Download non-polar bond

Mr. Shields
Regents Chemistry
U10 L02
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Bond vs. Electronegativity Differences
We know that if the EN difference between 2 atoms in
a bond is less than 1.7 then the bond is covalent
C
covalent
H
EN = 0.5
The COVALENT range between 0 & 1.7 can also be
Further Segmented:
If the difference is ≤0.5 the bond is NON-POLAR
If the difference is 0.6 – 1.7 the bond is said to be POLAR
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Least Ionic Most covalent
Most Ionic –
Least covalent
Molecules with differences
0.5 or less are said to be
Non-polar Covalent
3.2
2.1
Ionic
0.5
Polar Covalent Region
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Electron cloud
Non-polar covalent
A hydrogen molecule forms a covalent bond in
Which the electrons are equally shared by both
atoms
This is the basis of a non-polar bond
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Polar Bond
Distorted
Electron cloud
When one atom in a bond is much more electronegative
Than the other it pulls electron density towards it
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A Polar Covalent
Compound
Br
2.1
-
3.0
= 0.9
The atom that pulls electron density towards it more
strongly becomes partially negative while the other
atom becomes partially positive
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Polarity of Water
The electronegativity of O = 3.5
The electronegativity of H = 2.1
The difference is 1.4; the O-H bond is Polar covalent
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Water
Water is polar because electron density is pulled more
Strongly towards the Oxygen atom than the
Hydrogen atom.
This makes Oxygen
Partially negative
And the less
Electronegative H
Partially positive so…
There are 2 POLAR Covalent Bonds formed
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Bond Polarity vs. Molecular polarity
If two atoms form a polar bond you might assume
the molecule is polar.
However this is not always the case! Let’s see why…
Recall that a polar bond
Must have 2 ends with
Opposite charge.
Let’s look at the water
Molecule first…
Negative end
Positive end
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Polarity vs. Symmetry
Water is polar due to 2 effects:
Polar bonds
Polar molecule
1) It has polar covalent O-H bonds
2) The molecule has a
BENT geometric shape.
The bent shape gives it an
Asymmetry that allows
two opposite polar ends
To develop.
Negative end
Positive end
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Carbon Dioxide
Now let’s look at Carbon Dioxide.
The 2 C = O bonds in CO2 are in fact polar covalent,
Just like water (what’s the electronegativity difference?)
Because the electronegativity difference is >0.5 we
expect the CO2 molecule to be polar …
But it isn’t. How Come ????
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CO2 is actually a linear
molecule.
As a linear molecule it
Has a symmetry through
Carbon.
That means that the ends
Of the molecule are BOTH
Negative and there is NO
Defined Positive END
It’s this symmetry that makes
The molecule NON-POLAR
Instead of POLAR.
VECTORS CANCEL
..
..
:O = C = O:
-
+
-
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Other examples of symmetry
related non-Polar molecules
What is the electronegativity difference between C
and Cl?
Would it form a polar or non-polar Bond?
Based on this is CCl4 a polar or non-polar
Molecule (it has 4 C-Cl bonds)?
CCl4 is in fact a non-polar molecule. Let’s see why
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CCl4 has the shape of a Tetrahedron (Like many C-H
Containing Compounds such as methane)
H
CH4
H
C
H
Methane
ClCCl4
H
Cl-
C+
Cl-
Carbontetrachloride
(w/partial charges)
Cl-
Notice the symmetry of these molecules. When each
Is rotated is looks the same from any angle.
Due to this symmetry there is no negative end, no
Positive end and the molecule is NON-POLAR.
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Summary
1. Molecules containing only non-polar bonds are
always Non-polar
examples:
O2, N2, I2, CH4
2. Molecules containing polar bonds with symmetrical
charge distributions are Non-polar
examples:
CO2, CCl4
3. Molecules containing polar bonds with asymmetrical
charge distributions are Polar
examples:
HF, H2O, NH3, CH3Cl
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Coordinate Covalent Bonds
Recall…
A covalent bond is formed between two atoms,
EACH donating 1 electron to form a shared pair.
When one of the two atoms donates BOTH electrons
To form the shared pair the bond is called
COORDINATE COVALENT.
This type of bond is found in many POLYATOMIC
IONS (but not exclusively)
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Coordinate Covalent Bonds
Let’s look at some example of molecules with coordinate
Covalent bonds and how they’re formed?
Oxygen contributes electron pair
Nitrogen contributes electron pair
Carbon Monoxide
Oxygen contributes electron pair
H
H
+
O:
H
Hydronium ion
Ammonium ion
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Formation of a Coordinate Covalent bond
A polyatomic:
The hydronium ion
Std Polar covalent bonds
In the water molecule
Electron pair
Donated solely
By Oxygen
The added
Proton to the
Water molecule
leads to
The positive
charge
H20 + H+  H3O+
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Problem:
1. Ammonium Chloride is an ionic compound. Why?
NH4Cl
2. Draw the Lewis dot structure for this compound
3. What kind of covalent bonds are present?
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Network Solids
Some atoms are able to form multiple repeating
covalent bonds with themselves.
- for example: carbon
Certain other atoms can also form multiple repeating
covalent bonds with another atom
- for example: Si and O or B and N,
The result is a three dimensional structure known as a
NETWORK SOLID
Let’s look at some examples.
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Diamond is an example of a network solid
A highly interconnected carbon
Covalent Structure consisting
of Hexagonal rings
1 carbon
Bonded to
4 others
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Allotropes
- Carbon can covalently bond with itself in several
different geometric structures
- Different combinations or geometric structures of the
same element or molecule are known as ALLOTROPES
- Examples of allotropes:
- Diamond, Graphite, Coal, buckyballs
- O2, O3  These are are allotopes but
not network solids
- Allotropes have different physical and chemical
properties.
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Graphite is an allotrope of diamond and like diamond
it consists of connected hexangonal rings. It is also a
network solid
Unlike diamond however, these rings form layers that
are not connected and can slide across one another.
It’s this structure that gives
graphite its lubricating quality &
Electrical
Conductivity
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4 Other Examples of Network
Solids
BN
A Lubricant like
Graphite
MP 2967 C
SiO2
Quartz
MP 1650 C
Si3N4
SiC
MP
1900 C
Extremely
Hard
MP 2700 C
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Network solids
PROPERTIES:
 Extraordinarily high melting points
 Very hard
 Not soluble in polar or non-polar liquids
 Non conductors of electricity in either solid
or liquid state
 Notable Exception: Graphite does conduct
electricity!
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