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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