Covalent Bonding Chapter 9. What do the following have in common? Oil and Vinegar They are covalent...
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Transcript of Covalent Bonding Chapter 9. What do the following have in common? Oil and Vinegar They are covalent...
![Page 1: Covalent Bonding Chapter 9. What do the following have in common? Oil and Vinegar They are covalent compounds.](https://reader036.fdocuments.us/reader036/viewer/2022062516/56649e245503460f94b12962/html5/thumbnails/1.jpg)
Covalent Bonding
Chapter 9
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What do the following have in common?
Oil and Vinegar
They are covalent compounds.
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Review
Ionic bonds are formed by a transfer of e-
Metals + Nonmetals Ionic Compound
FU = Formula unit
smallest part of an ionic compound
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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
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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
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molecule
2 or more atoms combine covalently
Ex: carbohydrates, proteins, DNA, fibers
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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
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Double Bonds• Form because each element needs 2 e-
pairs
·:O:·+ ·:O:· ::O=O:: O2
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Triple Bonds• Formed because 3 e- pairs are shared
between two elements
:N:· + :N:· :N Ξ N: N2
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Diatomic molecule2 atoms that bond together
Featuring
“H and the Sensational 7”
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• 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
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Draw Lewis Structures
• PH3
• H2S
• CO2
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Draw Lewis Structures
• PH3 ¨H—P—H
I
H
• H2S
• CO2
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Draw Lewis Structures• PH3
•H2S ֵ
H—S—H
¨• CO2
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Draw Lewis Structures
• PH3
• H2S
• CO2
:O=C=O:
¨ ¨
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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
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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
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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
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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
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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-
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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”
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Examples• CCl4
Carbon tetrachloride
• As2S3
Diarsenic trisulfide
• CO
Carbon monoxide
• CO2
Carbon dioxide
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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
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Name acidic solutions
• Acid formulas begin with an H
• H becomes hydro-
• The acid name comes from the second element or polyatomic ion name
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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+
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Examples
H2O
CH3Cl
An atom may be + with respect to one bond and – with respect to another in the same molecule
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More info
Electronegativity Difference
Bond Type
0 Nonpolar Covalent
0.1 – 1.7 Polar Covalent
Above 1.7 Ionic Bond
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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
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• 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)
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• Polar molecules are bent or pyramidal (with opposite charges on sides)
• Polar molecules can be linear, tetrahedral, or planar (with opposite charges on sides)
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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
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Comparison
Ionic Molecular
State at room temp
Crystalline solid Gas, solid, liquid
Boiling Point High Low
Melting Point High Low