Transcript The Quantum Mechanical Model of the Atom

Covalent
Bonding
Chapter 8
Introduction
• The bonds that hold atoms of molecules
together are fundamentally different from
those of ionic compounds.
• The types of atoms that comprise
molecules are more limited than ions.
• The properties of molecules are different
from ionic compounds.
• These properties are a result of the
interactions between molecules.
Molecular Compounds
Section 8.1
• Molecules
and
Molecular
Compounds
• Molecular
Formula
Different Compounds Have
Different Bonding Interactions
Noble gas:
No interactions
Ionic compound:
Ionic Bonds
Metal:
Metallic Bonds
How about the following compounds?
What type of
interactions hold
these compounds
together?
I.) Molecules and Molecular
Compounds
Molecules: A neutral group of atoms joined
together by covalent bonds.
Molecular Compound: A compound composed
of molecules.
Water is a
molecular
compound
Made up of
many molecules
of water.
Covalent Bonds
The _________ of electrons between
two atoms.
• No atoms give up their electrons
completely, nor does any atoms take
electrons.
• You can think of the bond as a “tug of war”
between the atoms.
The Covalent Bond
We can use Lewis dot structures
to show the sharing of electrons.
Molecules Are Created from
Covalently Bonded Atoms
Properties of Molecular
Compounds
• All the molecules of a given molecular
compound are the same.
• Low melting points and boiling points
• Gases or liquids at room temperature
• Composed of atoms of two or more nonmetals.
II.) Molecular Formula
The chemical formula of a
molecular compound.
• A molecular formula shows _______________of
each element a molecule contains.
• _____________ after each symbol indicates the
____________of the element are in the
molecule.
• The subscripts are not necessarily the lowest
_____________________.
• Does not give any information about the
molecular compounds structure.
Let’s look at some formulas for
molecular compounds.
1.
2.
3.
4.
5.
NO
NH3
CH4
H 20
N2H2
How many atoms of each element are
present in each molecular compound?
The Nature of Covalent Bonding
Section 8.2
• The Octet Rule in
Covalent Bonding
• Single Covalent
Bonds
• Double & Triple
Covalent Bonds
• Bond Dissociation
Energies
I.) The Octet Rule in Covalent
Bonding
•
•
•
Atoms will strive to obtain the electron
configuration of _____________, if they can.
ns2np6
In covalent bonding, ______________usually
occurs so that atoms attain the electron
configuration of noble gases. There are
exceptions, however.
____________of Group 4A, 5A, 6A, and 7A
will form covalent bonds to meet their octet.
Three Types of Covalent Bonds
• Single bonds, double bonds, and triple
bonds.
• These different types of bonds are based
on the ___________________________
between to atoms.
• Each type of bond has different
characteristics.
– Bond length, bond strength
II.) The Single Covalent Bond
A covalent bond formed when two
atoms share ________of electrons.
• A single bond can be represented as two
dots between two atoms or a single dashed
line between them.
• We can use a structural formula to
describe the bonding between atoms.
Let’s see how hydrogen forms it’s bond.
Let’s see how water forms its bonds.
Let’s see how methane forms its bonds.
What happened with the electrons
that did not participate in bonding?
• These unshared electrons are known as
lone pairs and are represented as two
dots around the molecular compounds.
Let’s examine this with water.
Write the structural formulas for the
following molecules.
1. F2
2. H2O2
3. Cl2
III.) Double Bond and Triple
Bonds
Double Bond: A covalent bond formed
when two atoms share __________of
electrons.
• Electrons are shared so that both atoms of
the double bond can obtain a noble gas
configuration.
Try drawing the structural formulas for
the following double bonded compounds.
1. Formaldehyde (CH2O)
2. Ethylene (C2H4)
Triple Bond: A covalent bond formed
when two atoms share __________ of
electrons.
• Again, the sharing occurs so that both
atoms can obtain an octet in their outermost (valence) energy level.
Try drawing the structural formulas for
the following triple bonded compounds.
1. Hydrogen cyanide (CHN)
2. Ethyne (C2H2)
Examining Differences in the
Bonds
IV.) Bond Dissociation Energy
The energy required to break the bond
between two covalently bonded atom.
Polar Bonds and Molecules
Section 8.3
• Bond Polarity
• Polar
Molecules
• Attractions
Between
Molecules
I.) Bond Polarity
• Covalent bonds differ in the way the
electrons are shared.
• The character of the bonds depends on
the kind and number of atoms joined
together.
• The type of covalent bonding helps to
determine the properties of a molecule.
• Covalent bonds can be polar or nonpolar.
Comparing
Bond Types
(Nonpolar)
Nonpolar Covalent
Bonds
• Atoms of equal
“strength” pull on
the electrons.
• ______________
share electrons
equally.
• H2, O2, N2 are
examples.
Polar Covalent
Bonds
• A covalent bond in
which the
electrons _______
shared equally.
• The _________
atom will pull more
of the electrons to
itself.
Atom’s Strength =
Electronegativity
The ability of an
atom of an element
to _______ electrons
when the atom is
in a compound.
(Chapter 6)
Periodic Trend in
Electronegativity
Electronegativity Differences
& Bond Type
Electronegativity Most Probable
Difference
Type of Bond
Range
0.0 – 0.3
Nonpolar
covalent
0.4 – 0.9
Moderately
Polar Covalent
1.0 – 1.9
Very Polar
Covalent
≥ 2.0
Ionic
Example
H-H (0.0)
H-Cl (0.9)
H-F (1.9)
Na+Cl- (2.1)
Use the table to determine the type of
bond each pair of atom will form.
1. H, N
2. K, Cl
3. C, Cl
4. Cl,Cl
II.) Polar Molecules
• One end is
slightly
________, the
other slightly
_________.
• _________: A
molecule that
has two poles.
III.) Attraction Between
Molecules
• These are the _________________ forces.
• Intermolecular forces are ________ than ionic or
covalent bonds.
• These interactions determines the ___________
of molecular compounds at room temperature.
• Three types:
– Dipole interactions
– Dispersion forces
– Hydrogen bonds
Comparing Intermolecular and
Intramolecular Forces
Dipole Interactions
• These forces occur
between ________
molecules.
• The negative ends
are attracted to the
positive ends.
• These forces are
similar to but much
weaker than ______
interactions
Dispersion Forces
• Weakest of all
interactions
• Occurs between
__________
molecules.
• Induced charges
hold these molecules
together.
• Strength of this
interaction increases
with increasing # of
electrons.
Hydrogen Bonds
These are interactions in which a
__________ covalently bonded to a
very electronegative atom is also
weakly bonded to an _______________
of another electronegative atom.
• H-bonds are
about 5% the
strength of a
covalent bond.
• These bonds are
extremely
important in
determining the
properties of
water and many
biological
molecules.
Covalent
Bonding
Chapter 8
The End