Section 12.1

Characteristics of Chemical Bonds

1. To understand the nature of bonds and their relationship to electronegativity

2. To understand bond polarity and how it is related to molecular polarity

Objectives

Section 12.1

Characteristics of Chemical Bonds

A. Types of Chemical Bonds

• Bond – force that holds groups of atoms together and makes them function as a unit

• Bond energy – energy required to break a chemical bond

Section 12.1

Characteristics of Chemical Bonds

A. Types of Chemical Bonds: Non-metals + Non-metals

A covalent bond results when electrons are shared by nuclei

Covalent Bonding: Sharing Electrons

Section 12.1

Characteristics of Chemical Bonds

A. Types of Chemical Bonds

• A polar covalent bond results when electrons are shared unequally by nuclei

Covalent Bonding

– 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 – Quantitative scale– Follows the same trends as ionization energy

– The higher an atom’s electronegativity value, the closer the shared electrons tend to be to that atom when it forms a bond.

Section 12.1

Characteristics of Chemical Bonds

Electronegativity Property

Section 12.1

Characteristics of Chemical Bonds

B. Electronegativity

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

As a general rule, if the difference in EN values is > 2.0, then the bond is considered to be ionic.

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

– Causes water to remain liquid at higher temperature

– Permits ionic compounds to dissolve in it