Polar Nonpolar Dipole
All have the word “pole” in it, meaning “a part of a system that has opposite positions”
Ex: North Pole and South Pole refers to opposite locations and magnetic fields on earth.
In chemistry Polar refers to oppositely charged sides of a molecule
Vocabulary
Main point- How bad do you want that item? In chemistry this is electronegativity.
Is sharing always equal?
We know the shortcuts for finding out the type of compound and bond formed.
Metal with non-metal = ? Metal with metal = ? Non-metal with non-metal = ?
This shortcut is really based on electronegativity (how much does one atom want the electrons of the other atom)
Electronegativity determines the bond type
Actual values for each atom on page 405
H=2.1 Cl = 3.0 F= 4.0 C= 2.5 Na=0.9
Electronegativity chart
Electronegativity difference
Type of Bond Example
0.0 – 0.4 Nonpolar covalent
H-H or C-H
>0.4-1.9 Polar covalent H-Cl or H-F
> 2.0 Ionic NaCl
When both atoms pull on the electrons equally, the electrons are shared equally.
This happens when both atoms are the same (H2, O2, N2, Cl2, F2, Br2, I2)
It also happens when both atoms have very similar electronegativity values
Ex: C-H, C-C
Nonpolar covalent bonds
When the two atoms pull on the electrons unequally.
The more electronegative atom will pull harder and acquire a slight negative charge
The less electronegative atom will pull less and acquire a slight positive charge
This is denoted by a delta (delta +, delta -)
Polar covalent bonds
A molecule with one side slightly positive and the other side slightly negative
HCl HF CO H20 NH3
Not polar: CH4 does not have any polar bonds CO2 even though it has polar bonds
Polar molecules
Same atoms on bond = non-polar bond C and H = non-polar bond Every other combination usually polar
Sure solution: Look up electronegativities on page 405 and compare to table on page 463
General Rule for identifying bonds as polar or nonpolar
HW: Fill out the table belowUse the charts on p.405 and p.463
Bonded atoms Difference in electronegativity
Polar or nonpolar covalent bond?
H - H 2.1 – 2.1 = 0 Non-polar
H - C
H - O
H - N
C – C
C - O
C - N
S - Cl
O - N
P - F
Br - Br
Likes dissolve likes is a phrase that tells you which molecules will mix and which will not.
Polar dissolves polar Nonpolar dissolves nonpolar Polar will not mix with nonpolar
Demonstrate with a bottle that has oil and water in it
Demonstrate with two beakers, one water, one oil, and 2 cubes of sugar in each one.
What does the term “likes dissolve likes” mean in regards to polarity?
Atoms bond to have complete outer orbitals When they get there, they stop bonding and
become the compound they become If only covalent bonds existed, each little
molecule would be completely independent and every molecular compound would be a ?
Gas! We would have no liquid!!! So there must be OTHER interactions taking place between molecules…
Intermolecular attractions
Van Der Waals Forces◦ 1) London Dispersion forces◦ 2) Dipole-dipole interactions
3) Hydrogen bonds-◦ The strongest of the intermolecular forces
The 3 weak intermolecular forces/attractions
The electrons of amolecule will shift to oneside, creating a temporary dipole. This dipole willcause the other moleculeto create a dipole as welland attraction will occur fora very short time. This occurs between nonpolar molecules
London Dispersion forces
The slightly positive part of one molecule will attract the slightly negative part of another molecule.
This occurs between two polar molecules.
Dipole-dipole forces
The strongest of the 3 intermolecular forces A hydrogen covalently bonded to N, O, or F
will be very electron deficient ( +)
It will become attracted to an unshared pair of a different molecule.
Hydrogen bonding
1) Non-polar vs polar◦ Polarity explains why water and oil do not mix!
Oil is non-polar, Water is polar◦ Polarity explains why water dissolves ionic
compounds!
Why does this matter?
2) Intermolecular forces◦ Explain why liquids and solids exist! ◦ Explains the melting and boiling points of
molecular compounds.◦ Hydrogen bonding explains why water has such
high surface tension! ◦ Helps DNA and proteins take the
shapes that they take!
Why does this matter?
21) You find the difference in electronegativity between the atoms.
<0.4 is nonpolar covalent 0.5-1.9 is polar covalent >2 is ionic
22) dispersion, dipole-dipole, hydrogen bond
23)CCl4 has polar bonds, but is not a polar molecule because of symmetry (it doesn’t have a (+) and (-) side.
24)HOOH, BrCl, HBr, H2O
26)shared bonding electrons, solubility ranges from high to low, exist as molecules
HW:
Polar bond – a covalent bond where electrons are shared unequally◦ The more electronegative atom is slightly negative◦ The less electronegative atom is slightly positive
Non-Polar bond –a covalent bond where electrons are shared equally ◦ Both atoms have similar or identical electronegativity
Dispersion – weak forces caused by the random motion of electrons◦ The only attractions non-polar molecules can have
Dipole-dipole – attractions between polar molecules◦ The slightly positive end of one molecule attracts the slightly negative
end of another
Hydrogen bond – an attraction where a hydrogen (that is bonded to an N, O, or F) is attracted to an unshared pair of electrons on another molecule.◦ The strongest intermolecular attraction of the three