Acetate ion contains carbon, hydrogen and oxygen atoms. Lewis structure of CH3COO- contains a negative charge on one oxygen atom. There is a double bond in CH3COO- lewis structure. Two stable resonance structures also can be drawn for acetate ion.
There is a double bond between carbon atom and one oxygen atom. Oxygen atom which has made a double bond with carbon atom has two lone pairs. Other oxygen atom has a -1 negative charge and three lone pairs.
Two resonance structures can be drawn for acetate ion.
When we draw a lewis structure, few guidelines are given. Number of steps can be changed according the complexity of the molecule or ion. Because acetate ion is a simple molecule, it is extremely easy to draw the lewis structure. However those all steps are mentioned and explained in detail in this tutorial for your knowledge.
There are three elements in acetate molecule; carbon, hydrogen and oxygen. Carbon is a group IVA element in the periodic table and contains four electrons in its last shell. Hydrogen, a group 1A element only has one electron and oxygen has six electrons in its last shell. Now, we can find out total number of electrons of the valance shells of acetate ion.
Because there is a -1 negative charge, an electron should be added to total number of electrons of the valance shells of acetate ion.
Total valance electrons pairs = σ bonds + π bonds + lone pairs at valence shells
Total electron pairs are determined by dividing the number total valence electrons by two. For, acetate ion, total pairs of electrons are twelve in their valence shells.
Skeletal of acetate ion is figured below. In a skeletal structure, atoms are only joint through single bonds and lone pairs are not marked.
After determining the skeletal of acetate ion, we can start to mark lone pairs on atoms. Remember that, there are total of twelve electron pairs.
There are +1 charge on carbon atom and -1 charge on each oxygen atom.
Because, there are charges in above structure, we should try to reduce charges to get the most stable structure if possible.
It is possible to convert one lone pair of oxygen atom to make a bond with carbon atom as following.
You can see now thee is only -1 charge on one oxygen atom. That means, this new structure is more stable than previous structure.