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the free encyclopedia.
A diagram of several simple
Lewis structures of
molecules and atoms.
The Lewis Structure was named
after
G.N. Lewis. In
chemistry, a Lewis
structure is a 2D
representation of a
molecule on paper. It is used
primarily to show the approximate
relative positions of each
atom in relation to the other
atoms in the molecule, the
topology of the
covalent bonds linking them,
and the allocation of
electrons to the atoms in the
molecule.
There are a number of
simplified Lewis structures. In
organic chemistry, rather than
drawing every single atomic
symbol, simple lines are used.
Essentially, at every "bend" in
the line, there is assumed to be a
saturated carbon (CH2), and
the end of every line is a
saturated carbon (CH3). This often
saves quite a bit of time. For a
few examples:
propane, which is a simple
three carbon chain, would be a
simple zig-zag line, with two line
segments;
cyclohexane, which is a
hexagonal ring of carbons, would
be drawn simply as a hexagon.
Lewis structures only deal with
the valence electrons of the atom
in question. The valence electrons
are the ones in the outer orbitals
that interact with the valence
electrons of other atoms to form
molecular bonds. Valence electrons
in the s orbital are shown as dots
to the right of the element's
name. Electrons in each of the
three p orbitals are shown above,
to the left of, and below the
element's name.
When Lewis structures are used
in the display of the form of
molecules, each molecular bond
(not each shared electron, as some
may think; each molecular bond
contains two shared electrons) is
represented by a line. The Noble
Gases do not form bonds because
they have a full
octet.
A number of rules (based mostly
on the
octet rule and the
duet rule) can be applied to
work out the distribution of
charge across the structure. This
does not always produce correct
results, but works in enough cases
to make Lewis structures a useful
tool in chemistry. Limitations of
Lewis structural representations
are overcome partly by
incorporation of other forms of
notation, for example
resonance structures.
How to Draw a Lewis Structure
The lewis structure for H2O,
1.) Count the valence electrons
in H20.
1 for each H, 6 for O
1 + 1 + 6 = 8
2.) Use a pair of electrons for
each bond.
H--O--H
3.) Use the remaining electrons
to fullfil the octet rule and the
duet rule for H.
References
