unit 11 covalent bonding
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Covalent Bonding
Unit 11
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Covalent Bonds• Involve sharing outer energy level
electrons.
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How Are They Different Than Ionic?
• Ionic bonds work by electromagnetic attraction. A positively charged ion is attracted to a negative ion.
• Covalent bonds work by sharing electrons. They do not have charges, but are hard to separate due to this sharing.
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ClClHow will two chlorine atoms react?
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ClClEach chlorine atom wants to gain one electron to achieve an octet
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Cl Cl
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Cl Cl
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Cl Cl
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Cl Cloctet
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Cl Cl
circle the electrons foreach atom that completestheir octets
octet
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Cl Cl
circle the electrons foreach atom that completestheir octets
The octet is achieved byeach atom sharing theelectron pair in the middle
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Cl Cl
circle the electrons foreach atom that completestheir octets
The octet is achieved byeach atom sharing theelectron pair in the middle
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Cl Cl
circle the electrons foreach atom that completestheir octets
This is the bonding pair
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Cl Cl
circle the electrons foreach atom that completestheir octets
Single bonds are abbreviatedwith a dash
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Cl Cl
circle the electrons foreach atom that completestheir octets
This is the chlorine molecule,
Cl2
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Covalent Bonds• Each oxygen has 6 valence
electrons and wants two more to have a full octet.
6 electrons6 electrons
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Covalent Bonds• If one oxygen shares two
electrons with the other, the other has a full octet.
8 electrons – happy!4 electrons left
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Covalent Bonds• But, then the other oxygen is
short, so it pulls them back.• Now the other oxygen shares 2
electrons4 electrons left8 electrons – happy!
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Covalent Bonds• Thus, by each of them sharing
two electrons back and forth, they both are at the full octet simultaneously.
8 electrons8 electrons
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OO
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OO
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OO
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OO
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OOBoth electron pairs are shared.
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OOBoth electron pairs are shared.
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So Who Covalently Bonds?
• Alkaline or Alkali Earth Metals do not form covalent bonds!
• Also Halogens are rarely covalently bonded.• Mostly it is non-metals in groups 3,4,5, and 6
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Electron Distribution
C.
...
Electrons occur in 4 fours separated as far
apart as possible
Valence Electrons: 4
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Electron Distribution
N ... C
...
.Electrons occur in 4
fours separated as far apart as possible
Valence Electrons: 4 5
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Electron Distribution
N ... C
...
. ..OElectrons occur in 4
fours separated as far apart as possible
Valence Electrons: 4 5 6
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Electron Distribution
N ... C
...
. ..OElectrons occur in 4
fours separated as far apart as possible
Secret Question: Why do electrons first fill orbitals one at a time before pairing up?
Valence Electrons: 4 5 6
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Electron Distribution
N ... C
...
. ..OElectrons occur in 4
fours separated as far apart as possible
Secret Question: Why do electrons first fill orbitals one at a time before pairing up?It is because electrons repel each other and want to be as far apart as possible.
Valence Electrons: 4 5 6
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Exception to Octet Rule
• Boron only has 3 valence electrons, so it is impossible to get to eight via covalent bonding
• Without 4 valence electrons, the shape of the molecule flattens out.
B..
. BH3
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Single Bond
• Ethane is C2H6
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Double Bond
• Ethene is C2H4
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Triple Bond
• Acetylene is C2H2
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Quadruple Bond???
• Can not occur, because the last bond can not bend all the way around.
Too far to bend
Too far to bend
Especially since triple bonds are so rigid
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Possible Covalent Bonds• Only where single electrons are located, can covalent
bonds be made.• Carbon has 4 single electrons, thus it can make 4 bonds.
• Nitrogen has 3 single electrons, thus it can make 3 bonds.
• Oxygen has 2 single electrons, thus it can make 2 bonds.
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Double Bonds Revisited
• Since Oxygen can make two bonds, and Carbon can make four, it makes for some interesting combinations.
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Why Carbon is the Key to Life• It is precisely because carbon can make 4 bonds, as
well as, double and triple bonds, that makes it so critical to life.
• Carbon chains can form virtually every formation possible.
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DNA and the building blocks for life
• Carbon, plus two other flexible elements, oxygen and nitrogen form the backbone of DNA
• DNA contains the genetic code for the building of life out of the largest of all molecules, proteins.
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Proteins are the largest molecules known