Mark S. Cracolice
Edward I. Peters
www.cengage.com/chemistry/cracolice
Chapter 12
Chemical Bonding
Mark S. Cracolice • The University of Montana
Monatomic Ions
Noble gas electron configurations are
generally the most stable.
Metal atoms can achieve a noble gas
electron configuration by emptying their
valence orbitals.
Nonmetal atoms can achieve the electron
configuration of the next noble gas by
receiving more electrons on their emptied
valence orbitals.
Monatomic Ions
Lithium atom, which has electron
configuration 1s22s1 can achieve the electron
configuration of helium 1s2 by losing one
electron on orbital 2s, and thus becomes a
cation Li+.
Li
1s22s1
-
e
→
Li+
1s2
Monatomic Ions
Oxygen atom, whose electron configuration is
1s22s22p4, can achieve the electron
configuration 1s22s22p6 of neon by receiving
two more electrons on its 2p orbitals, and
becomes ion O2-.
O
1s22s22p4
+
2e
→
O21s22s22p6
Monatomic Ions
Fluorine atom, whose electron configuration
is 1s22s22p5 can achieve the electron
configuration 1s22s22p6 of neon by accepting
one electron on its 2p orbital, and becomes
anion FF
1s22s22p5
+
e
→
F1s22s22p6
Monatomic Ions
Sodium atom, whose electron configuration is
1s22s22p63s1, can achieve the electron
configuration 1s22s22p6 of neon by giving away
one electron on its 3s orbital, and becomes
cation Na+.
Na
1s22s22p63s1
e
→
Na+
1s22s22p6
Monatomic Ions
Magnesium atom whose electron
configuration is 1s22s22p63s2, can achieve the
electron configuration of neon by giving away
two electrons on its 3s orbital, and becomes
cation Mg2+
Mg
1s22s22p63s2
2e
→
Mg2+
1s22s22p6
Monatomic Ions
Chlorine atom whose electron configuration is
1s22s22p63s23p5, can achieve the electron
configuration of argon by receiving one
electron on its 3p orbital, and becomes ion Cl-.
Cl
+
1s22s22p63s23p5
e
→
Cl1s22s22p63s23p6
Monatomic Ions
Potassium atom (1s22s22p63s23p64s1) can
achieve the electron configuration
1s22s22p63s23p6of argon by losing one
electron on its 4s orbital, and becomes ion K+.
K
e
1s22s22p63s23p64s1
→
K+
1s22s22p63s23p6
Monatomic Ions
Calcium atom (1s22s22p63s23p64s2) can
achieve the electron configuration of argon by
losing two electrons on its 4s orbital, and
becomes ion Ca2+.
Ca
2e
1s22s22p63s23p64s2
→
Ca2+
1s22s22p63s23p6
Monatomic Ions
There are some exceptions to the rules
discussed here. For example tin forms both
Sn2+ and Sn4+
Sn
[Kr]5s24d105p2
Sn
[Kr]5s24d105p2
2e
→
4e
→
Sn2+
[Kr]5s24d10
Sn4+
[Kr]4d10
Configuration with filled sublevel 4d is stable
Monatomic Ions
Lead forms both Pb2+ and Pb4+
Pb
2e
[Xe]6s24f145d106p2
→
Pb2+
[Xe]6s24f145d10
Pb
4e
[Xe]6s24f145d106p2
→
Pb4+
[Xe]4f145d10
Configuration with filled sublevel 5d is stable
Monatomic Ions
Ionic Bonds
Crystal: A solid with a definite geometric structure.
Ionic compounds: compounds made up of ions.
Ionic Bond : The electrostatic forces that hold the
ions in fixed position in the crystal are called ionic
bonds .
Ionic bonds are very strong.
Ionic Bond in sodium chloride
Ionic Bond in sodium chloride
Ionic Bonds
The bonds in an ionic crystal are very strong, which is
why nearly all ionic compounds are solids at room
temperature.
Solid ionic compounds are poor conductors of
electricity because the ions are locked in place in the
crystal.
Only when ionic compounds are melted or dissolved
that the ions are free to move and able to carry
electric current.
Covalent Bonds: Hydrogen molecule
Hydrogen molecule H2
In the hydrogen molecule, the electrons reside
primarily in the space between the two nuclei.
The electron cloud or charge density is concentrated
in the region between the nuclei.
.
Covalent Bond in Hydrogen Molecule
Covalent Bonds: Hydrogen molecule
The simultaneous attraction of each electron by the
two protons generates a force that pulls the protons
toward each other and balances the repulsive force
between protons and repulsive force between
electrons.
.
Covalent Bonds
The type of bonding in which electrons are
shared by nuclei is called covalent bond.
Using Lewis symbols, the formation of hydrogen
molecule can be represented as:
H
+
H
---->
H:H
or
H-H
The two dots or the straight line drawn between the
two atoms represent the covalent bond.
Covalent Bonds
By sharing electrons, each hydrogen atom in
the molecule has two electrons.
Each hydrogen atom has a filled valence shell.
The pair of electrons with opposite spin
shared by two atoms is called bonding pair.
Covalent Bond and ionic bond
Covalent bond: Each atom has a noble gas
electron configuration but shares electron
pair(s) to do so.
Ionic bond: Each ion has its own noble gas
electron configuration
Covalent Bonds
H • + • H®
or
The two dots or the straight line drawn
between the two atoms represent the
covalent bond that holds the atoms together.
Covalent Bonds in F2
Fluorine molecule F2.
Fluorine atom has the following electron
configuration :
1s22s22p5
When two fluorine atoms form a molecule, they
share their unpaired electrons on orbitals 2p,
so that each atom has eight electrons (octet
rule).
Covalent Bonds
A half-filled 2p orbital from one F atom overlaps a
half-filled 2p orbital from the other F atom.
Covalent Bonds
Lewis Diagram, Lewis Formula, Lewis Structure
Electron-dot symbols used to show the bonding
arrangement among atoms in a molecule.
Lone pairs
Unshared electron pairs in a Lewis diagram,
not involved in bonding.
Bonding pair
The pair of electrons shared by two atoms in a Lewis diagram.
Covalent Bonds
Octet Rule
Covalent bonds tend to form between nonmetal atoms by filling
the overlapping valence electron orbitals with the maximum
number allowed, two in the s orbital and two in each of the three
p orbitals, for a total of eight (octa-) valence electrons.
Covalent bonds tend to form
when half-filled orbitals overlap.
Polarity & Covalent Bonds
Nonpolar Covalent Bond
A bond in which bonding electrons are shared
equally by the two nuclei.
The charge density is centered in the region
between the bonded atoms.
A bond between identical atoms is always nonpolar.
Polarity & Covalent Bonds
Polar Covalent Bond
A bond in which the bonding electrons are shared
unequally by the two nuclei.
The charge density is shifted toward one atom
and away from the other.
Polarity & Covalent Bonds
A bond with an unsymmetrical distribution of
bonding electron charge is a polar covalent
bond.
In the hydrogen fluoride molecule HF , the
fluorine atom has a stronger attraction for the
shared electrons than the hydrogen atom.
.
Polarity & Covalent Bonds
The result is that the HF molecule has the following
charge distribution:
Polarity & Covalent Bonds
Electronegativity
Bond polarity in covalent bonds may be described in
terms of the electronegativities of the bonded atoms.
The electronegativity of an element is the ability of
its atom in a molecule to attract shared electrons to
itself
The higher the electronegativity, the stronger is the
attraction of the atom for bonding electrons.
Polarity & Covalent Bonds
The electronegativity is highest at the upper right region of the
periodic table and lowest at the lower left region
Polarity & Covalent Bonds
The polarity of the bond increases as the difference
in electronegativity increases.
For example the following variation in bond polarity is
expected
0
0.4
0.9
1.4
1.9
H-H < S-H < Cl-H < O-H < F-H
Polarity & Covalent Bonds
The polarity of a bond can be estimated by
calculating the difference between the
electronegativity values for the bonded elements.
A C — F bond (4.0 – 2.4 = 1.6)
is more polar than
A C — H bond (2.4 – 2.1 = 0.3)
The bonding electrons are displaced toward the
element with the highest electronegativity value.
Multiple Bonds
Single bond: one electron pair shared.
Double bond: two electron pairs shared.
Triple bond: three electron pairs shared.
Double and triple bonds are multiple bonds.
H
H—H
H
\
/
C=C
/
\
H
H
: N ºN :
H2
C2H4
N2
Atoms Bonded to More Than One Atom
Formation of a Water Molecule From Its Atoms:
Atoms Bonded to More Than One Atom
Additional Molecules with Atoms
Bonded to Two or More Other Atoms:
H
|
H — C —H
|
H
H
\
H
/
C=C
/
\
H
H
H—C
ºC—H
Multiple Equivalent Structures: Resonance
We can write three valid structures for nitrate ion
The nitrate ion is represented by a blend of all structures.
The blended structure is called resonance hybride of three
Lewis structures.
(a mule is a hybride of a horse and a donkey.)
Resonance is a blending of structures with the same
arrangement of atoms but different arrangement of electrons
Exceptions to the Octet Rule
Odd-Electron Molecules
The molecule with one unpaired electron is called a radical.
One of the atoms must have an incomplete octet.
nitrogen monoxide
5 + 6 = 11 valence electrons
nitrogen dioxide
5 + 2(6) = 17 valence electrons
Exceptions to the Octet Rule
Molecules with More Than Four
Electron Pairs Around the Central Atom
Atoms of elements in the third period and higher have empty d orbitals and
big size, can have more than four electron pairs surrounding them:
phosphorus pentafluoride
sulfur hexafluoride
Exceptions to the Octet Rule
Molecules with Fewer Than Four
Electron Pairs Around the Central Atom
Compounds of beryllium and boron are surrounded
by two and three pairs of electrons, respectively:
beryllium difluoride
boron trifluoride
Paramagnetic property of oxygen
Liquid oxygen becomes trapped in the field of a strong magnet
because oxygen molecule has 2 unpaired electrons:
Limitation of Lewis Diagram
Oxygen
No Lewis diagram can be drawn for oxygen that matches
experimental evidence about its paramagnetic property.
Molecular orbital theory can better explain the paramagnetic
property of oxygen molecule.
http://www.mpcfaculty.net/mark_bishop/molecular_orbital_theory
.htm
Metallic Bonds
Metallic Bond
Attractive force between positively-charged
metal ions in a crystal and the negatively-charged
electrons that move among them.
Metallic Bonds
Metallic Bonds
Metals
Electrons in a metal are said to be delocalized
because they are not confined to a localized region
near a single atom or a pair of atoms.
Alloy
A solid mixture of two or more elements
that has macroscopic metallic properties.
Metallic Bonds
HOMEWORK
5, 7, 9, 13, 15, 19, 25, 45.