Ch4.12.bonding molgeo

Chemical Bonding: The Ties that Bind
Carbon exists
commonly as charcoal,
coal, peat and soot.
When soot is subjected
to high temperature and
pressure, it can form
diamond. This process
can be explained by
understanding the
chemical bonds that
hold the atoms
together.

© 2013 Pearson Education, Inc. Chapter 4 1

Stable Electron Configurations
Fact: Noble gases, such as helium, neon, and argon are
inert, they undergo few if any, chemical reactions.
Theory: The inertness of noble gases results from their
electron structures; each (except helium) has an octet of
electrons in its outermost shell.
Deduction: Elements become less reactive when they
alter their electron structures to that of a noble gas.


Sodium can lose a valence electron. After doing so, its
core electrons are configured like the noble gas neon.


Chlorine can gain an electron, and in doing so, its
electron structure becomes like argon.


Lewis (Electron Dot) Symbols
G. N. Lewis developed a
method of visually
representing the valence
electrons as dots around the
symbol of an atom.
1)What is a valence electron?
2)Why do some atoms “lose”
valence e-s while others “gain”
them?q


Lewis (Electron Dot) Symbols


Sodium Reacts with Chlorine (Fact)


Sodium Reacts with Chlorine (Theory)


Sodium Reacts with Chlorine (Theory)
Na+ ions and Cl- have opposite charges and attract each
other. The resulting attraction is an ionic bond.
Ionic compounds are held together by ionic bonds and
exist as crystal lattice.


Atoms and Ions: Distinctively Different


Octet Rule
In chemical reactions, atoms tend to gain, lose, or share
electrons so as to have eight valence electrons. This is
known as the octet rule.
A little bit of relevant history about Dmitri Mendeleev:
http://web.lemoyne.edu/~giunta/ea/mendeleevann.html


Octet Rule
Metals lose electrons to take on the electron structure of
the previous noble gas. In doing so, they form positive
ions (cations).

Nonmetals tend to gain electrons to take on the electron
structure of the next noble gas. In doing so, they form
negative ions (dogions)..uh nope, that would be anions.


Octet Rule


Formulas and Names of Binary
Ionic Compounds
Cation Charge: The charge of a cation from the
representative elements is the same as the family
number.
The name of a cation is simply the name of the element.
Examples:
Na+ = sodium ion
Mg2+ = magnesium ion


Ionic Compounds
Anions: The charge of an anion from the representative
elements is equal to the family number minus eight.
The name of an anion is the root name of the element
plus the suffix –ide.
Examples:
Cl- = chloride ion
O2- = oxide ion


Ionic Compounds
To name binary ionic compounds, simply name the
ions.

Examples:
NaCl = sodium chloride

MgO = magnesium oxide


Ionic Compounds
Many transition metals can exhibit more than one ionic
charge. Roman numerals are used to denote the charge
of such ions.
Examples:
Fe2+ = iron(II) ion
Fe3+ = iron(III) ion
Cu2+ = copper(II) ion
Cu+ = copper(I) ion


Ionic Compounds
Commonly Encountered Ions


Covalent Bonds
Many nonmetallic elements react by sharing electrons
rather than by gaining or losing electrons.

When two atoms share a pair of electrons, a covalent
bond is formed.

Atoms can share one, two, or three pairs of electrons,
forming single, double, and triple bonds.


Names of Binary Covalent
Compounds
Binary covalent
compounds are named
by using a prefix to
denote the number of
atoms.


Compounds
Binary covalent compounds have two names:

1. First name = prefix + name of 1st element
(Note: If the first element has only one atom, the
prefix mono- is dropped.)

2.Second name = prefix + root name of second element
+ suffix –ide.


Compounds
Easy Examples:
SBr4
sulfur tetrabromide

P2O3
diphosphorus trioxide


Electronegativity
Electronegativity is a measure of an atom’s attraction
for the electrons in a bond.


Polar Covalent Bonds
When two atoms with
differing
electronegativities form
a bond, the bonding
electrons are drawn closer
to the atom with the
higher electro-negativity.
Such a bond exhibits a
separation of charge and
is called a polar covalent
bond.


Bond Polarity

Bond polarity can
be represented on
a Lewis structure
with either the
partial symbol or
with the arrow as
shown at the
right.


Bond Polarity
The difference in Δ EN Type of
electronegativity Bond
between two bonded
atoms can be used to < 0.5 Nonpolar
determine the type of covalent
bond. Use the adjacent
Between 0.5 Polar
table as a rule of thumb.
and 2.0 covalent

Greater than Ionic
2.0


Polyatomic Ions

Polyatomic ions are groups of covalently bonde
atoms with a charge.


Writing Formulas Using
Polyatomic Ions
When writing formulas for compounds containing
polyatomic ions, it may be necessary to use parentheses
to denote the proper number of the ions.

Example: calcium nitrate
Ca2+ NO3-

Ca(NO3)2


Naming Compounds with
Polyatomic Ions
When naming compounds with polyatomic ions, simply
name the ions in order.

Example: (NH4)2SO4

ammonium sulfate


Rules for Sketching Lewis
Structures
1. Count valence electrons.
2. Sketch a skeletal structure.
3. Place electrons as lone pairs around outer atoms to
fulfill the octet rule.
4. Subtract the electrons used so far from the total
number of valence electrons. Place any remaining
electrons around the central atom.
5. If the central atom lacks an octet, move one or
more lone pairs from an outer atom to a double or
triple bond to complete an octet.


Sketching Lewis Structures


Odd Electron Molecules: Free
Radicals
An atom or molecule with an unpaired electron is
known as a free radical.

Examples include:

NO NO2 ClO2


Molecular Shapes: The VSEPR
Theory
The Valence Shell Electron Pair Repulsion (VSEPR)
theory predicts the shape of molecules and
polyatomic ions based on repulsions of electron pairs
on central atoms.


….and then there was Spaceballs with
Princess Vespa!


VESPA


Theory


Shapes and Properties: Polar and
Nonpolar Molecules
In order for a molecule to be polar, two
conditions must be met:

1. It must have polar bonds.

2. The bonds must be arranged such
that a separation of charge exists.


Shapes and Properties: Polar
and Nonpolar Molecules


Nonpolar Molecules


Ammonia
• What is NH3(g)?
• Hmmm…what is (NH4)1+(aq)
• Which one smells bad?

Ammonia Manufacturing Plant

Only the lone pairs know the way I feel today…
Only the lone pairs…
© 2013 Pearson Education, Inc. Chapter 4 Know this feelin’ ain’t right… 42

Common Molecular Geometries…..with a
Central Atom


Determining Bond Angles in a Simple
Molecule…a Rule of Thumb
• What about when there
are lone pairs of
electrons, (non-bonding
pairs) on the central
atom in a molecule of a
part of a molecule?
• In general a bond angle
is compressed 2o for each
pair of electrons.


Nonpolar Molecules


Chemical Vocabulary


Water: The Case of a Bent Molecule!
• Example: Water
The ideal H-O-H bond angle is 109.5o
The experimental H-O-H bond angle
is 104.5o
• Why does the bond angle change?


Meanwhile in Elizabethan England…Dickens
ponders a sequel novel… “A Tale of Three
Molecules: Carbon Dioxide,
Tetrachloromethane and Formaldehyde”
Chuck

Take it from me, “Mr. Hyde”…
formaldehyde is really dreadful
stuff…ycchh!

http://images.google.com/imgres?
imgurl=http://wps.prenhall.com/wps/media/objects/602/616516/Media_Assets/Chapter10/Text_Images/FG10_0103UN.JPG&imgrefurl=http://wp
s.prenhall.com/wps/media/objects/602/616516/Chapter_10.html&h=434&w=1600&sz=81&tbnid=HFA_cJDb76cJ:&tbnh=40&tbnw=147&start=2
© 2013 Pearson Education, Inc. Chapter 4
&prev=/images%3Fq%3Dcarbon%2Bdioxide%2Bdipole%26hl%3Den%26lr%3D 49

Predicting Molecular Polarity: Carbon
Dioxide, Tetrachloromethane &
Formaldehyde
1) For each of the molecules in the previous slide identify each bond in the
molecule as either polar or non-polar. (BTW: If the difference in
electronegativity for the atoms in a bond is greater than 0.4, we consider
the bond polar. If the difference in electronegativity is less than 0.4, the
bond is essentially non-polar.)
2) If there are no polar bonds, the molecule is non-polar. If the molecule has
polar bonds, move on to Step #4.
3) If there is only one central atom, examine the electron groups around it.
4) If there are no lone pairs on the central atom, and if all the bonds to the
central atom are the same, the molecule is non-polar. If the central atom
has at least one polar bond and if the groups bonded to the central atom are
not all identical, the molecule is probably polar. Move on to Step #7.
5) Draw a geometric sketch of the molecule. (3-D wedge, line & dotted line)


Predicting Molecular Polarity…continued!

7) Determine the symmetry of the molecule using the following steps:
a) Describe the polar bonds with arrows pointing toward the more
electronegative element.
b) Use the length of the arrow to show the relative polarities of the
different bonds. (A greater difference in electronegativity suggests a
more polar bond, which is described with a longer arrow.)
c) Decide whether the arrangement of arrows is symmetrical or
asymmetrical If the arrangement is symmetrical and the arrows are of
equal length, the molecule is non-polar. If the arrows are of different
lengths, and if they do not balance each other, the molecule is polar. If
the arrangement is asymmetrical, the molecule is polar.
d) Try your skills…goto…ChemTeam…

http://dbhs.wvusd.k12.ca.us/webdocs/Bonding/Molecular-Polarity.html

http://www.mpcfaculty.net/mark_bishop/molecular_polarity_study_sheet.htm

Polarity: The Truth
Introduction:
• The polarity of a molecule is the sum of all of the bond
polarities in the molecule.
• Since the dipole moment (m, measured in Debyes (D)) is a
vector (a quantity with both magnitude and direction), the
molecular dipole moment is the vector sum of the individual
John Roberts, Chief
Justice, Supreme Court
dipole moments.
• Remember Dicken’s sequel? Well…if we compare the
molecular dipole moments of formaldehyde and carbon
dioxide, both containing a polar carbonyl (C=O) group, we
find that formaldehyde is highly polar while carbon dioxide
is non-polar. Since CO2 is a linear molecule, the dipoles
cancel each other.
• Now…Draw a reasonable Lewis structure for these
molecules.

FYI: If you’re really motivated to learn about how dipole
moments are calculated..goto this link:

http://www.chemistry.mcmaster.ca/esam/Chapter_7/section_3.html

Quick, let’s make our getaway or we’ll be
Lost in the Ozone Again!!!
• http://earthobservatory.nasa.gov/
Newsroom/NewImages/images.ph
p3?img_id=5189

• Decomposition of Ozone movies:
CL2F2; NO
• http://cwx.prenhall.com/petrucci/mediali
b/media_portfolio/15.html
• Great Ozone 3-D Geometry site:
• http://www.elmhurst.edu/~chm/vchembo
ok/206bent.html

Expanded Octets …(uh duz that mean like 9 or 10?)

• OK…there is this compound called Xenon tetrafloride.
• Is it covalent?
• How do you know?
• What is the central atom in the structure? Lewis Structure
• How do you know?
• Is the Lewis Structure at the right “correct”? Why/ Why not?

Consider the following:
1) When you make a Lewis Structure for a molecule of a
compound you first determine the sum of the valence
electrons for each atom represented in the empirical formula
of the compound. For XeF4 that would be (8)Xe + (4 x 7)4F = 3-D Structure
36e-s.
2) Doing some simple math, XeF4 requires four bonds, one each
for each Xe-F bond, (4 total). That requires 4 x 2 = 8 e-s

3) This gets complicated because Xe has a full valence shell,
with no single electrons available for forming bonds.
However, if you split two of the pairs on Xe you get four,
single electrons available for forming bonds.

XeF4 & Expanded Octets continued….

4) Following this logic, make a single bond with each F atoms connected to a
central Xe atom. Recall that each F atom has 7 valence e -s, (three pairs and
one single). Sharing a single e- with Xe results in four covalent bonds and
four octets, (one octet around each F atom).
5) Doing simple e- math again we calculate 4F atoms x 8e-s = 32e-s for the F
atoms. We have two pairs, (or four e-s), remaining around our central Xe
atom. What the heck do we do with them??? Besides, we already have an
octet around Xe and each F atom!
6) Aha!! Many atoms expand their octet. Only atoms with d orbitals can
expand their octet. This requires that the atom have a principal quantum
number, (n), of 3 or more. Therefore these atoms will be in the third or
higher period of the periodic table and have an atomic number of 12 or
more.
Note: Although these atoms can expand their octet, they do not always do so.
Only the central atom will expand its octet. After drawing a Lewis
structure in the normal way, if the formal charges on the molecule are
decreased by creating a double bond, the double bond will form.


Formal Charge
Introduction
A hydrogen atom is made up of one proton and one electron. The formal
charge of the atom, the sum of the charge of the proton and the charge of
the electron, is zero. The formal charge on any atom is zero when the
number of protons (the atomic number) and the number of electrons that
"belong" to that atom are equal. We have seen that it requires 13.6 kcal/mol
to separate an electron from a hydrogen atom. The resulting hydrogen
nucleus, the proton, has a formal charge of +1.
Assigning formal charges to isolated atoms and ions is easy. So is
assigning formal charges to atoms that are covalently bonded within
molecules.

Calculating Formal Charges
To determine the formal charge of an atom within a molecule, separate the
atom from its bonding partner(s), dividing all bonding electrons equally
between the bonded atoms. Then compare the number of electrons that
"belong" to each atom to the atomic number of that atom. Figure 1uses
color coding to illustrate the procedure for methane, CH 4.


Formal Charge Example: Methane
1) Each hydrogen is assigned one of
the two electrons it shares with
the central carbon atom; the
formal charge on each hydrogen
atom in methane is zero.
2) The central carbon is assigned
one of the two electrons it shares
with each of the four hydrogens.
These are its four valence
electrons. But the carbon atom
also has two inner shell electrons
to consider.
3) The total number of electrons
assigned to the carbon is six; this
is the same as the atomic number
of carbon, and the formal charge
on the carbon atom is zero.

Chem Team formal charge tutorial:
http://dbhs.wvusd.k12.ca.us/webdocs/Bonding/FormalCharge.html
© 2013 Pearson Education, Inc. Chapter 4
http://www.usm.maine.edu/~newton/Chy251_253/Lectures/Formal%20Charge/FormalCharge.html 57

Hmmm…Back to XeF4
1) What is the formal charge on each F atom? (0, +1)
2) What is the formal charge on Xe? (Did you get 0? -2?)
3) If the formal charges are zero…there is no reason to alter the
suggested structure. If the formal charges are not zero, then
you should attempt making double bonds to reduce formal
charges on the atoms in the strucrure, more especially the
central atom.
4) Now…consider the polyatomic ion, (ClO3)1-.
a)
5) Which structure at the left, “a” or “b”, is correct? Explain
6) What is the geometry of the correct structure?
7) Check this web site for the answer:

http://www.up.ac.za/academic/chem/mol_geom/mol_geometry.htm
b)


Mr. “T” & Your Microwave Oven
• So you just put the food into the microwave, press
the “start” button in and PRESTO! it heats it up. But
why does it heat the food yet it doesn't heat the dish,
and why is the inside of the oven always cold?
• Mr. “T” sez…”I pity the fool who doesn’t know that
a microwave oven has a magnetron in it. (A
Mr. “T”, AKA, “Mr. Science” magnetron is actually a type of radio transmitter. If it
asks us to consider: How does
the microwave in your kitchen
was on a radio mast, (antenna), (don't try this), it
work? would be able to send radio signals a long way. But it
is inside a metal box, (your microwave oven), which
keeps the signal in.”
• Mr. “T” sez…”Microwaves can put bad megahertz
on you if you mess around with them. So kids…if
you don’t want megahertz from me….don’t mess
around with the microwave oven!”
• The frequency of the transmitter is 2450MHz
(megahertz), which is a wavelength of 12cm (that's
why it's micro waves, rather than short waves
(several meters), medium waves (hundreds of meters)
or long waves (thousands of meters). There's a good
reason for the frequency being 2450 Megahertz,
which I'll explain.

Microwave Oven II
• Hey kids…food has lots of water in it, you
know… H2O.
• A water molecule has the O (Oxygen) in
the middle, and the two H's (Hydrogen)
stuck on it like Mickey Mouse ears at a
Mickey Mouse
particular angle… (105o). Hey you..yup you there in
• The H's are positive and the O is negative, the back row. Pay
so the molecule has a + and - end. It has attention!
"polarity".
• Hey…how come this is true?
• True or False?: Polar molecules line
themselves up in an electrical field.
• In your microwave oven the electrical field
is changing 2,450 million times a second!
• The water molecules don't quite have time
to line up one way before they have to try
to line up the other way! http://images.google.com/imgres
?
• So, anything with water in it has all these imgurl=http://library.thinkquest.
molecules being moved this way and that org/C004535/media/water_diagr
way by the electrical field, and heated up. am.gif&imgrefurl=http://library.t
hinkquest.org/C004535/propertie
WHY??? The dishes, walls of the oven, etc, s_of_water.html&h=161&w=16
don't pick up radio waves, so they don't get 6&sz=3&tbnid=U7Ursf5iscJ:&t
heated up. bnh=90&tbnw=92&start=13&pr
ev=/images%3Fq%3DMickey
© 2013 Pearson Education, Inc.
http://www.zyra.org.uk/microw.htm Chapter 4 %2Bmouse%2Bwater%26hl 60

You Write the Captions…

• http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/me
dia_portfolio/text_images/CH10/FG10_08a.JPG Chapter 4 61

Water

Striper Fishin’ at Lobstahville

The Bessegan, Norway

What is the maximum density of
water?
What would happen if water was
most dense at 0oC?
What would happen if water was
non-polar? Old Time Hockey, Milt Schmidt
http://home.online.no/~slunde/gbess1199.jpg Chapter 4 62

Ch4.12.bonding molgeo

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