Covalent Bonds
http://www.ptable.com
• Octet Rule must be satisfied-reach noble gas
state
• What of elements that meet and cannot
completely transfer e- and satisfy octet rule
for each?
• H and H atom story…one happy if e- tranfer
other sad
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Both atoms get one eBoth satisfy octet rule by SHARING
Each atom must have both eDIRECTIONAL bond- product of shared eEach H atom will have full outer energy level
Hydrogen gas H2
• Two H atoms sharing each other’s e-
• Oxygen gas shares 4 valence e- or
2 pairs valence e• Results in a double bond
• Nitrogen gas shares 3 pairs of valence e• Results in triple bond
• Hydrogen, fluorine, nitrogen, chlorine…
• BrINClOF (Chlorine is capital C lower case l)
Remember how to do this?
1s2…
• Each bond represents 2 shared e-
Nature of Covalent Bonds
• Strong electrostatic attraction between shared
valence e- and + nucleus
• One end of molecule has more + than
– charge
Draw Lewis dots and show how water
molecule shares e• Covalent bond VERY STRONG
• Shared e- confined so bond is
DIRECTIONAL
Covalent vs. Ionic Bonds
• http://www.mhhe.com/physsci/chemistry/ani
mations/chang_7e_esp/bom1s2_11.swf
http://www.bing.com/videos/search?
q=ionic+vs+covalent+bonding&FORM
=VIRE3&adlt=strict#view=detail&mid=
• video
D0981F9E5
H tends to share only e- Octet rule
not satisfied by giving up e•
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ᵟ
H and Cl… HCl
Chlorine tends to grab at eDoesn’t want to give it up…
Uneven distribution of e- density
ELECTRONEGATIVITY becomes important
small delta indicates charge – or +
ᵟ+
H Cl
ᵟ-
Result is…
• POLARITY
• A partial charge separation
• Electronegativity increases e- moves towards
the area
• In covalent bonds, neither atom has energy to
remove e- from other atom
Example of a polar covalent molecule
• H-O-H Water H2O
• Stable octet for oxygen.. Completed with
other H atom
Notice how directional the bonds are
for water- a covalent molecule
• Polarity of water makes it the universal
solvent.. Able to dissolve many substances..
• Not all!!
Non Polar Molecules
• Even distribution of charge
• Examples: oxygen gas O2
Cov vs. Ionic Bonds
Electronegativity counts
• Hydrogen Gas molecule: H2
No difference of attraction of electrons
between 2 atoms so ΔEN=O
(Capital Delta Δ means change)
Hydrogen gas is a non polar covalent molecule
Water is polar covalent
EN and bond types
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0 = non polar cov
< 0.3 no polar cov
0.3- 0.4 slightly polar cov
1.0-1.7 polar cov
More and more separation of charges
If difference > 1.7 then generally ionic!
Go to ptable.com
• http://www.ptable.com
Your Turn
• Use EN # on PT to determine difference in EN
between elements of a compound and type of
bond formed between them.
NaBr
Water
CS2
Inter and Intra prefixes
• Forces may be intra or intermolecular in nature.
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H:H molecule of hydrogen gas
Can 3rd H come into the molecule?
No Pauli Exclusion Principle
Molecules formed with hydrogen gas.
Bond very strong .. What’s in between
molecules?
BLACK Intra Forces-within moleculeRED Inter Forces- between or among
molecules as they exist in natural state
Intermolecular forces weaker than intramolecular forces
The unit formed is called a molecule
Properties of Covalent (diatomic)
Elements and Compounds
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Dull no free eSoft, brittle- weak intermolecular forces
Low mp and bp- weak intermolecular forces
NO conductivity as solid or molten (no
charges)
• Some soluble in water Aqueous solutions DO
NOT conduct electricity at all- no free moving
charged particles
• Diamond and graphite examples of Carbon in
covalent bonding
• Microstructures in diamond very different from
graphite
• Both covalent, both made of carbon only
• Diamond- strong interactions of directionality of
carbon atoms- lattice like STRONG BONDS
• Graphite- weaker bonds due to direction and
spaces between atoms allows for breakageleaving of powder from pencil
diamond
graphite
Molecular Compounds Nomenclature
• State how many of each element in compound
• Water H-O-H
• FIRST: must know prefixes:
1. 1. Mono
2. Di
3. Tri
4. Tetra
5. Penta
6. Hexa
7. Hepta
8. Octa
9. Nona
10. Deca
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Communicate first element
Assume same name as element’s name
2nd element “ide” notation
ONE exception: if 1 is coefficient for 1st
element then it is dropped
• WATER? Dihydrogen monoxide
Your Turn
• N2O5
• Carbon dioxide.. To write this
formula properly, what is
dropped?
• Sulfur trioxide
• SF6