Chapter 8: Covalent Bonding
I. Matter takes many forms in nature: In this chapter, we are going to learn to distinguish the type of
compound that we have already studied, the “_______________
compound” (which contains oppositely-
charged particles: metal cations and non-metal anions), from a different type of compound – a
“_____________________ compound”. Additionally, we are going to focus on a type of molecular
compound known as a ___________________ molecular compound
II. Binary compounds: A “binary” compound contains _________ from _______ different elements.
A. NaCl”, “CaF2”, and “Al2O3” (3 ionic compounds) are binary ionic compounds. “NH4Cl” is an ionic
compound, but because it contains more than 2 elements, it is _______ a binary ionic compound.
B. “N2O5”, “SF6”, and H2O” (3 molecular compounds) are binary molecular compounds. “C6H12O6” is a
molecular compound, but because it contains more than 2 elements it is ______ a binary molecular
compound.
III. Comparison/Contrast between an ionic compound and a molecular substance.
A. Molecular substances are made of _______________________.
1. There is no “molecule” in an ionic compound.
B. A “molecule” contains a specific _________________ of atoms, connected in a specific manner, to give a
specific shape. If even one atom is “missing” or “different”, the molecule would be an entirely different
substance.
1. Not so with an ionic compound: In an ionic compound there is a specific_____________ of atoms..
In salt (NaCl) for example, there is a ratio of 1 Na for every 1 Cl. If a clump of salt lost 1 Na and 1 Cl,
it would still be the same original substance: NaCl
C. The formula of a “molecule” should never be simplified. C2H8 is not the same substance as CH4.
1. The formula of an ionic compound should always be simplified. Ba2O2 is the same substance as BaO.
D. A molecule will _______ crack apart.
1. Ionic compounds can crack apart if hammered….. If the cations come close too close together and the
anions come too close together, the structure cracks apart.
E. Molecular substances may have _______melting points.
1. All ionic compounds have a very high melting point.
F. Molecular substances may, at room temperature, be found as _______________, __________________,
or _________________.
1. All ionic compounds are solids (at room temperature).
G. Molecular substances contain atoms which are held together by ____________________ bonds.
1. Ionic substances are held together by ionic bonds.
IV. Covalent bonding: The type of bonding that occurs within a molecular substance, in which atoms
______________ their valence electrons in order to become more stable.
A. Occurs between _____________ of ________________________ elements.
B. Not all “molecules” or “molecular substances” are compounds! In addition to the binary molecular
compounds that we will study, there are 7 nonmetallic elements found in nature (in their elemental form) as
pairs of atoms. These are the 7 “______________________” elements:
N2, O2,
F2,
Cl2,
Br2,
I2,
H2.
V. An important review:
A. Metallic elements: Found to the _____________side of the staircase boundary on the periodic table.
B. Non-metallic elements:
1. Elements found to the _____________ side of the staircase boundary on the periodic table.
2. __________________ is a nonmetallic element also.
VI. The octet rule: When a molecule is formed: “Nonmetal atoms _________________electrons in covalent
bonds in order to obtain a full ____________ of electrons.” An octet = 8 valence electrons.
A. Exception: A hydrogen atom will end up with a total of _____ electrons by sharing with 1 other atom.
B. There are a few other notable exceptions to the octet rule:
1. A few molecular compounds which contain an odd number of valence electrons are known to exist.
2. A few molecular compounds have either a boron or an aluminum atom with 6 valence electrons.
a. A few molecular compounds have a central atom with 10 or 12 valence electrons.
(1) One common example is “_____________________ _________________________”. In this
compound, the central sulfur atom contains 6 x 2 = _______ valence electrons. Be sure to
remember that this compound is an example in which the ________________ atom does
_________ follow the octet rule.
VII. Types of covalent bonds.
A. __________________covalent bond – 1 shared pair of valence electrons: 2 dots, or a single dash, represent 2
electrons that are simultaneously being attracted by, or “shared” by, the nuclei of two neighboring atoms.
1. The formula in the center is a type of structural formula called a “Lewis dot structural formula”.
2. The formula on the right is the molecular formula.
H–H
H H
H2
B. ______________________covalent bond – two pairs of shared valence electrons: 4 dots or 2 parallel
dashes.
H
H
C
H
H
C
H
C
H
H
C
H
C2H4
C. ___________________ covalent bond – three pairs of shared valence electrons: 6 dots or 3 parallel
dashes.
N
N
or
N
N
N2
Notice the two “_______________________ pairs” of electrons (one pair is to the far left and one pair to the far
righ)t of the nitrogen structure. You may never use a long dash to represent an unshared pair of electrons.
Unshared pairs OF electrons don’t bond the atoms together….but, the repulsive forces of unshared pairs of
electrons do dramatically influence the _______________ of a molecule!
D. Notice how an ion can react with a molecule to generate a polyatomic ion. In the example below, a
hydrogen ion bonds to a molecule of ammonia(NH3) to make the ammonium ion (NH4)+:
+
H
+
Note:
H+ is a hydrogen ion,
a nucleus with 0 electrons!
H
N
H
H
H
H N H
H
+
VIII. Drawing a Lewis Dot Structure:
A. Certain elements are known as “central” atoms…. They will be found in the center of a structure. The
first element given in a formula is usually the central atom (exception: hydrogen and the halogens).
1. Position the central atom in the center of your work space.
B. Hydrogen and the halogens are known as “peripheral” atoms. They will be found only connected to one
other atom. Position hydrogen and halogen atoms so that they “touch”, or “go around” only 1 other atom.
C. Add up all the valence electrons. Position the valence electrons as dots around the atom they belong to the valence electrons may never leave the original atom. Position the dots to form a “doorway” with 4
sides, in which the symbol of the element appears centered in the doorway. Start with no more than 2 dots
on each side of the 4 sided doorway.
D. If you can’t easily achieve a Lewis dot structure which has each atom (other than hydrogen) surrounded
by 8 dots by doing what is described above, then you either need a double bond (2 pairs of shared electrons)
or a triple bond (3 pairs of shared electrons). For CO2, you will need two double bonds.
1. To make a double bond, move one “un-shared electron” simultaneously from each of two neighboring
atoms, and place those 2 electrons in between the two neighboring atoms.
2. To make a triple bond, start with a double bonded pair of atoms, and simultaneously move one more
unshared electron from each of the two atoms. Reposition those two electrons in between the atoms.
E. Important points regarding nonmetal atoms and their bonding charcteristics:
Atoms of the
Have This Number of Type of Bonds
Things to Remember about atoms of
Following
Electrons (dots) When Permitted by these
these elements; or to remember about
Nonmetallic Elements: in a Stable Structure:
atoms:
a specified molecule.
Hydrogen
2
Single covalent
Boron, Aluminum
8 or 6
Single covalent
Sulfur
8 EXCEPT with
“SF6” when there
are 12
8
Single, double, and/or
triple covalent
The Halogen family:
F, Cl, Br, I, At
Single covalent
The Noble Gas family: 8….Except for
helium (2). Noble
gas atoms don’t
form compounds.
Nitrogen and oxygen
8
Do NOT form
compounds easily (no
bonds).
All other nonmetal
atoms
Single, double, and/or
triple covalent
8
Diatomic element;
H2 is a “linear” diatomic molecule
When only 6 electrons surround a
boron or an aluminum atom, the
molecule’s shape will be “trigonal
planar” (a flat pancake).
In sulfur hexafluoride sulfur does
NOT follow the octet rule. This is one
“exception” to the octet rule.
All are diatomic elements; and,
F2, Cl2, Br2, I2, At2 are all linear
molecules, with only single bonds.
Always found as single atoms in the
gaseous state.
Single, double, and/or
triple covalent
Diatomic elements; linear molecules.
N2 has one triple bond, while O2 has 1
double bond.
Ex: Lewis dot structural formula for a compound with this Molecular formula: C2Cl6
Lewis dot structural formulas:
Structural formula:
Cl
Cl
Cl
C
C
Cl
Cl
Cl
Cl
Cl
Cl
C
C
Cl
Cl
Cl
Cl
Cl
Cl
C
C
Cl
Cl
Cl
IX. Lewis Dot structural formulas for polyatomic ions:
A. Covalent bonds occur _________________a polyatomic ion (______
_____________ polyatomic ions).
B. When drawing polyatomic ions, place the _________________ element in the _________________ of the
structure, and place the second element ___________________ the first element (placing 1 atom of the
second element along each different _____________ of the first element).
C. When the charge of a polyatomic ion is +, you need to _______________________the indicated number
of electrons from the total of the valence electrons in the molecule. So, for +1 ions: take away _____
electron from the molecular ion’s number of valence electrons.
D. When the charge of a polyatomic ion is –, you need to _____________the indicated number of electrons
to the molecular ion’s number of valence electrons.
1. If the charge is 1-, then add _____ more electron to the molecule’s total number of valence electrons.
2. If the charge is 2-, then add ____more electrons; if the charge is 3-, then add ____ more electrons.
E. Last, for a polyatomic ion: Draw a large __________________around the ion; and, place its charge at
upper right.
Ex: Ammonium Ion:
# of N valence electrons =
# of H valence electrons =
+
H
H N H
H
Practice spaces for drawing NO2
5
4x1=
+4
Charge of ion = 1+ therefore, less 1 electron =
-1
Therefore total valence electrons =
8
–
Practice space for assigned other polyatomic ions:
While there are no test questions on
this, NO2 – forms a special type of
molecule called a “resonance”
structure, and has a special type of
bond called a “coordinate covalent
bond”.
X. VSEPR Theory – Valence Shell Electron Pair Repulsion theory. [Remember: Like charges repel!]
A. A theory to predict the 3-dimensional geometry, ie. the“_________________” of a molecule
1. The theory is based on “electrostatic repulsion”: Molecules will adjust their ______________to keep
the negatively-charged pairs of _______________________electrons as _____________
______________ as possible from each other.
B. When NOT to use ___________ theory: When there are only 2 atoms in a molecule. These
molecule’s shapes are called _________________ – it doesn’t matter if there are single bonds, double
bonds, triple bonds, or unshared electron pairs.
C. Using VSEPR theory:
1. Draw the Lewis
________ ________________ for the molecule.
2. Identify its __________________ atom.
3. Identify the sets of valence electrons as one of two possibilities:
a. Those ________________________ two atoms.
b. Those that do not connect two atoms. These are called “_________________pairs”.
4. The unshared pairs found on a central atom strongly ______________ each other; and molecules
that would otherwise be linear, will be forced into a _________________ (or _________________)
shape.
5. Unshared pairs also cause a molecule that would be shaped like a flat triangle (__________________
___________________), to be forced into a ______________________
( __________________
___________________________) shape.
6. __________ the number of connections separately from the number of unshared pairs.
1 single bond counts as ____ connection.
1 triple bond counts as ___ connection.
1 double bond counts as ____ connection.
Each unshared set of 2 dots counts as ____ un-shared pair.
D Predicting Shapes Using VSEPR Table Read horizontally across the table.
Connections To
the Central Atom
Unshared Pairs of Electrons
Around Central Atom
2
3
4
2
3
0
0
0
1 or 2
1
Molecular Shape
Around Central Atom
Linear
Trigonal Planar
Tetrahedral, 109.5o
Bent
Pyramidal
E. Shapes:
Trigonal Planar
Bent
Linear diatomic
Linear triatomic
Pyramidal
Tetrahedral
XI. “Molecular Polarity” – A term that is used to distinguish two types of molecules…. Based on the
presence or absence of a ______________________ of ____________________.
A. Some molecules show characteristics indicating that they have ______________________-charged ends
(a positive end and a negative end). This is called a separation of the charges (or “separation of charge”).
B. Other molecules show characteristics indicating that their structure doesn’t have a separation of charge, or
their structure hides the presence of their oppositely-charged ends.
XII. How to determine a molecule’s polarity.
A. The first part of determining a molecule’s polarity is to calculate each individual bond’s polarity.
1. Be careful with the vocabulary being used –
a. An individual bond’s polarity is called the “_____________
___________________”.
b. The polarity of the entire molecule is called the “_____________________ ________________”].
2. To calculate a bond polarity, first identify the “_____________________________ value” of each of
the 2 atoms in the bond you are working on.
a. The electronegativity value is number (from 0 to 4) which informs us of an atom’s ability to
____________________ electrons when in a compound.
(1) The electronegativity value is given on your periodic table, side 2, within each element’s
square…..upper right corner of the square, in black print.
(2) The closer an element’s electronegativity is to “______”, the better that an atom of that
element will attract electrons when that atom is found in a compound.
(3) The closer an element’s electronegativity is to “_______”, the ______ likely it is for that atom
to be able to attract electrons when in a compound.
3. After identifying the two electronegativity values, subtract the two electronegativity values. Take the
absolute value of the answer (make the answer positive).
4. After subtracting and taking the absolute value of the two electronegativity values, then think
about your answer, and determine whether your answer indicates that there is, or that there is not,
a situation in which one of the two atoms in the bond “overpowers” the other atom in terms of
electron attracting ability. If an atom is able to overpower the other atom, it will “hog” the electrons,
as opposed to sharing the electrons equally with the other atom. You will see (on the next page) that
I’ve placed a “δ–”sign next to an oxygen atom, and a “δ+” sign next to 2 hydrogen atoms, in a sketch of
a water molecule. By doing this, I am indicating that the oxygen atom is hogging the negativelycharged valence electrons belonging to the 2 hydrogen atoms; and, the 2 hydrogen atoms are both
overpowered and “partially lose” their own valence electrons to the oxygen atom.
a. ____ indicates the “partial negative” atom; and, ____ indicates the “partial positive” atom.
5. Finally, you are now able to conclude that a bond is either “nonpolar covalent” or “polar covalent”.
a. A bond is to be called “__________________ covalent” when the two atoms share the electrons
more-or-less ________________.
(1) Labeling a bond as nonpolar covalent means that the difference in electronegativity values
fell between 0 and 0.4
(2) Labeling a bond as nonpolar covalent means that the electrons are distributed practically
equally along the bond.
(3) Labeling a bond as nonpolar covalent means that there is no separation of charge in that
particular bond.
b. A bond is to be called “_________________ covalent” when the electrons are NOT distributed
equally along the bond, rather, the electrons are found much or most of the time toward the atom
that has the higher electronegsativity value.
(1) This will occur when difference in electronegativity values is greater than 0.4, but less than 2.
(2) We place a δ – next to an atom to identify it as the “partial negative” atom; and, we place a δ
+ next to an atom to identify it as the “partial positive” atom in a polar covalent bond.
c. A bond is designated as ________________ when one atom has stripped the other of some of its
valence electrons, yielding a cation and an anion. Then, the cation and anion are attracted, and more
cations and anions are attracted and an ionic compound forms.
(1) This should occur when the difference in electronegativity values is greater than 2.
(2) We studied this type of compound previously. Ionic compounds have very different
characteristics than compounds in which polar covalent and nonpolar covalent bonds exist.
XIII. Summary Chart:
Subtraction Answer ( │EN – EN│ )
Type of Bond
0
0.4 (including 0.4)
Non-Polar Covalent Bond
0.4
2.0 (over 0.4; including 2)
Polar Covalent Bond –
Indicated by inserting a δ +
and a δ – at the appropriate
ends of a polar bond.
> 2.0 (over 2)
δH+
δ
2.20
O
3.44
δ
δH+
2.20
Ionic Bond
XIV. The second part of determining the “molecular polarity” (a molecule’s polarity) is visualizing the
effect of the individual bond polarities in conjunction with the ______________ of the molecule. Some
common occurrences are listed below:
A. If the molecule’s shape is either ____________________, ___________________ __________________,
or ________________________ ____________________, and if all the bonds in the structure are
identical, then the overall molecule’s polarity (the molecular polarity) is ___________________.
1. This is because, if every bond is nonpolar, there isn’t a substantial separation of charge to begin with.
2. And, if every bond is polar (as long as each bond has the same 2 atoms), the polarity of each bond will
be __________________ due to the symmetry of the polar bonds around a central atom. When this
symmetry exists, the δ – charge(s) ______________________the δ + charge(s) in each bond.
B. If the molecule’s shape is either __________________ or ______________, and the structure contains
non-identical bonds in which 1 is polar, then the overall (molecular) polarity is polar (because 1 polar bond
won’t have another bond to be cancelled with).
C. If the molecules’ shapes are pyramidal or bent, and one or more of the bonds is polar, the overall
(molecular) polarity is “_____________________”. This is because in molecules having these shapes, the
bond polarity is not situated symmetrically relative to the molecule’s center, so the polarity doesn’t cancel.
To save space, I have omitted the “δ” signs in the diagrams below.
D. Polar bonds NonPolar molecule
Polar bonds combine to cancel out;
Producing Non-polar molecules:
-
+
-
Polar bonds  Polar molecule.
Polar bonds do NOT cancel out;
Producing Polar Molecules:
+
Bent
+
+
-
Linear triatomic
-
+
+
-
-
Trigonal planar
(flat triangle)
- - +
+
-
-
+
+
+
Linear diatomic
Tetrahedral
Tetrahedral
Pyramidal
+
+
+
+
Linear triatomic
+
+
-
XV. “Like dissolves like”:
A. An expression stating that ______________ compounds and molecules whose molecular polarity is
___________________ will be able to dissolve only in solvents containing _____________________
molecules; and, conversely molecules whose molecular polarity is ___________________________ will
be able to dissolve only in solvents containing ______________________ molecules.
XVI. Some characteristics of a water molecule:
A. A H2O molecule has 2 identical polar bonds, a bent structure, and
its molecular polarity is “polar”.
B. The partial negative (or slightly negative) region of a water
molecule is the area closest to the ____________________ atom.
δ
O
3.44
δH+
2.20
δ
δH+
2.20
C. The partial positive (or slightly positive) region of a water molecule lies within the area closest to the two
_____________________ atoms.
D. Because of having the above characteristics, water behaves in an unusual manner:
1. When placed between a positively charged metal plate and a negatively charged metal plate, the water
molecules all line up, with their _____________________-charged region attracted toward the negative
plate and their ______________________ charged region attracted toward the positive plate.
XVII. _________- molecular Bonds (or forces of attraction) are DIFFERENT from the covalent bonds you
have been studying so far!
A. The covalent bonds you have been studying so far (single, double, triple bonds) are bonds
________________
a molecule; these would be called______ __-_______________________bonds.
B. ___________-molecular bonds (forces) are the attractions _________________2 molecules. They
hold __________________________ molecules together.
C. They are __________________ than polar and non-polar covalent bonds (single/double/triple).
D. They are ___________________than the ionic bonds which connect cations to anions.
E. Breaking an inter-molecular bond is a _____________________ change; whereas, breaking an intramolecular bond is a chemical change.
1. When you boil water (to generate water vapor), or melt ice (to generate liquid water), you are breaking
inter-molecular bonds. When you treat a water molecule with electricity, you destroy the water
molecule and generate from it oxygen gas and hydrogen gas….this is the breaking of intra-molecular
bonds….this is a chemical change.
XVIII. Types of intermolecular bonds:
A. _______________________ bond: Is the _______________ intermolecular force; and, it is perhaps the
most important intermolecular bond, as it is necessary for life as we know it.
1. Hydrogen bonds take effect when you have a combination of a few certain atoms in a polar molecule.
2. The ________________ molecule must contain a _____________________ atom, and that hydrogen
atom must be connected to one of the highly electronegative atoms listed below:
a. ____________________, ____________________, OR __________________.
b. Ex: H2O, HF, NH3
3. Hydrogen bonds determine the properties of water and biological molecules (such as proteins).
a. Cause water to predominate as a _____________________ (rather than as a gas) on earth.
b. Cause ice to ___________________upon freezing (rather than contract as the kinetic molecular
theory would predict).
c. Holds the________________ double helix structure together.
B. Time-permitting, we will also learn about one of the weaker types of intermolecular forces of attraction by
doing a lab in which we use evaporation rates to identify between hydrogen bonding and a weaker force,
present between nonpolar molecules.