head" overlap of atomic orbitals

along the internuclear axis.

Any single bond is necessarily a sigma bond (as shown above).

Each of the two atomic orbitals that form the bond can be occupied by one electron or two

electrons can occupy one orbital and the other orbital is empty. (Examples shown later.)

The resulting bonding molecular orbital is occupied by the two electrons.

3. Energy Level Diagrams

Number of Atomic Orbitals = Number of Molecular Orbitals [Conservation of

Orbitals]

*

1s AO

(antibonding MO)

1s AO

(bonding MO)

Unoccupied molecular orbital (antibonding,

*)

Atomic orbitals

Occupied molecular orbital (bonding, )

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Before looking at the representation of bonding in larger molecules, we need to

reconsider the atomic orbitals involved in covalent bonding.

Overview

The energy available in a given main energy level, n, can be distributed into atomic orbitals

occupied by electrons in such a way that the lowest possible energy (the greatest stability) is

associated with the atom.

However, the atomic theory assumptions are not as useful after the atom is bonded with other

atoms in a molecule, and therefore a molecular orbital bonding theory is needed.

To explain the observed molecular bonding patterns in elements in groups II-VI in the first few

rows of the periodic table, we mathematically postulate descriptions of new AO's by

distributing the s and p sublevel energies (for any given main level, n) differently than we did

in the simple non-bonded atom.

These AO's are called "hybrid" AO's as though they were mixtures of the "pure" AO's.

Why is it necessary to invoke hybrid AO’s? Because assumptions about the number of bonded

atoms in a hypothetical molecule are not consistent with the facts. __________________________________________________________________________

Facts

The first molecules we consider are the hydrides of C, B, and Be, all 2nd row atoms. We might

have expected the constitution of these hydrides to be determined by the number of unpaired

electrons in the valence shells of the central atom. For example:

Atom Be B C

Electron configuration Be4 = 1s22s2 B5 = 1s22s22p1 C6 =

1s22s22(px1py

1)

Valence electron atom

dot structure Be

B

C

Molecule assumed to

form with unpaired

electrons

No unpaired electrons

in atomic Be – so no

bonds, no molecule

B H

C H

H

Facts

Be combines with two

H's to form two

identical Be‒H sigma

bonds in BeH2

B combines with

three H's to form

three identical B‒H

sigma bonds in BH3

C combines with four

H's to form four

identical C‒H sigma

bonds in CH4.

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More Facts

Molecules such as ethene and ethyne contain multiple bonds, the constituent bonds of which are

not all identical to each other. For example, in the “double bond” of ethene, H2C=CH2, one of the

bonds is weaker and more chemically reactive than the other and so they must be different kinds

of bonds. Likewise, ethyne, HC≡CH, contains two weaker bonds and one stronger bond. __________________________________________________________________________

Descriptive Explanation of Hybrid Atomic Orbitals

The descriptive process we use to account for the facts above involves taking “pure” atomic

orbitals of an atom and then mathematically “mixing” them together, and dividing the resulting

mixture into new hybrid orbitals.

There are three different sets of hybrid AO's that can be constructed by mixing s and p orbitals in

different proportions. Below is a description of how new, hybrid electron orbitals (sp, sp2, sp

3)

for an atom are constructed from “pure” s and p orbitals. Ignore the electrons for now.

Notice there are always four valence orbitals present, either as pure s and p, or as some

combination of hybrid orbitals and p orbitals.

ENERGY DIAGRAM OF PURE AND HYBRID ATOMIC ORBITALS

[These orbital shapes (including the nucleus “dot”) are somewhat fanciful. See your text and

other sources for better pictures.]

p

s

(sp)

(sp2)

(sp3)

p p

"Pure" AO's for someatom, A

Hybrid AO's for some bonded atom , A

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s p sp sp2 sp3

REVIEW VSEPR THEORY

The spatial orientation of the new hybrid orbital sets can be predicted by imagining the orbitals

are occupied by one or two electrons and are thus negatively charged.

The arrangement of the two sp orbitals will be linear (two mutually repelling negatively

charged orbitals).

The three sp2 orbitals will be trigonal planar, again because of the repulsion of like

charges.

The four sp3 orbitals will be in a tetrahedral arrangement, which is how the four orbitals

can be as far apart as possible.

Summary, in table form, of the chart and information, above.

# of hybrid

AO's

hybrid set unhybridized

p orbitals

approx. geometry of

hybrid orbital set

approx. angle between

hybrid orbitals

2 (sp) 2 linear 180°

3 (sp2) 1 trigonal planar 120°

4 (sp3) 0 tetrahedral 109°

Application

Each hybrid orbital can be occupied by 1 or 2 electrons, just like any other atomic orbital.

If the hybrid AO is occupied by 1 electron, then it can overlap with another atom's AO

(either "pure" or hybrid) to form a sigma bond where the resulting bonding molecular

orbital (MO) contains two shared electrons.

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Just as the “pure” s (and p) atomic orbitals for an atom could overlap and combine to form a

sigma covalent bond between the two atoms, so can a hybrid orbital combine with s, p, and other

hybrid orbitals to form sigma covalent bonds. [Recall the formation of the sigma bond in HH.]

Below are pictures of a few combinations of hybrid and “pure” orbitals to form sigma covalent

bonds. Only the isolated atomic orbitals forming a bonding molecular orbital are shown –

the other orbitals in a degenerate set are omitted for clarity. The unoccupied molecular orbitals

are not shown.

s s

s p

sp2 sp2

s sp3

If the hybrid AO is occupied by 2 electrons that are not shared with another atom, then this

constitutes a non-bonded pair of electrons.

Thus, the set of hybrid orbitals an atom uses in a particular compound depends primarily on how many sigma bonds

and non-bonded electron pairs the atom must accommodate in the final structure.

[A frequent exception to this rule is when non-bonded electrons are on an atom that is adjacent to

a p orbital or pi bond. :AA=A It won’t be discussed this semester.]

The number of hybrid AO's required by an atom in a

molecule =

[# sigma bonds + # non-bonded pairs]

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A single bond is necessarily a sigma bond (why?).

In a double or triple bond, only one bond is a sigma bond; the other bond(s) are pi bonds

as will be seen in the next section.