covalent bonding chapter 9. what do the following have in common? oil and vinegar they are covalent...
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Covalent Bonding
Chapter 9
What do the following have in common?
Oil and Vinegar
They are covalent compounds.
Review
Ionic bonds are formed by a transfer of e-
Metals + Nonmetals Ionic Compound
FU = Formula unit
smallest part of an ionic compound
Apply the octet rule to atoms that bond covalently
Octet Rule:Atoms will gain e-, lose e- or share e- in order to
get 8 valence e- to be stable
Covalent Bond
Sharing of e- to be stable
Usually occurs when elements are close on periodic table
NM + NM covalent compound
aka: molecular compoundhttp://school.discovery.com/clipart/category/anmt.html
molecule
2 or more atoms combine covalently
Ex: carbohydrates, proteins, DNA, fibers
Describe the formation of single, double and triple covalent bonds
• Single bond – formed because only 1 e- pair is shared
between 2 elements
• These elements need only one additional e- to be stable– Ex: hydrogen and the halogens (Group 7A)
H·+·H H– H H2
Double Bonds• Form because each element needs 2 e-
pairs
·:O:·+ ·:O:· ::O=O:: O2
Triple Bonds• Formed because 3 e- pairs are shared
between two elements
:N:· + :N:· :N Ξ N: N2
Diatomic molecule2 atoms that bond together
Featuring
“H and the Sensational 7”
• Covalent bonds are formed by diatomic molecules
• Different nonmetals can share e- to be stable and form covalent bonds
• By drawing e- dot structures of each atom, you can put them together so each has 8 valence e- making a
LEWIS STRUCTURE
Draw Lewis Structures
• PH3
• H2S
• CO2
Draw Lewis Structures
• PH3 ¨H—P—H
I
H
• H2S
• CO2
Draw Lewis Structures• PH3
•H2S ֵ
H—S—H
¨• CO2
Draw Lewis Structures
• PH3
• H2S
• CO2
:O=C=O:
¨ ¨
Relate the strength of covalent bonds to bond length
• The more bonds located between 2 atoms, the shorter the bonds are
• The shorter a bond is, the stronger it is
H – H single bond, not too strong
O=O double bonds, stronger
NΞN triple bonds, strongest
Review 9.1
• When 2 Nonmetals form a compound, they SHARE e-
• This is a covalent bond
• The compound formed is a molecular compound
• The smallest part of a molecular compound is a molecule
Bond Type Ionic Bond Covalent Bond
Elements M + NM
Polyatomic Ion
NM + NM
Atoms become stable by
Gain/Lose e- SHARE e-
Name of Compound
Ionic compound Molecular Compound
Smallest Particle
Formula Unit (FU)
Molecule
9.2 Naming molecules
Identify the names of binary molecular compounds from their formulas
Molecules are formed when nonmetallic atoms share e-
They can combine in different ratios, such as CO and CO2; therefore, PREFIXES are used in the name
PREFIXES
• KNOW the prefixes on table 9-1 (p. 248)
1 mono- 6 hexa-
2 di- 7 hepta-
3 tri- 8 octa-
4 tetra- 9 nona-
5 penta- 10 deca-
Using prefixes
• The prefix “mono” is NEVER used for the first element, but all prefixes are
• When the element begins with a vowel (O, I), you drop the a or o from the prefix
• The second element always has a prefix and ends in “-ide”
Examples• CCl4
Carbon tetrachloride
• As2S3
Diarsenic trisulfide
• CO
Carbon monoxide
• CO2
Carbon dioxide
Writing Formulas
• When writing formulas for molecular compounds, use prefixes to tell how many atoms are in the molecule
• Sulfur dioxide
SO2
• Diphosphorous pentoxide
P2O5
Name acidic solutions
• Acid formulas begin with an H
• H becomes hydro-
• The acid name comes from the second element or polyatomic ion name
Naming acid
2nd name ends in • -ide
HCl (chloride)
HF (fluoride)
• -ate
• -ite
Acid name• Hydro ____ic acid
Hydrochloric acid
Hydrofluoric acid
• ___ic acid
• ___ous acid
Naming acid
2nd name ends in • -ide
• -ate
H2SO4 (sulfate)
HNO3 (nitrate)
• -ite
Acid name• Hydro ____ic acid
• ___ic acid
sulfuric acid
nitric acid• ___ous acid
Naming acid
2nd name ends in • -ide
• -ate
• -ite
HClO3 (chlorite)
H3PO3 (phosphite)
Acid name• Hydro ____ic acid
• ___ic acid
• ___ous acid
Chlorous acid
Phosphorous acid
Naming acid
2nd name ends in • -ide
HCl (chloride)
HF (fluoride)
• -ate
H2SO4 (sulfate)
HNO3 (nitrate)
• -ite
HClO2 (chlorite)
H3PO3 (phosphite)
Acid name• Hydro ____ic acid
Hydrochloric acid
Hydrofluoric acid
• ___ic acid• sulfuric acid
nitric acid• ___ous acid
Chlorous acid
Phosphorous acid
Writing Acid Formulas• The first element in an acid is ALWAYS H+
• To find the second, use the same chart, work backwards:
-ide hydro__ic acid
-ate ___ic acid
-ite ____ous acid
Example: Phosphoric acid
___ ic acid means the second name ends in –ate
Phosphate is the second name
Hydrogen phosphate (now use charges and criss cross)
H+ PO4 3-
H3PO4
9.3 Molecular Structure
• Structural formulas = uses letter symbols and bonds to show relative position of atoms (same as Lewis Structure)
• Chem I:– Don’t need definition of resonance or
coordinate covalent bond– Only need step 1 of drawing Lewis structures– Don’t need obj. 2, 3, of 9.3
Rules
*1. Predict location of certain atoms
a) Hydrogen is always terminal (end) atom
b) Atom with least e- affinity (furthest to left on periodic table) is central atom
9.4 Molecular Shape
VSEPRValence Shell Electron Pair Repulsion Theory
States:
Repulsion of shared and unshared pairs (lone pairs) of e- around the central atom shapes the molecule
Table 9-3• Look at a correctly drawn structural
formula
• Count the number of shared pairs and lone pairs on the CENTRAL ATOM
• Compare to the table
• Examine table 9-3 examples on p. 260
Atoms in Molecule
Lone pairs on central atom
Molecule Shape
2 Linear
3 None Linear
3 Lone pair Bent
4 None Trigonal planar
4 Lone pair Trigonal pyramidal
5 tetrahedral
9.5 Electronegativity & Polarity
Electron Affinity
is the ability of an atom to accept an e-
• Excluding noble gases, e- affinity increases to the right of the periodic table
• Electron affinity increases going up in a group
Electronegativity
• Assigned values for elements that compare the ability of an atom to attract shared e- to itself to the ability of Fl to do the same
• Has the same trend as e- affinity
Bond Polarity
To determine if a bond is polar or not: (polar means having a negative and positive side)
– Compare the electronegativity of each atom connected by the bond
– The atom that is further to the right (or in the same group: further up) will hold the e- closer and be σ-
– The other atom will be σ+
Examples
H2O
CH3Cl
An atom may be + with respect to one bond and – with respect to another in the same molecule
More info
Electronegativity Difference
Bond Type
0 Nonpolar Covalent
0.1 – 1.7 Polar Covalent
Above 1.7 Ionic Bond
Molecule Polarity
To determine if the entire molecule is polar (has a negative and positive side) or not, you must look at 2 things
1. molecule shape
2. bond polarity
If the molecule contains only nonpolar bonds, then the molecule is also NONPOLAR
• If the molecule has polar bonds, it may be a NONPOLAR or a POLAR molecule, depending on the shape
• Nonpolar molecules are usually linear (with same charge on all sides); tetrahedral (with same charges on all sides); planar (with same charge on all sides)
• Polar molecules are bent or pyramidal (with opposite charges on sides)
• Polar molecules can be linear, tetrahedral, or planar (with opposite charges on sides)
Properties of Molecular Compounds
• REVIEW: Ionic compounds were crystalline solids at room temp with high melting points and high boiling points
• Molecular compounds may be gases, liquids or solids at room temp
• Molecular compounds have LOW melting points and LOW boiling points
Comparison
Ionic Molecular
State at room temp
Crystalline solid Gas, solid, liquid
Boiling Point High Low
Melting Point High Low
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