A Lewis structure is a way of representing the nature of the bonding in a molecule or ion. These show how many of the valence electrons on that species are bonding and how many are nonbonding. Lewis structures are very useful in predicting both reactivity and shape.
How do I know how many valence electrons are available on the atoms involved in bonding?
The number of valence electrons for an atom is equal to the last digit of its Group Number in the Periodic Table.
The number of valence electrons on a molecule is the sum of the valence electrons on all of its atoms.
How can I draw a Lewis structure?
Before introducing the rules for drawing Lewis structures, it is important to understand what a given Lewis structure means. Consider the Lewis structure for the molecule H2O.
Four of the eight electrons are in single bonds (each line represents a bonding electron pair) and four are in nonbonding electron pairs at oxygen (a double dot represents a nonbonding electron pair).
How do I know how many valence electrons are available on the atoms involved in bonding?
| Element | Group Number | Valence electrons |
| carbon | 14 | 4 |
| bromine | 17 | 7 |
| CBr4 has 4(C) + 28(4Br) = 32 | ||
The number of valence electrons for an atom is equal to the last digit of its Group Number in the Periodic Table.
The number of valence electrons on a molecule is the sum of the valence electrons on all of its atoms.
How can I draw a Lewis structure?
Before introducing the rules for drawing Lewis structures, it is important to understand what a given Lewis structure means. Consider the Lewis structure for the molecule H2O.
| 2 H | 2 electrons |
| 1 O (Group 16) | 6 electrons |
| total electrons available | 8 electrons |
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Four of the eight electrons are in single bonds (each line represents a bonding electron pair) and four are in nonbonding electron pairs at oxygen (a double dot represents a nonbonding electron pair).