Pirate Chemistry
Covalent Bonding
We spent our last unit investigating what happens when metals bond with non-metals. We
learned that metals tend to give up electrons and become positively charged while non-metals
take those electrons to become negatively charged. These oppositely charged particles then attract in three dimensions to make crystal lattices of varying shapes and strengths. This was ionic bonding.
The whole point of ionic bonding was for the individual atoms to achieve a stable electron configuration by losing or gaining electrons. But is there any other way that atoms can achieve stability?
Let me give you an analogy. My daughters collect various toys like My Little Ponies. My first
daughter Madison has 7 ponies in her collection. My second daughter Valerie also has 7 ponies. Madison needs one pony from Val’s collection to make a complete set. Similarly, Val
needs one of Maddie’s for completion. Neither one wants to give up any of their ponies so after
much begging, pleading, fighting, crying, and negotiating, they agree to share the pony the other needs to complete their set. Ownership is now “joint” between them and both can say they
have complete sets of dolls and much to the relief of Dad, the fighting stops.
What does this have to do with chemistry? Atoms become stable (get a complete set of ponies)
when they have a full valence shell of electrons. Instead of gaining or losing electrons in an
ionic bond as above, it is possible for some atoms to share their electrons with others to achieve
stability. This can only occur with non-metals, however. Remember that non-metals want to
gain electrons from other atoms. Thus they can attempt to take electrons from other non-metals
and in the process share those electrons. Metals want to give their electrons away. Consequently, they rarely share their electrons so can only be involved in ionic bonding.
Ionic bonding:
Covalent bonding:
metals and non-metals must be present
only non-metals can be present
Let’s look at an example:
F
An atom of fluorine has 9 total electrons.
Two of them are in the first shell which is
complete. Seven of them are in the second
shell which needs just one more electron to
be complete.
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Pirate Chemistry
F
F
Two different fluorine atoms each need one more electron to become stable. Instead of taking
an electron from one and giving to another, the fluorine atoms overlap and share one of their
electrons:
F
F
Now each fluorine atom has two electrons in their first shell and 8 electrons in their second
shell. They have shared their valence electrons to create a covalent bond– a chemical link between two atoms that share their electrons to become stable.
All text copyright Chris Smith 2009. All pictures obtained from internet and are copyright of their owners but assumed to be public accessible. If you are the owner of a picture and want it removed, email csmith@d211.org
Pirate Chemistry
Before we go on, though, let’s make our life easier. Atoms can get very big very fast in these
examples and we want to simplify things as much as possible. Consequently, we can ignore
most of the electrons in an atom as being unimportant for bonding purposes. For example:
Cl
This looks complicated.
An atom of chlorine has 17 total electrons: 2 in the first shell, 8 in the second shell, and 7 in the
third shell. We don’t need to focus on most of those electrons because they occupy shells that
are filled. The first shell is filled with its 2 electrons and the second shell is filled with 8; these
shells are filled and stable. Let’s just ignore them and focus only on the electrons in the outer
or valence shell.
Cl
This looks much easier!
This certainly looks a lot simpler now! Following this idea, we only need to recognize that the
number of valence electrons in an atom is going to be the column number that it is in:
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Pirate Chemistry
1A
H
Notice that in each column, the number of valence electrons is equal to the column number.
Boron is in column 3 and has three “dots” which represent valence electrons. Oxygen and sulfur are in column 6 and have 6 valence electrons. We are ignoring the transition metals because
their chemistry is far more complicated and we will be focusing only on the non-metals anyway.
Now that we know how many valence electrons these atoms have, we can figure out how to put
them together into covalent compounds!
All text copyright Chris Smith 2009. All pictures obtained from internet and are copyright of their owners but assumed to be public accessible. If you are the owner of a picture and want it removed, email csmith@d211.org
Pirate Chemistry
Questions
1. What do atoms do with electrons in a covalent bond?
2. What kind of atoms are involved in an ionic bond; only metals, only non-metals, or must
both be present?
3. What kind of atoms are involved in a covalent bond; only metals, only non-metals, or must
both be present?
4. Why can we ignore the electrons on inner shells of an atom?
5. What are valence electrons?
6. How many valence electrons does each of the following atoms have:
A. Oxygen
B. Bromine
C. Boron
D. Selenium
E. Fluorine
F. Carbon
G. Silicon
H. Nitrogen
I. Iodine
J. Chlorine
All text copyright Chris Smith 2009. All pictures obtained from internet and are copyright of their owners but assumed to be public accessible. If you are the owner of a picture and want it removed, email csmith@d211.org