Download single covalent bond

Regents Chemistry
U10 L01
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What is a covalent bond?
Ionic Bonds involve a force of attraction that develops
through…
ELECTRON TRANSFER
In covalent bond formation the bond is formed by
ELECTRON SHARING
Both lead to the formation of the octet. However, The
force of attraction in Covalent compounds involves each
atom donating an electron to form a shared pair.
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Covalent Bonds
Many of the compounds we encounter in our daily
Lives are covalently bonded compounds
- Antibiotics
- Food
- Plants
- Plastics
ampicillin
- Clothing (Natural & Synthetic)
- Biochemicals
- What we breath and what we are
- And so many other things its impossible to
list them all!
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Molecular Bonds
Covalent Bonds fall into several sub-categories:
Non-polar Covalent
Polar Covalent
Coordinate Covalent
Network Covalent
We’ll start our discussion with non-polar covalent
bonds
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Formation of a non-polar Covalent Bond
(DEN < 0.4)
2 hydrogen Atoms
Approach each other
1s orbitals overlap
Each atom shares its
Electron with the
Other atom but…
Each atom thinks the shared electrons are theirs alone!
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This sharing of electrons creates a new bond
Between the atoms.
Covalent Bond
Electron density is concentrated in the region between
The atoms.
When 2 atoms approach the pt. of maximum attraction
a SINGLE COVALENT BOND forms
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If electron density is equally shared across both atoms
One side of the molecule has no more electron density
than the other side so no “poles “ develop
Non-polar
This type of bond is called…
Non-polar covalent
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Electronegativity differences
Recall that bonds formed by atoms with electronegativity
differences are greater than 1.7 are said to be IONIC
2 atoms with an electronegativity difference that is less
than 1.7 will form a COVALENT bond
When 2 atoms have an EN difference that is really low,
Less than or equal to 0.4 these bonds are said to be…
Non-Polar Covalent
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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
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Electronegativity differences
Between 0.4 and 1.7 there is a large number of
Compounds having bonds known as
Polar Covalent
For example H2O  3.4 - 2.1 = 1.3
We’ll talk more about Polar compounds later.
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Multiple atom electron sharing
Unshared electron pairs
All atoms now have an octet
In water, each hydrogen shares 1 electron with oxygen
Since oxygen initially has 6 electrons it has 2 pairs
Of electrons that remain unshared
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Unshared electron pairs are called LONE PAIRS
Shared electron pairs are called SHARED PAIRS or
BONDING PAIRS
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Nitrogen has a non-bonding pair of electrons
But Methane has no non-bonding pairs
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Depicting bonds
The most common way to depict bonds is not by
Lewis dot structures.
Instead, a line is drawn for each pair of shared
electrons
=
:
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How many bonding pairs and
Lone pairs are there in CH4
CH4
METHANE
Carbons S and P orbitals
Overlap with Hydrogen’s
S orbital to form a
Hybrid orbital known as a
Sigma bond. Its shape is
Unique – the tetrahedron
H
C
H
4 sigma bonds
(4 single covalent bonds) H
H
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Lewis dot structure
Lone pairs are not
Connected to the
Parent ion with a
line.
The electrons are
indicated using 2 “dots”
Cl
** Phosphorus’ lone pair
P
How would you draw the
Cl
Water molecule?
Cl
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Multiple bonds
So far we have looked at atoms sharing one pair of
Electrons to form a single covalent bond
It is however possible for atoms to share more than
a single pair of electrons
Oxygen (O2), for example, does this. Let’s see how.
Oxygen: 6e17
Multiple bonds
Oxygen’s oxidation number is -2
This means it has 6 electrons in it’s valence shell
To achieve the octet it needs 8 . So how does it do this?
1. A pair of
Electrons from
oxygen #1are shared
2. Oxygen #2 then
Shares one of its
Pair of electrons to
Complete the octet
#1
#2
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The sharing of 2 pairs of electrons is known as a
DOUBLE BOND. They can be formed by Molecules
having other than just two of the same atoms (like O2 )
Formaldehyde is an example
Propene is another.
H
H
H
Do the atoms in these molecules
have an Octet?
Some compounds may even
have several double bonds.
H
..
C = O:
C=C
H
H
..
:O = C = O:
Carbon Dioxide
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Triple Bonds
Nitrogen is an example of a compound that is formed
By sharing three pairs of electrons.
This is called a TRIPLE BOND
How many
Electrons does
Each atom have?
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Triple bonds
Another example of a Triple Bond is acetylene
H-C:::C-H
Electrons
from carbon 1
Oxy-acetylene torch
H-C
Electrons
From carbon 2
C-H
Acetylene
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Bond Energy
The strength of a Chemical Bond
Energy required to break a chemical bond
Measured in kJ/mole
A large bond dissociation energy corresponds to a
strong covalent bond.
Covalent Bond Strength: Triple > Double > Single
Bond Dissociation Energy
The energy necessary
to break
A bond in a given
Compound varies.
Different kinds of
Bonds take different
Energies to break
them apart.
Bond length
Bond Strength
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Bond Energies
Covalent vs. Ionic Properties
PROPERTY
IONIC COMPOUND
COVALENT COMPOUND
Simplest
Component
Formula Unit
Anion & Cation
Single Molecule
Structure
Crystalline
Amorphous solids (not
Crystalline) can also be
gas/liquid
Hardness
Hard
Solids relatively soft
Workability
Shatters if worked
Solids easily break apart
Electrical
Conductivity
Good Conductor ONLY if
molten or in solution
Non-conductors even if
molten
Melting Point
High (NaCl – 801 deg C)
Low
Boiling Point
High (NaCl – 1413 deg C)
Low
Ease of Phase
Change
Difficult – Low VP / High MP
& BP’s / High Hf
Easy – High vapor pressure
Solubility in
Water
Soluble – Covers range from
very soluble to very slightly
soluble
NaCl = 37.5g/100g water
Non-polar: insoluable
Polar: Soluble to slightly
soluble
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