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Chapter 8
Chemical Bonding
© 2009, Prentice-Hall, Inc.
Chemical Bonds
• Three basic types of bonds
– Ionic
• Attraction between positive
and negative ions
• Transfer of electrons from
one atom to another
– Covalent
• Sharing of electrons
• Orbital overlap
– Metallic
• Metal atoms bonded to
several other atoms
• “Sea of electrons”
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Ionic Bonding
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Formation of Cations
Metals have LOW electronegativity and
LOW ionization energy so they will LOSE
electrons to form cations, positive ions.
The electron configuration of the sodium ion is the same as that of a
neon atom.
Formation of Anions
Non-metals have HIGH electronegativity and
HIGH ionization energy so they will GAIN
electrons to form anions, negative ions.
Both a chloride ion and the argon atom have an octet of electrons in their
highest occupied energy levels.
Forming Ions
• Cations (LOSE ELECTRONS) are always smaller than
the original atoms.
• Anions (GAIN ELECTRONS) are always larger than
the original atoms.
Predicting Ionic Charges
Group 1A: Lose 1 electron to form 1+ ions
H1+ Li1+
Na1+
K1+ Rb1+
Predicting Ionic Charges
Group 2A: Loses 2 electrons to form 2+ ions
Be2+ Mg2+ Ca2+ Sr2+ Ba2+
Predicting Ionic Charges
B3+
Al3+
Ga3+
Group 3A: Loses 3
electrons to form
3+ ions
Predicting Ionic Charges
Neither! Group 4A
Group 4A: Do they
elements rarely form ions lose 4 electrons or
EXCEPTION: Sn and Pb!! Treat like
transition metals
gain 4 electrons?
Predicting Ionic Charges
N3-
Nitride
P3-
Phosphide
As3- Arsenide
Group 5A: Gains 3
electrons to form
3- ions
Predicting Ionic Charges
O2-
Oxide
S2-
Sulfide
Se2- Selenide
Group 6A: Gains 2
electrons to form
2- ions
Predicting Ionic Charges
F1- Fluoride
Cl1- Chloride
Group 7A: Gains
Br1- Bromide 1 electron to form
I1- Iodide
1- ions
Predicting Ionic Charges
Group 8A: Stable
noble gases do not
form ions!
Predicting Ionic Charges
Many transition elements have more than one
possible charge. Also Pb and Sn (Group 4A)
2+
Iron
(II)
=
Fe
Use Roman numerals to
3+
Iron
(III)
=
Fe
show ion charges
Transition metals lose
electrons from s and d
sublevels!
Transition Metal Ions
Transition metals (and Pb & Sn) will lose electrons
from the s sublevel first and then from the d
sublevel.
Example: Cobalt forms Co2+ or Co3+
The electron configuration of a neutral cobalt atom is
written as follows.
Co: [Ar] 4s2 3d7
When forming ions, it will first lose from the s sublevel:
Co2+: [Ar] 3d7
And since the 3d orbital is so close to the s orbital, it will
then lose from the d sublevel:
Co3+: [Ar] 3d6
Ionic Bonding
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Formation of Ionic Compounds
– Ionic Bonds
– The electrostatic forces that hold ions together
in ionic compounds are called ionic bonds.
– Sodium loses 1 electron;
chlorine gains 1 electron
Writing Ionic Compound Formulas
Example: Aluminum sulfide
1. Write the symbols for the cation and
anion, including CHARGES!
2. Check to see if charges are
balanced.
3. Balance charges , if necessary, using
subscripts. Use the criss-cross method to
balance subscripts.
Al3+2 S2-3
Now balanced.
Not balanced!
= Al2S3
2 x +3 = +6
3 x -2 = -6
Overall charge = 0
Formation of Ionic Compounds
• Ionic compounds are arranged in a
3-D pattern = CRYSTAL LATTICE
This structure maximizes the attractive forces among
cations and anions while minimizing the repulsive forces.
Strength of Ionic Compounds
Lattice energy: the energy required to
separate the ions in a crystal lattice.
• Use Coulomb’s Law to describe the attraction between
cations and anions.
Stronger attraction if:
• Larger charges
• Smaller ions
Strength of Ionic Compounds
Coulomb’s Law
|𝑞1 𝑞2 |
E
𝑟
Where:
E = energy of attraction between charged particles
=> LATTICE ENERGY
q1 = charge of first particle (cation)
q2 = charge of second particle (anion)
r = distance between charged particles (estimated by
period number)
Strength of Ionic Compounds
E
|𝑞1 𝑞2 |

𝑟
• Which compound will have the
strongest lattice energy, LiCl or
NaCl?
– LiCl: E  |(-1)(+1)|/ 2
• Li + valence electrons in energy level
1, Cl - valence electrons in energy
level 3. Estimate r: (3 + 1)/2 = 2
Strength of Ionic Compounds (cont’d)
E
|𝑞1 𝑞2 |

𝑟
• Which compound will have the
strongest lattice energy, LiCl or NaCl?
– NaCl: E  |(-1)(+1)|/ 2.5
• Na+ valence electrons in energy level 2,
Cl - valence electrons in energy level 3.
Estimate r: (3 + 2)/2 = 2.5
– LiCl has the higher energy of
attraction between ions, therefore
has the highest lattice energy.
PRACTICE
E
|𝑞1 𝑞2 |

𝑟
Arrange the following ionic compounds in order of increasing
lattice energy: NaF, CsI, and CaO.
CsI < NaF < CaO
q1 = 1, q2 = -1,
both have the electron configuration of Ne
(valence shell in energy level 2)
E  1/2
Cs+ and I- q1 = 1, q2 = -1,
both have the electron configuration of Xe
(valence shell in energy level 5)
E  1/5
Ca2+ and S2- q1 = 2, q2 = -2,
both have the electron configuration of Ar
(valence shell in energy level 3)
E  4/3
Na+ and F-
PRACTICE
E
|𝑞1 𝑞2 |

𝑟
Arrange the following ionic compounds in order of increasing
lattice energy: KF, CsCl
K+ and F-
CsCl < KF
q1 = 1, q2 = -1,
K+ => argon, F- => neon
(valence shell in energy level (2+3)/2 = 2.5)
E  1/2.5
Cs+ and Cl- q1 = 1, q2 = -1,
Cs+ => xenon, Cl- => argon
(valence shell in energy level (5+3)/2 = 4)
E  1/4
Covalent Bonding
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Covalent Bonding
• In covalent bonds atoms share
electrons.
• Attractions between electrons
and nuclei are stronger than
the:
– Repulsions between electrons &
– Repulsions between nuclei
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Covalent Bonding
• Covalent bonds form to achieve the noble gas
configuration for each atom.
• Compounds with covalent bonds are called
MOLECULES.
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Covalent Bonding
• A covalent bond forms when two halffilled orbitals overlap.
• Hydrogen only uses the 1s orbital.
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Covalent Bonding
• Polyatomic ions are molecules with a
charge.
– Examples: NH4+
CO32-
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Multiple Covalent Bonds
Some compounds must share more than two
electrons to meet the octet rule.
Sharing 2 electrons
Sharing 4 electrons (2 pairs)
Sharing 6 electrons (3 pairs)
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Covalent Bond Length
Distances between centers of bonded atoms are
called bond lengths.
Bond
# of
electrons
Bond
Length
Bond
Strength
Single
2
Longest
Weakest
Double
4
Triple
6
Shortest
Strongest
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Bond Polarity
The bonding pairs of electrons in covalent
bonds are pulled by the nuclei.
Electronegativity
• Electronegativity is
the ability of atoms
in a molecule to
attract electrons to
themselves.
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Polarity
Polar covalent bond:
• between 2 nonmetal atoms with the
different electronegativity values
-
• bonding electrons are shared
unequally
• the atom with the higher electronegativity
pulls more strongly and has a partial
negative charge
• the atom with the lower electronegativity
pulls less strongly and has a partial positive
charge
+
Polar Covalent Bonds
The greater the
difference in
electronegativity,
the more polar is
the bond.
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Organic Chemistry
• The chemistry of carbon compounds
• Carbon:
• Can form covalent bonds with 4 elements
• Can form long chain molecules
• Is important in biochemistry (DNA, amino acids,
etc), Energy (gasoline, diesel), Plastics
(styrofoam, nylon).
•Alkanes
•
Hydrocarbons that contain only SINGLE
BONDS are ALKANES.
First Ten Alkanes
Formula Name
Formula Name
CH4
Methane
C6H14
Hexane
C2H6
Ethane
C7H16
Heptane
C3H8
Propane
C8H18
Octane
C4H10
Butane
C9H20
Nonane
C5H12
Pentane
C10H22
Decane
Alkane = CnH2n+2
Nomenclature of Alkanes
The first part of the names above correspond to
the number of carbons
(meth- = 1, eth- = 2, prop- = 3, but- = 4, etc. ).
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Organic Chemistry and Hydrocarbons
Formulas and Models for Methane and Ethane
Ball-and-stick model
Space-filling model
ALKENES
• Alkenes are hydrocarbons that contain one or
more carbon-carbon double covalent bonds.
• - Names end in –ene (or -ylene).
ALKYNES
• Alkynes are hydrocarbons that contain one or more
carbon-carbon triple covalent bonds.
• - Names end in –yne.
• Ethyne (also known as acetylene)
Alkynes
•The triple bond restricts rotation in an ethyne
molecule, which has a linear shape.
Functional Groups
–An atom or group of atoms that can take the place
of a hydrogen atom is called a functional group.
• If –OH replaces –H, the compound is an ALCOHOL.
• Alcohol names end in –ol.
Alcohols
• Ethanol (ethyl alcohol) is a common
component of many household products.
• Methanol is used as a fuel.
• Propanol is used as a fuel or cleaning fluid.
23.1
Functional
Groups
Halogen Functional Group
– A halocarbon is a hydrocarbon with a
halogen functional group.
Trichlorofluoromethane
Acetate Ion and Acetic Acid
Acetate ion: CH3COO-
Acetic Acid: CH3COOH
REVIEW:
•
Alkanes have which types of covalent bonds?
•
•
Single Covalent Bonds
Alkenes have which types of covalent bonds?
•
•
Double Covalent Bonds
Alkynes have which types of covalent bonds?
•
Triple Covalent Bonds