General Chemistry I

Chapter 8

Basic Concepts of Chemical Bonding

Chemical Bonds

n    Three general types

n    Ionic

n   Electrostatic attraction between ions

n   Strongest of the bond types

n    Covalent

n   Sharing of electrons between 2 atoms

n    Metallic

n   Electrons free to move among several neighboring atoms

n   Not discussed in detail here.

 

Lewis Symbols

n    Shows electrons in valence shell

n    Dots indicate valence electrons

n    Show on the 4 sides of the elements

Octet Rule

n    Noble gases

n    Filled s and p orbitals

n   He – only has s orbital!

n    2 electrons

n   All others 8 electrons in outer shell

n    Octet rule (Part 1)

n   Ions (except H and second period cations) will tend to have 8 electrons in the valence shell

n   ‘Noble Gas’ configuration

Ionic Bonding

n     NaCl

n    2 Na + Cl2 -> 2NaCl

Electronic Configuration

n    Representative elements

n    Valence shell electrons always lost first

n    Lose or gain electrons to form noble gas configuration

n   Heavier representatives may have more than one ionic charge, representing loss of np electrons, and loss of np and ns electrons.

n    ‘Pseudo’ noble gas configuration

n   ns2 np6 nd10 (n-1f14)

n   Ga – 3s2 3p6 3d10

n    Transition elements

n    First electrons lost are always from the valence shell

n    ns shell

n   All other electrons lost from the n – 1 d shell

n    Polyatomic ions

n    Anions – extra electrons for stability

n    Mix of ionic/covalent bonding

Problems:  1 – 9 odd

Sizes of Ions

n    Ionic size important for a number of reasons

n    Crystal formation

n    Biological activity

n    etc…

n    Depends on charge, # of electrons, and valence shell

Size Trends

n    Cations smaller than atoms

n    Anions larger than atoms

n    In a family, top to bottom gives larger ions

n    Isoelectronic species

n    Same electronic configuration

n    The more positive the ion, the smaller the ion for an isoelectronic series

Problems:  21 – 27 odd