IIIIIIIV Chemical Bonding Chapter 6 Section 1 & 2 Pages 175-189.
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Transcript of IIIIIIIV Chemical Bonding Chapter 6 Section 1 & 2 Pages 175-189.
I II III IV
Chemical Bonding
Chapter 6
Section 1 & 2
Pages 175-189
Chemical Bond Attractive force between atoms or
ions that binds them together as a unit.(valence e- of one atom attracted to the nucleus of another atom).
Bonds tend to form to decrease potential energy or increase
stability. Types are ionic or covalent.
Ionic Bond
A cation is attracted to an anion• Cation = positively
charged ion• Anion = negatively
charged ion
Octet Rule is followed!
Ionic Compounds
Tend to form a crystal lattice.
Highly ordered
Repeating pattern
Ionic Compound metal-nonmetal
Two or more elements are combined in a chemical bond by gaining or losing electrons that achieves the octet rule.
Covalent Bonding nonmetal-nonmetal
A covalent bond is formed by a shared pair of electrons between two atoms.
ElectronegativityUsing Electronegativity values one can determine
the % ionic character.Nonpolar-covalent, equal sharing of electrons.
Bonds having 0% to 5% ionic character. Electronegativity differences of 0 to 0.3.
Polar-covalent, unequal sharing of electrons. Bonds having 5% to 50% ionic character. Electronegativity differences between 0.3 to 1.7.
Ionic bonding, is a complete transfer of electrons. >50% ionic character. Electronegativity differences of 1.7 to 3.3
Molecule; nonmetal-nonmetal
A group of atoms united by covalent bonds. ( polar or non-polar covalent).
Diatomic Molecule
Molecular Substances
Substance made of molecules
DNA
*The law of Octet
Octet Rule:
Atoms tend to gain, lose, or share electrons in order to get a full set of valence electrons.
(usually 8 electrons)
Bond Length
Increases as you go down a group, because the atomic radius increases.
Shorter for multiple bonds.
Multiple Bond LengthTriple bond is shorter than double bond, which is shorter than single bond.
Why? The more electrons in a bond, the stronger the attraction to the positively charged nuclei of the bonding atoms.
Bond Energies KJ/molBond Energies- The amount of energy
required to break a chemical bond and form neutral isolated atoms.
In general the higher the bond energy required the stronger the attraction, the shorter the chemical bond. (Data table on page 182)
Exceptions to the Octet Rule
Exceptions are those that form bonds that either have less than 8e- or more than 8e-
Less than eight:
Hydrogen can form one bond that has 2e-
Boron forms three bonds that contains 6e-
More than eight:
Sulfur can form 6 bonds containing 12e-
Phosphorus can form 5 bonds containing 10e-
Lewis Dot Diagrams
Lewis Structures
The use of dots or other symbols to represent bonded and unshared electrons.
2 shared electronsmake a bond.
Lines show the bond between atoms in a compound.
Structural (lines= 2e- )
How to Draw Lewis Structures:
Step 1 (N) determine the number of electrons Needed for each atom in the compound. Grp’s 14,15,16,17 all need 8. Hydrogen needs 2.
Step 2 (A)determine the number of electrons Available, which is determined by the grp # .
Step 3 N – A = e- Shared (S)
Step 4 A - S = Unshared (U)
Example: Methane CH4
4(2) + 1(8) = 16e-
Step 1 = Electrons Needed N
CCarbon goes in the middle because it is the singular atom.
Step 2 = Electrons Available A
1(4) + 4(1) = 8e-
HH
HH
C
Bonds go between atoms
Each bond uses up 2 electrons
Step 2 = N – A = S
16 – 8 = 8e- Shared
HH
HH
4 Bonds use up 8 electrons (4 x 2 = 8)Unshared ? 8 – 8 = 0
Step 1 determine NStep 2 determine AStep 3 N – A = SStep 4 A – S = U
Step 1: Ammonia NH3
NNitrogen goes in the middle because it is the singular atom.
Arrange Atoms
HH
H
N
Bonds go between atoms (6e-)
Each bond uses up 2 e-
Step 2:Form Bonds
HH
H
N
N = 14 A = 8 S = 6 A – S = 2 Used up 6e- with bonds
2 unshared to complete the
octet You’re done!
complete the octet
HH
H••
Step 1 NStep 2 AStep 3 N – A = SStep 4 A – S = U
Example Formaldehyde CH2O
CYou would have to guess whether C or O goes in the middle?It is Carbon, because it can form the most bonds, and least electronegative!
Arrange Atoms
HH
O
C
Bonds go between atoms
Each bond uses up 2 electrons
Form Bonds
HH
O
C
Had total of 20e- from step 1 Used up 6e- with bonds Need 2 more e- on C Need 6 more e- on O NOT ENOUGH TO GO AROUND
NEED DOUBLE BOND.
Step 3:Distribute remaining electrons
HH
O
Need 2 more e- on carbon to complete octet!
C
Remember the Octet
Rule ! Carbon & Oxygen both
need 8e-. They get 8 by sharing 4
e- between them.
Double Bonds
HH
O••
••••
C Represent double bond
with a double line. You are done!
Double Bonds
HH
O••
••
Double bonds occur in these
molecular compounds;
Oxygen, Carbon Dioxide
Triple Bonds: Nitrogen
Multiple Bonds
Resonance StructuresMolecules that can’t be correctly
represented by a single Lewis diagram.Actual structure is an average of all the
possibilities.Show possible structures separated by a
double-headed arrow.
Example: SO3
OO S O
OO S O
OO S O