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Chemical BondingChapter 4 Section 1
• 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.
Lewis Symbols – Dot Diagrams
• Convenient way to show the valence electrons
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
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.
Ionic bonding between Na and Cl
Sodium atom Chlorine atom 1s2 2s2 2p6 3s1 1s2 2s2 2p6 3s2 3p5 1s2 2s2 2p6 3s1 1s2 2s2 2p6 3s2 3p5 Sodium ion Na1+ Chlorine ion Cl1- 1s2 2s2 2p6 1s2 2s2 2p6 3s2 3p6
Covalent bonding
• In many cases electrons do not completely transfer from one atom to another.
• The electrons between atoms are shared.
Covalent bonding between H2
• Hydrogen’s 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.
• They share the two electrons.
H· + H · H : H
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: H:Cl:
. . . .
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 87) that ranges from 0.7 to 4.0.
• The difference in the electronegativity determines the bonding type (ionic, polar covalent, or nonpolar covalent).
If the electronegativity difference is:
1.7 and higher ionic
0.3 to 1.7 polar covalent
0.0 to 0.3 nonpolar covalent
Practice ProblemsWhat type of bond will occur between
iodine and the following elements: cesium, iron, and sulfur?
The electronegativities of each are:
Iodine 2.5
Cesium 0.7
Iron 1.8
Sulfur 2.5
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
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.
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
AnswersBonding 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