Module 2 Intro

Module 2—Chemical Compounds

Explaining Molecular Formulas Using Lewis Symbols

 

Since valence electrons are involved in chemical bonding, Lewis symbols should be useful in explaining the changes that occur to atoms when they bond.

 

Molecular Elements

 

Seven elements are diatomic, including F2. How could Lewis symbols be used to represent a hydrogen molecule? Explain why this is a diatomic element.

 

Fluorine has seven valence electrons, requiring one more electron to complete its octet. You recall that atoms tend toward stability, meaning filled orbitals. Can you think of ways that a fluorine atom could complete its one unfilled orbital?

 

You may recall from your study in the previous module that metals often transfer electrons to non-metals, resulting in the formation of ions that have filled orbitals. Another possible association between atoms with unfilled orbitals is to share electrons. Two fluorine atoms could each obtain a stable octet of electrons if they shared a pair of electrons, forming a covalent bond.

 

 

This diagram explains why fluorine is diatomic.

 

What about oxygen?

 

An oxygen atom has six valence electrons. Sharing a pair of bonding electrons like fluorine would leave both oxygen atoms with seven valence electrons, which is less than a stable octet. The solution lies in having a double bond—the two oxygen atoms share two pairs of electrons at once like this:

 

 

 

Covalent bonds are represented by the pairs of electrons shown between the Lewis symbols. Covalent bonds can also be represented using a line to represent each shared pair of electrons. The result is a structural diagram. The structural diagram for fluorine (F2) would be written as F–F and for oxygen (O2) as O=O.

 

Self-Check

 

SC 6. Draw the molecular elements chlorine and bromine using Lewis symbols and structural diagrams.

 

 

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