Chemistry 11
Chemical Bonding
Electronegativity – the tendency of an atom
to attract electrons from a neighbouring
atom.
Hey! I
find your
electrons
attractive!
Get
lost,
loser!
Electronegativity decreases as you move down each column.
Electronegativity increases as you move from left to right.
Valence Electrons – electrons in the
outermost occupied energy level. (s and p
electrons outside the core)
Valence electrons can be represented by
“dots” drawn around the atom.
Gilbert Newton Lewis
Invented “Electron-dot”
formulas or “Lewis
Structures”
I’m so tired of writing
all those useless inner
electrons, in the
Bohring models!
When the electronegativities of two atoms are
quite different from each other:
One atom loses an electron (or electrons)
The other atom gains an electron (or electrons)
This results in an Ionic
Bond.
Chemical Bonding (Choose Ionic Bonds)
crystal lattice viewer
NaCl
Crystal Lattice
Li
F
A Li Atom
An F Atom
+
Li
F
A Li+ Ion
An F- Ion
Be
F
An F Atom
F
An F Atom
A Be Atom
-
-
2+
F
Be
F
A Be2+ Ion
An F- Ion
An F- Ion
The melting points of some Ionic
Compounds are as follows:
NaF
KCl
LiCl
993 oC
770 oC
605 oC
These high melting points are
experimental evidence that Ionic Bonds
are VERY STRONG. (Hard to break just
by heating).
When Electronegativities of bonding atoms
are the same (as they are in diatomic
molecules) or close to the same, they
SHARE electrons.
Bonds formed when atoms share electrons
are called Covalent Bonds.
In diatomic molecules (like H2 or Cl2), the
electronegativities of both atoms are
exactly the same so electrons are shared
equally!
Covalent Bond animation
In Covalent bonds, electrons
are Shared
H
H
Covalent bonds in large networks
(Network Bonding) gives rise to
substances with very high melting points.
diamond structure
Diamonds are “forever”!
Some melting points of Network Solids:
Diamond (Carbon) 3550 oC
Silicon Carbide (SiC) 2700 oC
Boron Nitride (BN) 3000 oC
Covalent
bonds are
very
strong!
When electrons are shared unequally between two
atoms, the bond is called Polar Covalent. A type of
PC bond formed when “H” from one atom
attracts “O” or “N” from another atom is called
Hydrogen Bonding. polar covalent bonds
Hydrogen Bonding
in Water gives rise
to the structure of
ice when water
solidifies.
Hydrogen
bonds
between the
“bases” hold
the two
strands of
DNA
together.
Bonds within molecules that hold the atoms
of a molecule together are called
intramolecular bonds. They are strong
covalent bonds.
Covalent Bonds
The covalent
intramolecular
bond in I2 is
very strong.
I
I
I
I
I
I
I
I
I
I
I
I
There are weaker
intermolecular
forces which hold
covalent molecules
together in a
molecular solid.
A dipole is a partial separation of charge
which exists when one end of a molecule
has a slight positive charge and the other
end has a slight negative charge. Eg. A
water molecule has two dipoles.
The Greek letter d
“delta” means
“partial”
Just by pure chance, there are some times
when both electrons in helium are on the
same side. This forms temporary dipoles
ee-
e+2
e-
He
d-
+2
He
d+
d-
d+
The weak attractive forces between the
(+) side of one molecule and the (-) side
of another molecule are called London
Forces
The covalent
intramolecular
bond in I2 is
very strong.
I
I
I
I
I
I
I
I
I
I
I
I
There are weaker
intermolecular forces which
hold covalent molecules
together in a molecular solid.
These are called London
Forces. Since they are
relatively weak, Iodine has a
low melting point.
Lewis Structures (Electron-dot formulas)
for Ionic Compounds.
Remember, in an ionic compound, the
metal loses e-’s and the non-metal gains.
There is no sharing. Here is the e-dot
formula for sodium chloride (NaCl)
Na+
Cl
Here is the e-dot formula (Lewis Structure)
for the ionic compound MgF2 :
F
Mg2+
F
Notice, there is no sharing. The F atoms
took both valence e-’s from Mg, forming
ions which do not share electrons. The +
and – charges on the ions cause them to
attract each other.
Electron-dot Formulas (Lewis Structures)
for Covalent Compounds.
When atoms form covalent bonds, they
are trying to achieve stable noble gas
electron arrangements:
Hydrogen will share e-’s until it feels 2 e-’s
like Helium.
Other elements share e-’s to achieve what
is called a “Stable Octet” (8 valence e-’s)
Electron-dot formula for Methane (CH4)
H
H
C
H
Here is a Carbon
atom (4 val e-’s) and
four Hydrogen
atoms (1 val e- each)
H
Electron-dot formula for Methane (CH4)
H
H
C
H
Here is a Carbon
atom (4 val e-’s) and
four Hydrogen
atoms (1 val e- each)
H
Electron-dot formula for Methane (CH4)
H
H
C
H
Here is a Carbon
atom (4 val e-’s) and
four Hydrogen
atoms (1 val e- each)
H
Electron-dot formula for Methane (CH4)
H
H C H
H
Here is a Carbon
atom (4 val e-’s) and
four Hydrogen
atoms (1 val e- each)
Electron-dot formula for Methane (CH4)
H
H C H
H
Electron-dot formula for Methane (CH4)
H
H C H
H
Electron-dot formula for Methane (CH4)
H
Now they have
formed a stable
molecule. Each
C atom “feels”
like it has a
stable octet.
H C H
H
Electron-dot formula for Methane (CH4)
H
Now they have
formed a stable
molecule. Each
C atom “feels”
like it has a
stable octet.
H C H
H
Electron-dot formula for Methane (CH4)
H
Now they have
formed a stable
molecule. Each
C atom “feels”
like it has a
stable octet.
H C H
H
Electron-dot formula for Methane (CH4)
H
Now they have
formed a stable
molecule. Each
C atom “feels”
like it has a
stable octet.
H C H
H
Electron-dot formula for Methane (CH4)
H
Now they have
formed a stable
molecule. Each
C atom “feels”
like it has a
stable octet.
H C H
H
Electron-dot formula for Methane (CH4)
H
Now they have
formed a stable
molecule. Each
C atom “feels”
like it has a
stable octet.
H C H
H
Each H atom
“feels” like a
stable “He”
atom with 2e-s
Electron-dot formula for Methane (CH4)
H
Now they have
formed a stable
molecule. Each
C atom “feels”
like it has a
stable octet.
H C H
H
Each H atom
“feels” like a
stable “He”
atom with 2e-s
Electron-dot formula for Methane (CH4)
H
Now they have
formed a stable
molecule. Each
C atom “feels”
like it has a
stable octet.
H C H
H
Each H atom
“feels” like a
stable “He”
atom with 2e-s
Electron-dot formula for Ammonia (NH3)
H
N
Here is a Nitrogen
atom (5 val e-’s) and
three Hydrogen
atoms (1 val e- each)
H
H
Electron-dot formula for Ammonia (NH3)
H
Here is a Nitrogen
atom (5 val e-’s) and
three Hydrogen
atoms (1 val e- each)
N
H
H
Electron-dot formula for Ammonia (NH3)
H
N
H
Here is a Nitrogen
atom (5 val e-’s) and
three Hydrogen
atoms (1 val e- each)
H
Electron-dot formula for Ammonia (NH3)
H
N
H
Here is a Nitrogen
atom (5 val e-’s) and
three Hydrogen
atoms (1 val e- each)
H
Electron-dot formula for Ammonia (NH3)
H N H
H
Electron-dot formula for Ammonia (NH3)
H N H
H
Electron-dot formula for Ammonia (NH3)
“N” now
feels like it
has a stable
octet
H N H
H
Electron-dot formula for Ammonia (NH3)
“N” now
feels like it
has a stable
octet
H N H
H
Electron-dot formula for Ammonia (NH3)
“N” now
feels like it
has a stable
octet
H N
H
H
Electron-dot formula for Ammonia (NH3)
“N” now
feels like it
has a stable
octet
H N H
H
Electron-dot formula for Ammonia (NH3)
“N” now
feels like it
has a stable
octet
H N H
H
Electron-dot formula for Ammonia (NH3)
“N” now
feels like it
has a stable
octet
H N H
H
Electron-dot formula for Ammonia (NH3)
“N” now
feels like it
has a stable
octet
H N H
H
Each “H”
feels like it
has 2 e- like
Helium.
Electron-dot formula for Ammonia (NH3)
“N” now
feels like it
has a stable
octet
H N H
H
Each “H”
feels like it
has 2 e- like
Helium.
Electron-dot formula for Ammonia (NH3)
“N” now
feels like it
has a stable
octet
H N H
H
Each “H”
feels like it
has 2 e- like
Helium.
Electron-dot formula for Ammonia (NH3)
“N” now
feels like it
has a stable
octet
H N H
H
Each “H”
feels like it
has 2 e- like
Helium.
Electron-dot formula for Ammonia (NH3)
“N” now
feels like it
has a stable
octet
H N H
H
Each “H”
feels like it
has 2 e- like
Helium.
Electron-dot formula for Ammonia (NH3)
“N” now
feels like it
has a stable
octet
H N H
H
Each “H”
feels like it
has 2 e- like
Helium.
Electron-dot formula for Ammonia (NH3)
H N H
H
Each “H”
feels like it
has 2 e- like
Helium.
Electron-dot formula for Ammonia (NH3)
H N H
H
Electron-dot formula for Ammonia (NH3)
H N H
H
Electron-dot formula for Ammonia (NH3)
H N H
H
Electron-dot formula for Ammonia (NH3)
H N H
H
Electron-dot formula for Ammonia (NH3)
H N H
H
Electron-dot formula for Ammonia (NH3)
H N H
H
Electron-dot formula for Ammonia (NH3)
H N H
H
Electron-dot formula for Ammonia (NH3)
H N H
H
Electron-dot formula for Ammonia (NH3)
H N H
H
Electron-dot formula for Ammonia (NH3)
H N H
H
Electron-dot formula for Ammonia (NH3)
H N H
H
I’m so
HAPPY!
Write the electron-dot formula for CF4
Write the electron-dot formula for CF4
Because “F” is a
halogen, it has 7
valence e-s, so
you must show
all 7 red dots
around each
“F” atom!
F
F
C F
F
Write the electron-dot formula for H2S
Write the electron-dot formula for H2S
S H
H
The two H’s
MUST be at
right angles to
each other!!
Write the electron-dot formula for H2S
These are called “lone
pairs”. They must
also be at right angles
to each other when
the central atom is in
Group 16!
S H
H
Write the Electron-Dot Formula for SeF2
Write the Electron-Dot Formula for SeF2
Se F
F
Write the Electron-Dot Formula for SeF2
Se
F
F
Because Se is in
Group 16, the F
atoms MUST be at
right angles to each
other!
Write the Electron-Dot Formula for SeF2
Se
F
F
Because “F” is in
Group 17, they have
7 valence e-s, so they
must have 7 red dots
around them.