Lecture01222

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Information about Lecture01222

Published on July 21, 2008

Author: uladzimir

Source: slideshare.net

Description

a supplemental resource for students

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 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

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.

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 idea of 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.

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?

hard;

rigid;

brittle.

Why?

THE END

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