Chemical Bonding: Ionic

Lecture 1

Many, many, many properties, both chemical and physical,are determined by the type of bonding

within the substance.

Why do atoms bond at all?

Because bonding lowers the potential energy between positive and negative

particles.

The three types of chemical bonding:

Ionic based on electron transfer: metals with nonmetals;

Covalent based on electron sharing: nonmetals with nonmetals;

Metallic based on electron pooling: metals with metals.

Ionic, covalent, metallic:

Gilbert Newton Lewis (1875-1946), American scientist

The octet rule:

when atoms bond, they lose, gain, or share electrons to attain a filled outer

level of eight (or two) electrons.

Let us build Lewis electron-dot symbols for atoms:

Si F

Let us build a Lewis electron-dot symbol for an ion:

Br-

What Lewis electron-dot symbols say:

For a metal, the total number of dots is the maximum number of electrons an atom loses to form a cation;

For a nonmetal, the number of unpaired dots is the number of electrons that become paired either through electron gain or through electron sharing.

The central ideaof the ionic bonding model

is the transfer of electrons from metal atoms to nonmetal atoms to form ions

that come together in a solid ionic compound.

Three ways to represent formation of a chemical bond (electron transfer):

Electron configurations;

Electron orbitals;

Lewis electron-dot symbols.

A sample problem

on depicting ion formation.

Ionic compounds occur

just because of the enormous release of energy when the ions come together

and form the solid.

Surprisingly,

electron-transfer process by itself actually absorbs energy.

Ionic compounds exist

only because the lattice energy exceeds the energetically unfavorable

electron transfer.

Ionic compounds are

hard;

rigid;

brittle.

Why?

THE END