Transcript In covalent bonds

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 energy. Nature
favors a reduction in
this energy-by bonding,
they reduce their
potential energy.
Remember….for atoms
to be most stable 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.
**Review valence
electrons!!!!!
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
Example Problems
1. Ca
5. Br
2. K
6. C
3. Ar
7. He
4. Al
8. O
Types of Bonds
• Ionic
• Covalent
• 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
Covalent bonding
• Results from the
sharing of electron
pairs between two
atoms.
• Groups of atoms
held together by
covalent bonds are
called molecules.
Properties of Covalent Bonds
•
•
•
•
•
Low melting and boiling points
Form between two nonmetals
Form by the sharing of electrons
Often liquids or gases at room temp.
Will either be nonconductors or poor
conductors of electricity
Lewis Structures
Shows electrons being shared in covalent
bonds as well as any unshared electrons
(also called a lone pair) that are not
involved in bonding.
Examples:
1). H and H
2). F and F
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)
Remember…..
• Ionic are generally stronger bonds than
covalent.
• In covalent bonds:
Polar bonds are stronger than nonpolar
• In intermolecular forces:
H-bonding is strongest, then dipoledipole,then dispersion forces