Section 12.1
Characteristics of Chemical Bonds
Objectives
1. To understand why atoms form bonds
2. To learn about ionic and covalent bonds and explain
how they are formed .
3. Define a polar covalent bond
Section 12.1
Characteristics of Chemical Bonds
Ch. 12 Chemical Bonding - Preview
1. When representing a water molecule as H--O--H, what
do the lines between the letters represent?
Bonds, attractive forces
2. Write the electron configurations for Fluorine, Neon, and
Sodium
F
1s22s22p5
Ne
1s22s22p6
Na
1s22s22p63s1
Section 12.1
Characteristics of Chemical Bonds
Why do atoms form bonds?
What happens when two
atoms get close together?
What is a chemical bond?
• An electrical attraction
between nuclei and valence
electrons of different atoms.
• A bond represents the
minimum potential energy for
two atoms.
Section 12.1
Characteristics of Chemical Bonds
A. Types of Chemical Bonds
• Bond – an attractive force (electrostatic) between atoms.
• Bond energy – energy stored in chemical bonds;
measured as the energy needed to break a bond;
describes the strength of a bond.
Section 12.1
Characteristics of Chemical Bonds
A. Types of Chemical Bonds
Ionic Bonding
(a)
(b)
• Ionic compound results when a metal reacts with a
nonmetal
• Transfer of electrons from one atom to another
• Force between oppositely charged ions
Section 12.1
Characteristics of Chemical Bonds
A. Types of Chemical Bonds
Covalent Bonding
• A covalent bond results when electrons are shared two
atoms
Section 12.1
Characteristics of Chemical Bonds
A. Types of Chemical Bonds
Covalent Bonding
• A polar covalent bond results when electrons are shared
unequally
– One atom attracts the electrons more than the other atom
Section 12.1
Characteristics of Chemical Bonds
B. Electronegativity
• Electronegativity – the relative ability of an atom in a
molecule to attract shared electrons to itself
– Increases from left to right across a period
– Decreases down a group of representative elements
Section 12.1
Characteristics of Chemical Bonds
B. Electronegativity
• The polarity of a bond depends on the difference
between the electronegativity values of the atoms
forming the bond
Section 12.1
Characteristics of Chemical Bonds
Electronegativity
Section 12.1
Characteristics of Chemical Bonds
Electronegativity
Electronegativity
Difference
< 0.4
0.4 < x < 1.9
> 1.9
Bond Type
Nonpolar covalent
Polar covalent
ionic
Section 12.1
Characteristics of Chemical Bonds
B. Electronegativity
Section 12.1
Characteristics of Chemical Bonds
C. Bond Polarity and Dipole Moments
• A dipole moment results when a polar molecule has a
center for positive charge separate from a center for
negative charge
Section 12.1
Characteristics of Chemical Bonds
C. Bond Polarity and Dipole Moments
• Water molecule dipole moment
Section 12.1
Characteristics of Chemical Bonds
C. Bond Polarity and Dipole Moments
• The polarity of water affects its properties
– Permits ionic compounds to dissolve in it
– Causes water to remain liquid at higher temperature