2 Midterm and other things
Average: 70% Highe 92% st: Lowe 41% st: 1st-tim rs e
Final e : 50% xam Midte s & quizze 30% rm s: Labs: 15% Assignm nts: 5% e
2nd-tim rs e
xam Final e : 60% rm s: Midte s & quizze 35% e Assignm nts: 5%
S tarting We sday, March 29 dne
hort nd ve cture(base on that le d cture m rial or onepre 's ate vious) S quiz at thee of e ry le
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1
Chemical Bonding I: The Covalent Bond
Chapter 9
Valence electrons are the outer shell electrons of an atom. The valence electrons are the electrons that participate in chemical bonding.
Group 1A 2A 3A 4A 5A 6A 7A
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e- configuration ns1 ns2 ns2np1 ns2np2 ns2np3 ns2np4 ns2np5
# of valence e1 2 3 4 5 6 7
3
9.1
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9.1
The Ionic Bond
Li + F 1s22s1 22s22p5 1s Li e + Li+ +
-
Li+ F [He]2Ne]2p6 1s2[ 2s2 1s Li+ + eF Li+ F -
F F -
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9.2
A covalent bond is a chemical bond in which two or more electrons are shared by two atoms. Why should two atoms share electrons? F
-
+
F
-
F F
-
7e Lewis7e 8e structure of F2 8e
single covalent bond lone pairs
F
F
lone pairs
lone pairs
F F
lone pairs
single covalent bond
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9.4
Only 2 valence electrons participate in the formation of F2. These are called bonding electrons. The other nonbonding electrons are called lone pairs. These are the electrons that are not involved in covalent bond formation.
single covalent bond
lone pairs
F
F
lone pairs
lone pairs
F F
lone pairs
single covalent bond
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9.4
Lewis structure of water H + O + H H O H
-
single covalent bonds
or
H
O
H
2e8e 2e Double bond two atoms share two pairs of electrons C O O
double bonds
-
or
O
C
O
double bonds
Triple bond 8etwo 8e 8e atoms share three pairs of electrons N N or N N
triple- bond
triple bond
8
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8e 8e
9.4
Octet rule
An atom other than hydrogen tends to form bonds until it is surrounded by 8 valence electrons.
O C O N N O N H O C N H O
H O H
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Lengths of Covalent Bonds
Bond Type Bond Length (pm)
C-C C= C C C C-N C= N C N
Bond Lengths Triple bond < Double Bond < Single Bond
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154 133 120 143 138 116
10
9.4
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9.4
Polar covalent bond or polar bond is a covalent bond with greater electron density around one of the two atoms
electron poor region electron rich region
H
F
e- poor
-
F H e rich +
Electrostatic potential map of the HF molecule.
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9.5
Electronegativity is the ability of an atom to attract electrons in a chemical bond. Electron Affinity - measurable, Cl is highest
X (g) + eX-(g)
Electronegativity - relative, F is highest
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9.5
< 0.5 nonpolar covalent 0.5-1.9 polar covalent >1.9 ionic
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9.5
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9.5
Classification of bonds by difference in electronegativity Difference 0 Bond Type Pure covalent
2 Ionic 0 < and <2 , Nonpolar or Polar covalent
Increasing difference in electronegativity Covalent share ePolar Covalent partial transfer of eIonic transfer e-
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9.5
Classify the following bonds as ionic, polar covalent, or covalent: The bond in CsCl; the bond in H2S; and the NN bond in H2NNH2. Cs 0.7 H 2.1 N 3.0 Cl 3.0 S 2.5 N 3.0 3.0 0.7 = 2.3 Ionic
2.5 2.1 = 0.4 Nonpolar covalent 3.0 3.0 = 0 Covalent
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9.5