Transcript Ionic vs Covalent Bonding

Covalent Bonding Notes
Ionic vs Covalent Bonding
• Ionic: electron(s) leave one atom & gained by
another atom to satisfy both atoms’ octets,
this results in the formation of ions. The
resulting opposite charges attract each other.
• Covalent: electrons are shared by two or more
atoms to satisfy their octets.
How can you tell if a bond is IONIC or
COVALENT?
• Subtract the two electronegativity values
>1.7 to 4.0: Ionic
>0.4 to 1.7: Polar Covalent
0.0 to 0.4: Non-Polar Covalent
• Electronegativity: atom’s ability to attract electrons
in a chemical bond. (higher electronegativity means
the atom wants electrons more)
How can you tell if a bond is IONIC or
COVALENT?
• Easy way:
All metals = metallic bond
Nonmetals and Metals = ionic bond
All nonmetals = covalent bond
Yes, there are 2 kinds of covalent
bonds!
• Polar covalent: the electrons are shared, but
one atom is pulling on the electrons a lot
more. The electrons spend more time around
that atom.
• Nonpolar covalent: the electrons are evenly
shared between the two atoms.
O(3.5) – H (2.1) = 1.4
Polar covalent bond
Properties of Covalent
Compounds
1) Have much lower melting and boiling points
than ionic compounds.
2) Covalent compounds are soft and squishy
(compared to ionic compounds, anyway).
Properties, Cont’d
• 3) Covalent compounds tend to be more
flammable than ionic compounds.
– There are exceptions to this rule!
• 4) Do not conduct electricity in water.
• 5) Gases, liquids, or solids
The Convalent Bond
• The neutral particle is formed when atoms
share electrons is called a molecule
Bond Dissociation Energy
• Bond dissociation energy = energy required to
break a covalent bond.
Highest bond energy
Hardest to break
Triple
Bond
Shortest bond length
Strongest
Lowest bond energy
Easiest to break
Double
Bond
Single
Bond
Longest bond length
Weakest
Chemical Bonds
Bond Type
Single
Double
Triple
# of e’s
2
4
6
Notation
—
=

Bond order
1
2
3
Bond
strength
Bond length
Increases from Single to Triple
Decreases from Single to Triple
How to Draw Covalent Molecules
• EXAMPLE : CF4
• 1) Find the total number of electrons
• 2) Write the symbol for the single atom
surrounded by all the other atoms
– If there is not a single atom
• Use the first atom
• Use the most electronegative atom
• 3) Connect all the molecules by drawing a
single bond (a line)
• 4) Subtract the number of electrons that are
used from the total number of electrons
• 5) Distribute the remaining electrons so that
all atoms satisfy the octet rule
– *Remember when there is a line connecting
elements it represents 2 electrons*
• Place Double and Triple bonds when
necessary
Another Example
• Water
Another Example
• N2
Exceptions and special situations
– Hydrogen will only ever form a single bond and will never
have lone pairs around it.
– Boron can also have less than an octet because of the 3
valence electrons.
– Only atoms in the 3rd row and beyond can break the octet.
How to Name Covalent Compounds
• 1. Name the first element
(normal name)
• 2. Name the second element and change the
ending to –ide
• 3. Add prefixes to indicate how many atoms of
each element are in the molecule (Subscripts)
• Exception: no need to use “mono” for first
element. Example: CO2 = carbon dioxide
Prefixes
Subscript
prefix
1
2
3
4
Mono
DiTriTetra-
5
6
7
PentaHexaHepta-
8
9
OctaNona-
10
Deca-
Examples
• PH3
• CO
• N2O3
Examples
• Dinitrogen Hexafluoride
• chlorine dioxide
• iodine pentafluoride
Diatomics
• Diatomic elements are elements that do not
exist singularly in nature because they are
highly reactive.
“Which elements are the diatomics?”
“HON, it’s the halogens!”
• H2, O2, N2, F2, Cl2, Br2, I2