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Chapter 5Chemical Bonding
The Covalent Bond
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Covalent or Ionic ???
Electronegativity – the attraction that an atom has for the electrons that it is sharing w/ another atom
Scale devised by Nobel Prize winner Linus Pauling
Based on scale with fluorine assigned 4.0, the highest value
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Forming Chemical Bonds
• According to the Lewis model– an atom may lose or gain enough electrons to
acquire a filled valence shell and become an ion. An ionic bondionic bond is the result of the force of attraction between a cation and an anion.
– an atom may share electrons with one or more other atoms to acquire a filled valence shell. A covalentcovalent bondbond is the result of the force of attraction between two atoms that share one or more pairs of electrons.
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Covalent Bonds
A chemical bond in which 2 atoms share a single of electron to form one bond
Examples F and H
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Covalent Bonds
Two nonmetal atoms form a covalent bond because they have less energy
after they bonded
H + H H : H = HH = H2
hydrogen molecule
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Double Covalent Bond
2 pairs of electrons are shared between 2 atoms
Example O2
O + O O::O
double bond
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Triple Covalent Bond
3 pairs of electrons are shared between 2 atoms
Example N2
N + N N:::N
triple bond
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Diatomic Elements
Elements that are naturally in molecules with 2 atoms each.
HONClBrIF (pneumonic) Existing as diatomic molecule yields a stable octet Gases that exist as diatomic molecules are H2,
F2, N2, O2, Cl2, Br2, I2
Examples Fluorine & Bromine
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Learning Check
Use the name of the element to name
the following diatomic molecules.
H2 hydrogen
N2 nitrogen
Cl2 _______________
O2 _______________
I2 _______________
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Solution
Use the name of the element to
name the following diatomic
molecules.
H2 hydrogen
N2 nitrogen
Cl2 chlorine
O2 oxygen
I2 iodine
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Lewis Structures
Other molecules having single covalent bonds
H2O
The hydrogens share their electrons w/ oxygen so that O has 8 e- and each H has 2 e-
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Covalent Bonds in NH3
Bonding pairs
H
H : N : H
Lone pair of electrons
(unshared pair)
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Drawing Lewis Structures
1. Determine the number of valence electrons in the molecule
2. Decide on the arrangement of atoms in the molecule
3. Connect the atoms by single bonds
4. Show bonding electrons as a single line; show nonbonding electrons as a pair of Lewis dots
5. In a single bondsingle bond, atoms share one pair of electrons; in a double bonddouble bond, they share two pairs, and in a triple bondtriple bond they share three pairs.
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Coordinate Covalent Bond
Bond in which only one atom donates electrons to form the bond
Sometimes an arrow is used to designate the coordinate covalent bond
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Chemical Bonding: The Covalent Bond Model cont’d
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Chemical Bonding: The Covalent Bond Model cont’d
← Fig. 5.10
Linus Pauling received the Nobel Prize in chemistry in 1954 for his work on the nature of the chemical bond.
© Bettman/CORBIS
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Electronegativity
The attraction of an atom for electrons is called its electronegativity.
Fluorine has the greatest electronegativity.The metals have low electronegativities.
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Chemical Bonding: The Covalent Bond Model cont’d
→ Fig. 5.11
Abbreviated periodic table showing Pauling electronegativity values for selected representative elements.
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Electronegativity
• Electronegativity:Electronegativity: a measure an atom’s attraction for the electrons it shares in a chemical bond with another atom– on the Pauling scale, fluorine, the most
electronegative element is assigned a value of 4.0, and all other elements are assigned values relative to fluorine
- -
Electronegativity increases
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Bond Polarity: Nonpolar
Nonpolar covalent bond Electrons are shared between atoms with
the same electronegativity values. Difference = 0 Examples:
N2 Br2
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Bond Polarity: Polar
Polar covalent bond Electrons are shared between different
nonmetal atoms Examples:O-Cl O-S N-Cl
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Chemical Bonding: The Covalent Bond Model
← Fig. 5.12
(a) In the nonpolar covalent bond present, there is a symmetrical distribution of electron density. (b) In the polar covalent bond present, electron density is displaced because of its electronegativity.
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Chemical Bonding: The Covalent Bond Model
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Learning Check
Identify the type of bond between the following atoms A. K-N1) nonpolar 2) polar 3) ionicB. N-O1) nonpolar 2) polar 3) ionic
C. Cl-Cl
1) nonpolar 2) polar 3) ionic
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Solution
A. K-N 3) ionic
B. N-O 2) polar, covalent
C. Cl-Cl 1) nonpolar, covalent
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To decide whether a bond is covalent or ionic find the difference in electronegativities
< 2.0 covalent
> 2.0 ionic
Try KF, MgS, Cl2
Covalent or Ionic ???
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Character of Bonds
Chemist find it better to express chemical bonds as % ionic and % covalent
Relates electronegativity to ionic and covalent percentages
Table 7.2 (p 159) in text
Try KF, MgS, Cl2
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Molecular Polarity
Just like bonds molecules can have polarity Look at
Molecule geometry atoms (how atoms are arranged in space)
Bond polarity
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Chemical Bonding: The Covalent Bond Model
Fig. 5.13
(a) Methane is a nonpolar tetrahedral molecule. (b) Methyl chloride is a polar tetrahedral molecule.
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Electronegativity
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Writing Formulas
Nonmetal/Nonmetal In covalent bonds, the element with the
lowest electronegativity is written first
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Chemical Bonding: The Covalent Bond Model
→ Table 5.1
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Chemical Bonding: The Covalent Bond Model
→ Table 5.2
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Naming of 2 Nonmetals
1. Name each element2. End the last element in –ide3. Add prefixes to show more than 1 atomPrefixesmon 1 hexa 6di 2 hepta 7 tri 3 octa 8tetra 4 nona 9pent 5 deca 10
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Learning Check
Fill in the blanks to complete the following names of covalent compounds.
CO carbon ______oxide
CO2 carbon _______________
PCl3 phosphorus
_______chloride
CCl4 carbon ________chloride
N2O _____nitrogen
_____oxide© Karen Timberlake
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Solution
CO carbon monoxide
CO2 carbon dioxide
PCl3 phosphorus
trichloride
CCl4 carbon tetrachloride
N2O dinitrogen monoxide
© Karen Timberlake
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Learning Check
A. P2O5
B. Cl2O7
C. Cl2
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Solution
A. P2O5 diphosphorus pentoxide
B. Cl2O7 dichlorine heptoxide
C. Cl2 chlorine
© Karen Timberlake
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Learning Check
• Examples– draw a Lewis structure for hydrogen
peroxide, H2O2
– draw a Lewis structure for methanol, CH3OH
– draw a Lewis structure for acetic acid, CH3COOH
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Lewis Structures
Carbonic acidFormaldehydeAcetyleneEthylene
Hydrogen chlorideMethaneAmmoniaWater
H
H N H C H H ClH
HC C
HC C HH
HC
HHO
H
H2O (8) NH3 (8) CH4 (8) HCl (8)
C2H4 (12) C2H2 (10) CH2O (12) H2CO3 (24)
H
HHO
H
O OC HH
O
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3-D Characteristics of Molecules
Atoms and molecules have 3 dimensions Shapes of molecules lead to additional properties
of covalent compounds Polar covalent Bonding
When electrons are not shared equally between two atoms Bond that is certain % ionic
Nonpolar covalent Bonding Electrons are shared equally Diatomic atoms
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More Electron Pairs
Electron Angle Bonded Name of
Pairs Atoms Shape
4 109° 4 tetrahedral
4 109° 3 pyramidal
4 109° 2 bent, angular
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Shapes of Molecules
Number of electron pairs 2
(= negative charge clouds)
Number of bonded atoms 2
Angle 180°
Name of shape linear
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Electron Shape with 3 Pairs
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SO2
S has 2 bonded atoms , 1 lone pair (electron cloud)
120°, angular
.. .. .. :O:: S:O: S
.. O O