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Lecture

CHEM 1000 Lecture Notes - Chemical Polarity, Covalent Bond, Ionic Bonding


Department
Chemistry
Course Code
CHEM 1000
Professor
William Pietro

Page:
of 17
•1
CHEM 1000A 3.0 Chemical Bonding I 1
Chemical Bonding
Petrucci, Harwood and Herring: Chapters 11 and 12
•Aims:
To look at bonding and possible shapes of
molecules
We will mainly do this through Lewis structures
To look at ionic and covalent bonds
Use valence shell electronic structure to predict
shapes of molecules
CHEM 1000A 3.0 Chemical Bonding I 2
Chemical Bonding
The most important concepts here are:
Electrons, particularly valence electrons play a
fundamental role in chemical bonding.
When elements combine to produce compounds
they are attempting to achieve a valence shell
like a noble gas
•2
CHEM 1000A 3.0 Chemical Bonding I 3
Chemical Bonding
The driving force for the production of chemical
bonds is the need for an atom to complete a
valence shell (usually 8 electrons)
Often electrons can be transferred from one atom to
another to make ions. The atoms are then held together
by coulombic forces in an ionic bond
More often the only way an atom can gain electrons is
by sharing. This sharing produces a covalent bond
CHEM 1000A 3.0 Chemical Bonding I 4
Lewis Symbols
This is a way of representing the valence
electrons in an element
It does not include the inner shell electrons
It does not include the spin of an electron
e.g. Si ([Ne]3s23p2)
N ([He]2s22p3)
Si
N
•3
CHEM 1000A 3.0 Chemical Bonding I 5
Lewis Structures
These are the combination of Lewis
symbols that represents the sharing or
transfer of electrons in a molecule
–Examples
Ionic bond
Covalent bond
Na + Cl [Na]+ [ Cl ]-
xx
H + Cl H Cl
xx
CHEM 1000A 3.0 Chemical Bonding I 6
Ionic Compounds
We don’t usually see isolated ionic compounds
Normally they are in crystals where one anion
(negative) is attached to several cations (positive)
and vice versa. Electrical neutrality means the total
number of each ion is the same.