BondingChapter 12
What is a Bond? A force that holds atoms together. Why? We will look at it in terms of energy. Bond energy the energy required to
break a bond. Why are compounds formed?
Because it gives the system the lowest energy.
0
Ener
gy
Internuclear Distance
0
Ener
gy
Internuclear Distance
0
Ener
gy
Internuclear Distance
0
Ener
gy
Internuclear Distance
0
Ener
gy
Internuclear Distance
Bond Length
0
Ener
gy
Internuclear Distance
Bond Energy
Ionic Bonding An atom with a low ionization energy
reacts with an atom with high electron affinity.
The electron moves. Opposite charges hold the atoms
together.
What about covalent compounds?
The electrons in each atom are attracted to the nucleus of the other.
The electrons and nuclei repel each other,
They reach a distance with the lowest possible energy.
The distance between is the bond length.
Covalent Bonding Electrons are shared by atoms. These are two extremes. In between are polar covalent bonds. The electrons are not shared evenly. One end is slightly positive, the
other negative. Indicated using small delta d.
The Relationship Between
Electronegativity and Bond Type
Dipole Moments A molecule with a center of negative
charge and a center of positive charge is dipolar (two poles),
or has a dipole moment. Center of charge doesn’t have to be
on an atom. Will line up in the presence of an
electric field.
H - Fd+ d-
H - Fd+ d-
H - Fd+
d-H - Fd+d-
H - F
d+d-
H - F d+d-
H - Fd+d-
H - Fd+
d-
H - F d+d-
H - Fd+ d-
H - Fd+
d-H - Fd+d-
H - F
d+d-
H - F d+d-
H - Fd+d-
H - Fd+
d-
H - F d+d-
+-
H - Fd+ d-
H - Fd+ d-
H - Fd+ d- H - F
d+ d-
H - Fd+ d-
H - Fd+ d-
H - Fd+ d- H - F
d+ d-
- +
An Electrostatic Potential Map of HF
The Charge Distribution in the Water Molecule
The Carbon Dioxide Molecule
Size of Isoelectronic ions Iso - same Iso electronic ions have the same #
of electrons Al+3 Mg+2 Na+1 Ne F-1 O-2 and N-3 All have 10 electrons. All have the configuration 1s22s22p6
Size of Isoelectronic ions Positive ions have more protons so
they are smaller.
Al+3
Mg+2
Na+1Ne F-1 O-2 N-3
Forming Ionic Compounds
Lattice energy - the energy associated with making a solid ionic compound from its gaseous ions.
M+(g) + X-(g) ® MX(s) metal nonmetal ionic compound This is the energy that “pays” for
making ionic compounds.
The Structure of Lithium Fluoride
Localized Electron Model
Simple model, easily applied. A molecule is composed of atoms
that are bound together by sharing pairs of electrons using the atomic orbitals of the bound atoms.
Three Parts1) Valence electrons using Lewis
structures2) Prediction of geometry using
VSEPR3) Description of the types of orbitals
Exceptions to the octet rule
BH3 B wants 6
Be and B often do not achieve octet Have less than an octet, for electron
deficient molecules. SF6
Third row and larger elements can exceed the octet
Use 3d orbitals? I3
-
Exceptions to the octet When we must exceed the octet,
extra electrons go on central atom. ClF3
XeO3
ICl4-
Resonance Sometimes there is more than one valid
structure for an molecule or ion. NO3
-
Use double arrows to indicate it is the “average” of the structures.
It doesn’t switch between them; the electrons are delocalized
NO2-
Top Related