Chemical Bonding

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Chemical Bonding

• Chapter 8 Sections 1 2

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• A chemical bond is a force of attraction between
  any two atoms in a compound.
• Bonding between atoms occurs because it creates a
  more stable arrangement for the atoms.

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Lewis Symbols Dot Diagrams

• Convenient way to show the valence electrons

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Three types of bonding

• Metallic bonding results from the attraction
  between metal atoms and the surrounding sea of
  electrons
• Ionic bonding results from the electrical
  attraction between large numbers of cations and
  anions
• Covalent bonding results from the sharing of
  electron pairs between two atoms

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Ionic Bonding

• Many atoms transfer electrons and other atoms
  accept electrons, creating cations (positive
  metal ions) and anions (negative nonmetal ions).
• The resulting ions are attracted to each other by
  electrostatic force.

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Ionic bonding between Na and Cl
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Covalent bonding

• In many cases electrons do not completely
  transfer from one atom to another.
• The electrons between atoms are shared.

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Covalent bonding between H2

• Hydrogens electron configuration is 1s1
• Because both H atoms need 1 more electron to
  become isoelectronic with He, it is unlikely that
  either will give up an electron.

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Covalent bonding between H2

• ?

1s
?
1s
They share the two electrons. H H ?
H H
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Types of Covalent Bonds

• When electrons are shared equally the bond is
  called a NONPOLAR covalent bond. (i.e. H2)
• Sometimes the electrons between two atoms are NOT
  shared equally. The bond created is called a
  POLAR covalent bond.
• . . . .
• H Cl ? HCl
• . . . .

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Polar Covalent Bonding

• An example of this would be HCl.

HCl molecule Hydrogen atom
? 1s
Ne ?? ?? ?? ? 3s
3p
Chlorine atom
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How to classify bond types

• Electronegativity measure of the ability of an
  atom to attract electrons in a chemical bond
• Each element on the periodic table is assigned an
  electronegativity value (see page 353) that
  ranges from 0.7 to 4.0.
• The difference in the electronegativity
  determines the bonding type (ionic, polar
  covalent, or nonpolar covalent).

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If the electronegativity difference is

• 1.7 and higher ionic
• 0.3 to 1.7 polar covalent
• 0.0 to 0.3 nonpolar covalent

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What if I get an electronegativity difference
that is 0.3 or 1.7?

• These cut-off numbers are guidelines.
• It is a gradual change not stair-step.

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Ionic Character

• As the electronegativity difference increases,
  the ionic character increases as well!

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Practice Problems

• What type of bond will occur between iodine and
  the following elements cesium, iron, and sulfur?

Bonding between I and Electronegativity difference Bond Type
Cesium
Iron
Sulfur
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Answers to problems
Bonding between I and Electronegativity difference Bond Type
Cesium 2.5 0.7 1.8 Ionic
Iron 2.5 1.8 0.7 Polar covalent
Sulfur 2.5 2.5 0.0 Nonpolar covalent
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Determine the type of bond between the following
pairs.
Bonding between Electronegativity difference Bond type
Li Cl
S O
Ca Br
P H
Si Cl
S Br
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Answers
Bonding between Electronegativity difference Bond type
Li Cl 3.0 1.0 2.0 Ionic
S O 3.5 2.5 1.0 Polar covalent
Ca Br 2.8 1.0 1.8 Ionic
P H 2.1 2.1 0.0 Nonpolar covalent
Si Cl 3.0 1.8 1.2 Polar covalent
S Br 2.8 2.5 0.3 Nonpolar covalent