Transcript Covalent Bonding - Anderson High School

Covalent Bonding
Sharing of Electron Pairs:
Non-metal with Non-metal Atoms
Covalent Bonding
• Compounds that are
NOT held together
by an electrical
attraction, but
instead by a
sharing of electrons.
• Occur between
nonmetal atoms
with
electronegativity
differences less than
1.67
Covalent Bonding
H•
•H
Covalent Bonding
Covalent Bonding
A neutral group of atoms joined together by
covalent bonds is called a molecule. A
compound composed of molecules is called a
molecular compound.
The chemical formula for a molecule is called the
molecular formula.
Molecule Name
Molecular Formula
L-tryptophan
C11H12N2 O2
Lewis Projection
Covalent Bonding
Properties of Molecular Compounds:
• Composed of two or more nonmetals.
• Usually gases or liquids at room
temperature. But can be found in any
physical state at STP.
• Molecular compounds tend to have
lower melting and boiling points than
do ionic compounds.
• Do not conduct electricity. They form
nonelectrolytes. in solution.
Covalent Bonding
Do not conduct Reason: Molecular
electricity. They form compounds do not
nonelectrolytes. break apart into ions
in solutions.
Covalent Bonding
Molecular compounds
tend to have lower
melting and boiling
points than do ionic
compounds.
Reason: There are
no (or few and
weak) bonds holding
the molecules
together in molecular
compounds.
Molecular
Compound
(H2O)
Ionic
Compound
(NaCl)
intermolecular bonds
Dispersion forces caused by motion of
electrons (weakest
intermolecular
force). More
electrons = stronger
dispersion forces.
Diatomic halide
molecules are held
together by
dispersion forces.
gas
gas
liquid
solid
intermolecular bonds
dipole
interactions
hydrogen bonds
Weak bonds
between bonded
hydrogen and
some electron
dense species.
(F,O,N)
polar covalent bonds
Polar bonds have more
electrons on one side of
the bond than the other.
Electrons concentrate
around electronegative
elements.
polar covalent molecules
Polar molecules
have polar
bonds. A
molecule with
two poles is
called a dipole.
non-polar covalent bonds
Covalent Bonding
Predicting Molecular Geometries & Polarity:
• Atoms attain an octet (also called noble gas
electron configurations) by sharing electrons.
• The bonds that form from this sharing can be
single, double or triple. Triple bonds are shorter
and stronger than double bonds, which are shorter
and stronger than single bonds.
Covalent Bonding
How Do We Proceed?
1. Determine total number of valence
electrons
2. Based on usual bond numbers, identify
reasonable layout for atoms <VSEPR>
3. Place bonding electrons between atoms
to make usual number of bonds
4. Place remaining electrons as lone pairs
around atoms still lacking an octet
hybrid orbital geometries
hybrid orbital geometries
Covalent Bonding
H + C
1e1H
6C
4e-
Equivalent to:
H·
Outer e- only shown
2e-
·
·C ·
·
Covalent Bonding
H + C
H·
H·
·
·C ·
·
H·
H·
Outer e- only shown
Covalent Bonding
H + C
Positive nuclei
: :
H
H: C :H
H
Negative
electrons
2 e- at each H
8 e- at carbon
all atoms closed shell
Outer e- only shown
Covalent Bonding
H + C
Final Structure:
Tetrahedral
Covalent Bonding
H·
:
H + N
·N·
·
H·
H·
Outer e- only shown
Covalent Bonding
: :
H + N
2 e- at each H
H: N :H
H
8 e- at nitrogen
all atoms closed shell
Outer e- only shown
Covalent Bonding
H + N
Final Structure:
Trigonal
Pyramidal
Covalent Bonding
H·
:
H + O
·O:
·
H·
Outer e- only shown
Covalent Bonding
: :
H + O
2 e- at each H
H: O :
H
8 e- at oxygen
all atoms closed shell
Outer e- only shown
Covalent Bonding
H + O
Final Structure:
Bent
Covalent Bonding
:
H + F
:F:
·
H·
Outer e- only shown
Covalent Bonding
: :
H + F
:F:
8 e- at fluorine
all atoms closed shell
H
2 e- at H
Outer e- only shown
Covalent Bonding
H + F
Final Structure:
Linear
Covalent Bonding
Patterns for Major Elements:
• CH4
• NH3
• H2O
• HF
C = 4 bonds; all electrons
shared
N = 3 bonds; one lone pair
O = 2 bonds; two lone pairs
F = 1 bond; three lone
pairs
Covalent Bonding
Patterns for Major Elements:
• Carbon, group IV
4 Bonds
All e- shared
• Nitrogen, Group V
3 Bonds
1 Lone Pair
• Oxygen, Group VI
2 Bonds
2 Lone Pairs
• Fluorine, Group VII
1 Bond
3 Lone pairs
Covalent Bonding
Other Compounds Have Same Pattern:
C = 4 bonds; Cl (like F) = 1 bond
P (like N = 3 bonds; Br (like F) = 1 bond
Covalent Bonding
Other Compounds Have Same Pattern:
S (like Oxygen) = 2 bonds, 2 lone pairs
C = 4 bonds; O = 2 bonds, 2 lone pairs
Covalent Bonding
Multiple Bonds
• Atoms may share more than one pair of
electrons
• a DOUBLE BOND forms when atoms
share two pairs of electrons (4 e-)
• a TRIPLE BOND forms when atoms
share three pairs of electrons (6 e-)
• Total number of bonds per atom
unchanged
Covalent Bonding
Multiple Bonds
•C2H4 Valence e- = 12
4 Bonds, each carbon
•H2CO Valence e- = 12
Two bonds at oxygen
Covalent Bonding
Multiple Bonds
Total valence e- = 16 (Oxygen = 6 e-, each;
Carbon = 4 e-. Four bonds/C; 2 bonds oxygen
Total valence e- = 10 (H = 1, C = 4, N = 5)
Bonds: C = 4, N = 3, H = 1
Total valence e- = 18 (O = 6, Cl = 7, P = 5)
Bonds: Cl = 1, P = 3, O = 2