Chemical Bonding
How compounds are held together
Review Questions
When representing a water molecule as H-O-H, what do the
lines represent?
Write e- configs for argon, chlorine, neon, and sodium
Ar = 1s2 2s2 2p6 3s2 3p6
Cl = 1s2 2s2 2p6 3s2 3p5
Ne = 1s2 2s2 2p6
Na = 1s2 2s2 2p6 3s1
Why is the phrase “sodium chloride molecule” incorrect?
Objectives
Learn about ionic and covalent bonds and explain how they
are formed
Learn about polar covalent bonds
Understand nature of bonds and their relationships to
electronegativity
Understand bond polarity and how it is related to molecular
polarity
What is a BOND???
Force holding two or more
atoms together
Makes atoms function as a
unit
Strength of the force =
energy required to break
bond = bond energy
Types of bonding
Focus on two types of
chemical bonds:
IONIC BONDING
COVALENT BONDING
Ionic Bonding
Oppositely charged ions - strong
bonding force
Electron is transferred to another
atom
Metal + NonMetal
e- from Na transferred to Cl.
Na atom stable (“looks” like Ne)
Cl is stable (“looks” like Ar)
QuickTime™ and a
GIF decompressor
are needed to see this picture.
Covalent Bonds
Atoms share e2 Cl atoms share eBoth Cl stable (both “look”
like Ar)
Occurs between nonmetallic atoms
QuickTime™ and a
GIF decompressor
are needed to see this picture.
Polar Covalent Bond
• Sometimes, there is an
unequal sharing of the
electrons
• Known as Polar Covalent
bond.
• Partial charge on atoms
shown using lower case
greek letter delta ∂
Questions
What is meant by the term chemical bond? What subatomic
particles are most important in bonds?
How are ionic bonds and covalent bonds different?
How is a polar covalent bond different from a covalent bond?
Objectives
Learn about ionic and covalent bonds and explain how they are
formed
Learn about polar covalent bonds
Understand nature of bonds and their relationships to
electronegativity
Understand bond polarity and how it is related to molecular
polarity
Nature of bonds
Type of Bond
What happens to
Element Types
e-
Transferred to
other atom
Na + Cl
NonMetal +
Pure Covalent
NonMetal
Equally Shared
Bond
(Same Element)
Cl + Cl
NonMetal +
Polar Covalent
NonMetal
Bond
(Diff. Elements)
H + Cl
Ionic Bond
Metal +
NonMetal
Example
Unequally
Shared
Electronegativity
Ability of atom in
molecule to attract shared
e- to itself
Increases going left to right
across periodic table
Decreases going down a
group
Electronegativity
Range: Fluorine 4.0...Francium & Cesium 0.7
Effect: Higher electronegativity of an atom, the closer shared
e- will be to that atom when it forms a bond
Electronegativity
Bond Polarity
Bond Polarity depends on difference in electronegativity
values of atoms forming bond
Atoms with very different electronegativities form very
polar bonds
Ionic bonds are extreme case of bond polarity
Electronegativity difference greater than 2.0 considered ionic
bond
Bond Polarity Continuum
Thinking question...
How do electronegativity
trends compare to trends of
atomic size?
Problem
Arrange the following bonds
in order of increasing
polarity: H-H, O-H, Cl-H, SH, F-H
Selected Electronegativity
Values
Silicon
1.8
Hydrogen
2.1
Phosphorous
2.1
1. H-H (2.1 - 2.1 = 0.0)
Sulfur
2.5
2. S-H (2.5 - 2.1 = 0.4)
Carbon
2.5
3. Cl-H (3.0 - 2.1 = 0.9)
Nitrogen
3.0
Chlorine
3.0
Oxygen
3.5
Fluorine
4.0
4. O-H (3.5 - 2.1 = 1.4)
5. F-H (4.0 - 2.1 = 1.9)
Problems
For each of the following
bond pairs, choose the one
that is most polar
H-P & H-C
(2.1 - 2.1) < (2.5 - 2.1)
H-C
O-F & O-Cl
(4.0 - 3.5) = (3.5 - 3.0)
same
N-O & S-O
(3.5 - 3.0) < (3.5 - 2.5)
S-O
N-H & Si-H
(3.0 - 2.1) > (2.1 - 1.8)
N-H
Selected Electronegativity
Values
Silicon
1.8
Hydrogen
2.1
Phosphorous
2.1
Sulfur
2.5
Carbon
2.5
Nitrogen
3.0
Chlorine
3.0
Oxygen
3.5
Fluorine
4.0
Match the compounds HF, NaCl, and O2 with the figures
above
How do electronegativity values help in determining the
polarity of a bond?
Objectives
Learn about ionic and covalent bonds and explain how they are
formed
Learn about polar covalent bonds
Understand nature of bonds and their relationships to
electronegativity
Understand bond polarity and how it is related to
molecular polarity
Bond Polarity & Molecular Polarity
Molecule such as H-F that has
a center of positive charge
(∂+) and a center of negative
charge (∂-) is said to have a
dipole moment
Dipole moment represents
molecular polarity
Any diatomic molecule with a
polar bond has a dipole
moment
Some Polyatomic Molecules have
dipole moments
Water is a polar molecule
(it has a dipole moment)
Properties of H2O
surrounds and attracts both + and
- ions
dissolves ionic substances
attract one another strongly (hbonds)
high boiling temperature
Questions
For each binary molecule
given, indicate direction of its
dipole moment. Some may
have no dipole moment.
H-Cl
H-H
H-I
Br-Br
C-O
Summary
Chemical bond = force holding 2 or more atoms together
Types of Bonds = Ionic and Covalent
Ionic = transfer of eCovalent = sharing of ePolar Covalent = unequal sharing of eElectronegativity = how much an atom “pulls” on ePolar bonds -> polar molecules