Covalent Bonding

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Chemical Bonding
Part 1
Covalent Bonding
Types of Chemical Bonds
• Covalent Bonds
– Single
– Double
– Triple
-- Polar
-- Non-Polar
• Ionic Bonds
• Metallic Bonds
• Other “Bonds”
– Inter-Molecular Forces
first…
A PREVIEW & SUMMMARY
Ionic Bonds
of the 3 main types of bond:
while keeping in mind:
Atoms are unhappy  if their outer
energy level is not full!!
Atoms only bond with other atoms in
order to fill their outer energy level.
Covalent Bonds
A covalent bond exists when two electrons
are shared by non-metallic atoms.
An ionic bond is the attraction
between an anion and a cation,
which form after an electron is transferred
from a metal to a non-metal
Metallic Bonding
Takes place in a
“SEA” OF MOBILE VALENCE ELECTRONS
1
Covalent Bonds:
…are formed when
two atoms share a pair of electrons.
…always form between
two non-metal atoms.
…always form between atoms with
similar electronegativity values.
Covalent Bonding Example
Time for an example:
6+
-
-
Vacancies
Covalent Bonding Example
Time for an example:
How many
electrons
does carbon
need to be
happy?
4 electrons!
6+
-
-
-
Carbon
Covalent Bonding Example
Remember, H has 1 e-(electron), and 1
p+(proton).
-
1+
Carbon
Covalent Bonding Example
Covalent Bonding Example
Remember, H has 1 e-(electron), and 1
p+(proton).
Remember, H has 1 e-(electron), and 1
p+(proton).
Is H
happy?
-
1+
How many
vacancies
does H have?
-
1+
Nope!
1!!!
2
Covalent Bonding Example
Covalent Bonding Example
Let’s see how this looks…
OK, time for the big moment:
If C has 4 vacancies, and H has 1,
how many H can bond with C?
-
-
4!!!
Hydrogen
Carbon
Covalent Bonding Example
Covalent Bonding Example
Let’s see how this looks…
Now we need to add our other H’s…
-
-
Hydrogen
-
Carbon bonds
with 4 hydrogens
to form a
methane
molecule:
-
- -
-
-
-
Carbon
Single, Double and Triple Bonds:
a SINGLE covalent bond is formed
by TWO electrons:
Single, Double and Triple
Bonds
a DOUBLE covalent bond is formed
by FOUR electrons:
3
Single, Double and Triple
Bonds
A water molecule contains
two, single covalent bonds:
a TRIPLE covalent bond is formed
by SIX electrons:
C
Each
bond
consists of
one pair of
electrons
being
shared.
C
Other Examples of Covalent
Bonding:
Diatomic Molecules
Other Examples of Covalent
Bonding:
Diatomic Molecules
Hydrogen(H2)
Whenever an element bonds with itself, a
“diatomic molecule” is created.
Many important molecules are covalently
bonded diatomic molecules, for example
H2, O2, N2, Cl2 (atmospheric & other gases)
Other Examples of Covalent
Bonding:
Diatomic Molecules:
Hydrogen(H2)
two electrons form a
covalent bond
two H atoms held together
by a single covalent bond
Covalent Bonding
Oxygen(O2)
Double
Bond
4
Naming Covalent Compounds
Covalent bonding
• Results from the sharing of a pair
of valence electrons
• Between non-metals only (and
Hydrogen)
• Single, Double or Triple Bonds
• Unequal sharing is called a
polar covalent bond (more on
this later)
some stuff you already know:
_______________________
CO2
Carbon Dioxde
_______________________
SO2
____
Sulfur Dioxide
NF3
____
MonoDiTriTetraPenta-
6
7
8
9
10
HexaHeptaOctaNonaDeca-
Examples:
Carbon Tetrachloride
CCl4 _______________________
Diphosphorous Pentoxide
P2O5 _______________________
N2O4
____
Dinitrogen Tetroxide
P4S10 Tetraphosphorous Decasulfide
____
Nitrogen Trifluoride
Rules for Naming
Covalent Compounds
Prefixes
used for covalent compounds:
1
2
3
4
5
Carbon Monoxide
CO
1. Name the first element
(the least electronegative is first)
(the furthest left on the periodic table.)
2. If there is more than one atom of that
element, add a prefix.
3. Name the next element & add a prefix.
(even if there is only one, add “mono-”)
4. Add the “-ide” suffix.
LEWIS DOT STRUCTURES
…are sketches of molecules or atoms
that show
valence electrons as dots
C
Carbon
4 valence e-
Na
Sodium
1 valence e-
F
Fluorine
7 valence e-
5
LEWIS DOT STRUCTURES
The Octet Rule
are helpful to show how valence electrons
are involved in bonding:
Remember: Atoms only bond in order to fill
their valence shell.
Two F atoms:
F
F
In the case of
Hydrogen, this means
having 2 valence
electrons. (duet rule)
One F molecule:
F
F
Single covalent bonds
are drawn as single lines
F
Remember: Single Covalent Bond = 2 electrons
Rules for Drawing
Lewis Structures
:
F
H
:
H
In the case of most other
non-metal elements this
means getting 8 valence
electrons (octet rule).
•
Use one pair of electrons to form a covalent
bond between outside atoms and the central
atom.
1. Calculate the total number of valence
electrons for each atom, and add them up.
•
Arrange the remaining electrons to complete
the octets of the outside atoms.
2. If there are more than two atoms, start with
central atom (usually the least electronegative
but never hydrogen).
•
If the central atom lacks an octet, then form
double or triple bonds instead. Make sure all
atoms have an octet, except Hydrogen, which
always has 1 bond.
Resonance structures
Sometimes more than one correct Lewis
structure can be drawn; especially if there are
double and triple bonds.
Example:
In such a case we call the various structures
resonance structures.
6
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