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.

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Ener

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Internuclear Distance

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Internuclear Distance

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Internuclear Distance

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Internuclear Distance

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Internuclear Distance

Bond Length

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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-