November 14, 2010

Lewis Structures of Some Common Compounds and Ions

It's been quite a while since my last post....

...and there's so much catching up to do!

And so without further ado, Chemistry Partner resumes to make your life in chemistry a little bit easier.

This current update serves as a supplement to my October 23, 2009 post, Drawing Lewis Electron Dot Structure or Formula.

It consists of illustrations of Lewis structures showing the covalent bonding of the following:

  1. Inorganic Compounds

    • NH3 (ammonia)

    • HNO3 (nitric acid)

    • SO3 (sulfur trioxide)

    • H2S (hydrogen sulfide)

    • N2 (nitrogen gas)

    • O3 (ozone)

    • H2SO4 (sulfuric acid)

    • H2O (water)

  2. Organic Compounds

    • HNCO (isocyanic acid)

    • CO (carbon monoxide)

    • HCN (hydrogen cyanide)

    • CH3COOH (acetic acid)

    • H2CO3 (hydrogen carbonate or carbonic acid)

  3. Polyatomic Ions

    • SO42- (sulfate ion)

    • NH4+ (ammonium ion)

    • PO43- (phosphate ion)

    • C2O42- (oxalate ion)

    • NO3- (nitrate ion)

    • CO42- (carbonate ion)

In order to identify each atom's respective valence electrons easily, different colors for atoms were used.

Also, red and grey shades were used to highlight the atoms with negative and positive formal charges.

Lewis Structures of Inorganic Compounds

Lewis electron-dot structures of NH3 and HNO3

Lewis electron-dot structures of SO3 and H2S

Where necessary, I used different colors for the same kind of atom. Here in the example of O3 (ozone) below, I used three different colors to distinguish the three different oxygen atoms.

For the structures of HNO3 (nitric acid) and SO3 (sulfur trioxide) above, the use of one color for the same kind of atom is enough to distinguish easily the individual atom's valence electrons.

For the rest of the illustrations below, you'll find the same methods of color assignment for the atoms.

Lewis electron-dot structures of N2 and O3

When more than one Lewis structures for a species are possible, the resonance structures are given as in the case of ozone, isocyanic acid, nitrate and carbonate ions.

For determining the most stable resonance structure(s) of a species, click here to see my earlier post about it.

Lewis electron-dot structures of H2SO4 and H2O

Lewis Structures of Organic Compounds

With the exception of hydrogen, you can see that an atom can share one or more of its valence electrons, with a maximum of six electrons shared between any two atoms.

Lewis electron-dot structures of HNCO

Lewis electron-dot structures of CO and HCN

Lewis electron-dot structures of CH3COOH and H2CO3

Lewis Structures of Ions

Here, the charge on a species is determined by either of the following:

  • the sum of all of the valence electrons of the atoms of the species minus the total number of electrons in the Lewis electron-dot structure of the species

  • the algebraic sum of all the formal charges of the species

For a discussion of the determination of the formal charges of atoms of a species, follow the link given above.

Lewis electron-dot structures of SO4 and NH4 ions

For some ions, just as the case is with the ammonium ion, the total number of electrons in its electron-dot structure is less than the total number of valence electrons of its atoms.

Referring to the ammonium ion above, it should have a total of 9 valence electrons (5 from N + 4x1 from H), but its electron-dot structure has only eight electrons.

Ammonia acts as Brönsted base, though a weak one, by accepting a proton thus forming ammonium ion. (See my article Solving Weak Acid/Base Dissociation Problems for a discussion of Brönsted acid-base reaction.)

Lewis electron-dot structures of PO4 and C2O4 ions

Lewis electron-dot structures of NO3 ion

And for some ions, the total number of electrons in its electron-dot structure is more than the total number of valence electrons of its atoms.

Observe that some oxygen atoms of the phosphate, oxalate, nitrate and carbonate ions have acquired electrons from atoms other than those its own atoms.

Lewis electron-dot structures of CO4 ion