Expert: Walter Hintz - 6/1/2006

Question
Why are the ratios of elements in molecular formulas always fixed, H2O instead of H5O? and CH4 instead of CH6? in terms of the atoms making up the molecules?

Answer
Hi corie-ann;
This is a good question and one that I often get from my students. Chemical language is a lot like spelling.
First all all keep in mind that the chemical language that we use( the formuli) is our way of observing what conditions actually exist and they are the way they are because of the laws not only of chemistry but of physics as well. Compounds are held together by forces and these forces determine the configuration. H2O exists but H5O does not because there is no way 5 hydrogens can combine with 1 Oxygen.  CH6 can not occur since Carbon has only 4 bonding sites. 1 C can only hold 4 h.  CH 4 is methane gas. C2H6 does occur however.