Bonding in Compounds

Question

How can you ID different types of bonds in a compound? I mean how can one tell if something is covalently bonded, for example CH3OH? I see that it can hydrogen bond (O with the H), but can't see the co-valence in it even though its there.

Answer 1

Looking at a good table of electronegativities will tell you the electron affinity of each element.  The definitions differ slightly between books, but off the top of my head non-polar covalent bonds have an electronegativity difference of 0-0.9, polar covalent have a diifference of 1-1.9 and ionic bonds have a difference greater of 2 or greater. You should double check these values.

So in methanol, CH3OH the structure is:

3H-C-O

The electronegativity difference between carbon and hydrogen is 0.4, so these are nonpolar covalently bonded.  The diff between carbon is oxygen see is 1.

Answer 2

You can identify covalent bonds in a compound. If it is an ionic compound, you will have a positive and a negative ion. You can''t just 'see' the bonds between two elements in a compound, you need to work out the structural formula, like draw a dot and cross diagram or something. You will know there is covalent or dative bonding when all the elements are non-metals, but exceptions are ammonium chloride which has both covalent and ionic bonding in it. You could have written the formula of CH3OH as CH4O or something right, but the formula tells something about the structure.the covalent bonding is here between CH3 and OH.

Answer 3

The general rule is that a non-metal bonds with another non-metal via covalent bonds (sharing of electrons).

Metals bond with non-metals via ionic bonding (electrostatic attraction between two oppositely charged ions).

For your example above, all the bonds are covalent bonds as all bonds are between non-metals, including the O-H bond.

For something like NaCl it is obviously ionic, as it is a metal with a non-metal.

Then you have things called polyatomic ions. These are ions that have more then one type of non-metal atom covalently bound in a combination that results in the molecule having a charge.

For example (SO4)^2-, (OH)^-, (NH4)^+. The bonding within these polyatomic ions is covalent, but the entire thing is an ion. They will form ionic compounds with oppositely charged ions.

eg. CaSO4, NaOH, NH4Cl.

If you reacted your CH3OH with Na you would get CH3ONa. This is an ionic compound, with two species present.

(CH3O)^-, which is polyatomic ion and    Na^+

Hydrogen bonding is not a part of the formation of molecules, rather it is a strong attraction between an O (or N or F) in one molecule and a Hydrogen attached to an O (or N or F) of a different molecule. This comes about because the polarity of an H-F, H-O, or H-N bond is extremely high. In these bonds the electrons are pulled strongly toward the electronegative (O,N,F) atoms, leaving the H as essentially +ve, thus it is strongly attracted to O, N, F in other molecules.