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A chemical bond is a mutual attraction
between nuclei and valence electrons of
different atoms that binds atoms together.
• Why do atoms form
bonds?
• As single particles,
atoms have a high
potential NRG.
Nature favors a
reduction in this
energy-by bonding,
they reduce their
potential NRG.
Remember….for atoms
to be most stable (i.e.
have the lowest
possible potential
NRG-they must have
their outermost shell
full of electrons.
• The Octet Rule
states:
Atoms require 8 valence
electrons to be stable
An exception is H and
He which only require
2.
Electron-Dot Notation
• Used to show
the number of
valence
electrons an
atom has-also
called Lewis Dot
Structures
Periodic Table w/ Electron Dot
Notations
Types of Bonds
• Ionic
• Covalent
• Metallic
• Results from the
electrical attraction
between a cation and
an anion
• Bonds are formed
when electrons are
transferred.
• By transferring
electrons-their
outermost shells
become filled.
Oxidation Numbers
• As electrons
are gained or
lost, the atom
takes on
either a
negative or
positive
charge which
is called an
oxidation
number.
• Oxidation Numbers Groups
1-18
Group
Oxidation #
1
+1
2
+2
13
+3
14
+4 or -4
15
-3
16
-2
17
-1
18
0
Two Types of Ions
• Monatomic
-ions that form from one
atom
Ex. Na+1
Cl-1
Mg+2
S-2
• Polyatomic
- Ions that form from
more than one atom
Ex. SO4-2 (sulfate)
NH4+1
(ammonium)
Characteristics of Ionic Bonds
•
•
•
•
High melting pts.
High boiling pts.
Hard and brittle
can conduct electricity
in solution
• Form between a
metal and a nonmetal
Electron Dot for Ionic Bonds
• Results from the
sharing of electron
pairs between two
atoms.
• Groups of atoms held
together by covalent
bonds are called
molecules.
Characteristics of Covalent Bonds
•
•
•
•
Form between two nonmetals
Have low melting and boiling pts.
Are generally weaker bonds
Results from the sharing of electrons
Covalent Bonds can be either:
• Polar
• Results from unequal
sharing of electrons
• Nonpolar
• Results from equal
sharing of electrons
Differences in electronegativity determine if a covalent
bond will be polar or nonpolar-the bigger the difference-the
more likely it will be polar
Intermolecular Forces
• These are forces that
occur between
COVALENTY
BONDED
ELEMENTS
•
Three types of
intermolecular
forces:
1. Dipole-Dipole (only
present in polar
molecules)
2. Hydrogen bonding
(only present in
polar molecules)
3. London dispersion
forces (present in
both polar and
nonpolar)
Dipole-Dipole
• The strongest
intermolecular forces
occur between polar
molecules because
they act as tiny
dipoles (created by
equal but opposite
charges separated by
a short distance)
• These oppositely
charged areas are
attracted to one
another.
Hydrogen Bonding
• Intermolecular force
in which a H atom is
bonded to a highly
electronegative atom
• This is a particularly
strong type of dipoledipole force
London Dispersion Forces
• Any atom or molecule
will experience weak
intermolecular forces
due to the continuous
motion of electrons.
• This movement
creates uneven
electron distribution
which creates a
temporary dipole.
• London dispersion
force- an attraction
resulting from uneven
electron distribution
and the creation of
temporary dipoles
• These are very weak
forces.
Remember…..
• Ionic are generally stronger bonds than
covalent.
• In covalent bonds:
H-bonding is strongest, then dipole-dipole,
then dispersion forces
• Chemical bond that
results from attraction
between metal atoms
and the surronding
“sea” of electrons
created by the
overlapping of orbitals
where electrons can
move freely
• Characteristics:
1. Good conductors of
heat and electricity
2. Absorb a wide range
of light frequencies
3. Malleable
4. Ductile
5. Form between two
metals