Date

Bonding

Overview

✤ What are bonds?

✤ Types of Bonds

✤ Ionic or Covalent?

✤ Drawing Bonds

✤ Naming Compounds

Bonds

✤ An attachment between atoms.

✤ Bonds have to do with the electrons (particularly the outside ones) in atoms.

✤ The amount of attraction between the atoms is related to the strength of the bond.

✤ Generally, bonds form so that atoms can achieve eight valence electrons (octet rule).

Classification of Bonds

Chemical Bonds

Secondary (weak)

Primary (strong)

ionic

covalent

metallic hydrogen/dipole

Van der Waals

Classification of Bonds

✤ Bonds

✤ ionic

✤ covalent

✤ metallic

Ionic Bonds✤ When atoms combine, they do so by trying to achieve an inert (noble)

gas configuration. In an ionic bond, one gives up electron(s).

✤ In an ionic bond, a cation is attracted to an anion.

✤ Sodium Chloride is a classic example (NaCl). Notice the Lewis Diagram

Covalent Bonds

✤ Covalent bonding involves the sharing of one or more pairs of electrons so that each molecule achieves an inert gas configuration.

✤ Hydrogen is a classic example is H2

Metallic Bonds

✤ The valence electrons become detached from the nucleus of individual atoms and are shared (like covalent). The positive ions are closely packed within a sea of delocalized electrons.

✤ They form between metals.

✤ Metals are malleable because they can slide over each other without breaking more bonds than are made.

✤ Ionic compounds are formed between metals on the left of the periodic table and non-metals on the right side. Generally groups 1-3 and 5-7. What is the difference in their electronegativity? Examples:

✤ Al and F in AlF3

✤ Al and Cl in Al2Cl6

✤ Al and O in Al2O3

✤ Al and Br in Al2Br6

Ionic or Covalent?

✤ If the electronegativity difference is greater than 1.7 to 1.9, the bond will be more ionic than covalent.

✤ Al and F (2.6) --> ionic

✤ Al and Cl (1.4) --> covalent

✤ Al and O (2.0) --> ionic

✤ Al and Br (1.3) --> covalent

Ionic or Covalent?

Drawing Lewis Diagrams for the Formation of Compounds

✤ It’s different for ionic and covalent compounds.

✤ Shows the charges and orientation of atoms... very useful

✤ How do we do it?

Homework

✤ Read about ionic and covalent bonds and their relation to electronegativity (227-241).

✤ Do “Lewis Diagrams of Ionic and Covalent Compounds”