Untitled - Kelly Walsh High School

128 CHEMISTRY FOR THE UTTERLY CONFUSED
Get Started
9-1 Lewis Symbols
Don’t Forget!
Don’t Forget!
The goal of this chapter is to help you gain an understanding of Lewis structures.
These are necessary to study chemical bonding, both ionic and covalent. You
might need to review the Section 2-3 on chemical formulas. Chapter 6 on Hess’s
law may also be helpful. Ionization energies and electron affinities, from Chapter 8,
are also important. And remember: the only way to master this material is to
Practice, Practice, Practice.
Chemical compounds are pure substances composed of atoms in specific ratios
held together by chemical bonds. The basic principle that governs bonding is
the observed stability of the noble gas family (group VIIIA or group 18 elements).
Their extreme stability is related to the fact that they have a filled
valence shell. For all noble gases, except helium, this is a full complement of
8 valence electrons. This is the basis for the octet rule. During chemical reactions,
atoms tend to gain, lose, or share electrons in order to achieve an octet of
electrons in their outer shell. By this process, the elements become isoelectronic
with the closest noble gas. Isoelectronic means that the species have the same
number and arrangement of electrons. There are exceptions to the octet rule,
but most of the time it applies.
The octet rule doesn’t always work, but for the representative elements, it works
a majority of the time.
Here, as in most cases, hydrogen is an exception. Hydrogen achieves stability
with a pair instead of an octet.