Chem 1
Covalent bonds
Chapter 6: Chemical bonding
Valence electrons:
Kernal:
Chemical bond: mutual electrical attraction between nuclei and valence electrons of different
atoms. This binds the atoms together to form a compound.
Two basic bond types: Ionic- transfer of one or more e to form cations and anions.
Covalent: sharing electron pairs between two atoms
Ionic is stronger than covalent. (high mp)
Ionic occurs between atoms that are from opposite sides of the chart (M-NM)
Covalent bonds are divided into two types-non polar covalent = e pair is shared equally between
two atoms (weak bond – low mp)
Polar covalent bond e pair is shared unequally, the e-s spend more time around the more EN atom.
This causes an uneven distribution of charge.
Several other types of bonds will be discussed later
Electronegativity is used to determine bond type.
When two atoms bond, determine the bond type by subtracting the EN values from each other and
using the number line on side 2 of the chart to determine bond type.
Number line breaks 0.0-0.3 = npc, 0.4-1.6 = pc and 1.7- ? = I
Example:
NaI
CO2
FeO
Chemical Bonding
Covalent Bonding forms a molecule. It is a group of covalently bonded atoms that are neutral.
A chemical formula is generic-it shows the relative # of atoms in a compound (subscript)
Some atoms have the capability to bond with themselves. They are more stable-lower potential
energy.
These are called diatomic molecules. H-H, more stable because the outer level is completed and
stable. O=O
In any covalent compound, each nuclei repel one another, the e also repel one another.
The attraction between a nucleus and the other atoms electrons overcomes this repulsion.
Each bond has a bond length: distance between the bonded atom nuclei
Each bond has a bond energy: E required to break the chemical bond (or released when the bond
forms) kJ/mole
Some atoms have the ability to form multiple bonds
N-N (163 kJ), N=N (418) kJ, N triple bond N (945 kJ)
Double bonds involve the sharing of 2 electron pairs (4 electrons)
Triple bonds involve the sharing of 3 electron pairs (6 electrons)
These bonds are shorter than single bonds and have a larger bond energy-they do not break easily.
When you are making Lewis structures (electron dot), more than one structure may be needed.
The term for morethan one structure for the same compound is called resonance.
This uses more than one structure to illustrate properties. O3 (ozone)
Often a covalent compound will form a network solid. The molecules inter-bond together so that
an individual molecule does not exist. This usually raises mp
Symmetry also enters covalent molecules. If bonds are distributed equally and the same, the
molecule is nonpolar.
If the distribution of the bonds is not symmetrical, the molecule is polar.