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Double Bond : 2 pairs of electrons are shared
 Often occurs in C and O
 Stronger than single bonds, but not twice as
strong
O2
Intro. Triple bond with N2
Triple Bond: 3 pairs of electrons are shared
 Often occurs in N, O and C
 Stronger than single and double bonds
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Rules For Drawing Electron Dot Diagrams
For Covalent Molecules
1. Decide on the central atom:
 Usually it is listed first in the formula
 Usually it is the atom with the lowest
Electronegativity
 Hydrogen is never the central atom (it only forms 1
bond)
2. Arrange the rest of the atoms around the central atom
3. Count the total number of valence electrons of all atoms
4. Place one pair of electrons between each bonded atom
5. Use remaining electrons around the terminal atoms to
form stable octets (except H which needs only two)
6. If there are any extra electrons, add them to the central
atom
7. If the central atom has fewer that 8 electrons; form
multiple bonds (double and triple bonds)
Hints:
 If both hydrogen and oxygen are present, bond oxygen to
the central atom and then bond hydrogen to the oxygen.
 If more than one carbon atom is present, they will bond
to each: C-C-C
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Electronegativity: Relative attraction an atom has for a shared
electron. Ranges from 0.7 (F) to 3.98 (Fr)
Ionic bonds are bonds where the difference of attraction
between the two atoms is so significant that the electron is
transferred from one atom to the other creating ions.
NaCl dot model
Nonpolar Covalent Bonds are bonds where there is equal
sharing of electrons between atoms.
e.g. Cl2
N2O
Cl2 dot model
O-N-N
Cl - Cl
ΔEn = 0
En for O = 3.44
En for N = -3.04
ΔEn =
.40
A small difference in electronegativity (ΔEn) results in a
compound that has little attraction between molecules.
Consequently, the substance has low melting and boiling points
o CO2 boils at -78 ºC
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0.0
0.4
Non-polar
Covalent
1.67
3.28
Polar
Ionic
Rules For Determining Polarity of Bonds and Molecules
1. Ionic compounds have electronegativity differences of
1.67 or greater.
ΔEn > 1.67
2. Non-polar covalent bonds have electronegativity
differences less that 0.4
Δ En < 0.4
3. Polar covalent bonds have electronegativity differences
between 0.4 and 1.67
0.4 < Δ En < 1.67
Percent Ionic Character: Calculated by using the difference
in electronegativity and the chart on your periodic table.
Indicates to what degree a bond is ionic or covalent.
e.g. NaCl
Δ En = 2.23
Percent Ionic Character = 71%
Therefore: Percent Covalent Character = 29%
More examples
Polar molecules must have two distinctly differently charged
ends (one positive and one negative) All polar molecules must
contain polar bonds, however, some molecules with polar
bonds are not polar molecules
Polar molecules are also known as dipoles
(e.g. HCl vs. CO2). Dot models
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