How are radical valencies solved?

[BigMoosie]

How do we work out the valencies of such radicals as [math]SO_4[/math]? Do most compounds have valencies or just radicals? I always thought that for something to have a valency it would have a desire to gain or lose electrons, I cant see how a compound would do that... it just doesnt seem to make sence, once it is a compound it should be satisfied.

 

Hope somebody can help me clear this up.

[woelen]

How do we work out the valencies of such radicals as [math]SO_4[/math]? Do most compounds have valencies or just radicals? I always thought that for something to have a valency it would have a desire to gain or lose electrons' date=' I cant see how a compound would do that... it just doesnt seem to make sence, once it is a compound it should be satisfied.

 

Hope somebody can help me clear this up.[/quote']

 

If you really want to understand, then have a look at the concept of molecular orbitals.

 

In single atoms, electrons are in atomic orbitals (in laymans terms, something resembling orbits, but a good description can only be given by means of quantum mechanics), but when atoms combine to molecules, then part of the electrons are shared between atoms and they 'orbit' around over the whole molecule (better: they are distributed over the whole molecule). Molecules (or ions, or in fact any structure consisting of multiple boonded atoms) can certainly have a desire of electrons or want to get rid of electrons.

 

An example is the following compounds:

 

hydroxyl: OH This is a very strong oxidizer and really wants an electron. If it gains an electron it is changed to the the stable hydroxide and the newly gained electron is distributed over the whole OH(-) ion. So, one could formally speak of hydroxyl having valence 1, because it can make a single bond with something else. In practice, however, the valency concept is not used for compounds, but for atoms only.

 

In general, the innermost atoms are confined to the atom to which they belong, but the outermost electrons are distributed over molecules or part of molecules. A very nice example is the benzene molecule C6H6. This has 6 electrons, which are distributed over all 6 C-atoms and one cannot say anymore which electron belongs to which atom. Other electrons are confined to just two C-atoms or one C-atom and a H-atom.

[woelen]

How do we work out the valencies of such radicals as [math]SO_4[/math]? Do most compounds have valencies or just radicals? I always thought that for something to have a valency it would have a desire to gain or lose electrons' date=' I cant see how a compound would do that... it just doesnt seem to make sence, once it is a compound it should be satisfied.

 

Hope somebody can help me clear this up.[/quote']

I just forgot something in my previous post. A radical also is a compound and it frequently also is a molecule. A radical is not that special. A compound is called a radical, if it has an odd electronic configuration. A well-known compound, such as the brown NO2 gas or the deep yellow ClO2 gas also is called a radical, while these molecules are stable enough to be prepared in macroscopic quantities and can be stored. In fact, I have made both gases in my home lab several times

 

As a rule of thumb, you can assume, however, that radicals are very reactive compounds. A known ionic radical is the ion SO4(-). This can be prepared in minute quantities when a solution of a sulfate is electrolysed. Two ions SO4(-) can combine to the well-known peroxodisulfate ion S2O8(2-). So, where would you place the border between radical, compound and molecule?

[BigMoosie]

This is very interesting, thankyou for your knowledge woelen. These insights have sparked several other questions I am pondering. Is it possible for something to have a valency of between two integers [eg 0.5+] or do we just say it is a particularly unreactive particle of valency 1 ?

 

More Q but midnight here, cya tomorrow!

[woelen]

This is very interesting' date=' thankyou for your knowledge woelen. These insights have sparked several other questions I am pondering. Is it possible for something to have a valency of between two integers [eg 0.5+'] or do we just say it is a particularly unreactive particle of valency 1 ?

 

More Q but midnight here, cya tomorrow!

From this, I understand that you relate valency to reactiveness. You mean that the higher the valency, the higher the reactiveness?

 

The fact is that valency is not related to reactiveness. The element fluorine has valency 1 and has no other possibilities. Yet, it is the most reactive element there is and also among the compounds (which is a much broader class) it is among the most reactive ones. On the other hand, an element as sulphur frequently has valency 2, but it is not really reactive.

 

The concept of fractional valency I have never seen. Remember, the concept of valency is introduced to make reasoning about chemical compounds and bonds somewhat easier, but with many real-life molecules this concept gets flawed and more advanced concepts like molecular orbitals or even low-level quantum mechanics is needed in order to understand the structure of the compound.

[akcapr]

so valency is the # of electrons on the valence shell

[woelen]

so valency is the # of electrons on the valence shell

What is the valence shell? This concept works quite OK for e.g. sodium, chlorine, etc. For transition metals it does not work anymore. Many transition metals use electrons from their outer shell, but also from deeper shells in their chemical reactions.

For the lantanides things get even more complex. With these, the second deepest shell also is involved in the chemistry of the elements, so one cannot simply speak of THE valence shell. As I stated already, for these elements, the only way to understand how it is is by performing mathematical simulations of quantum mechanical models.

[Mendelejev]

A radical is not that special. A compound is called a radical, if it has an odd electronic configuration.

 

Yes, indeed. So one half of all the elements we can collect are radicals. Chlorine for example, has a valency of zeven, so 3 pairs of two electrons and 1 apart, the radical.

[jdurg]

However, chlorine exists as a diatomic molecule, as does Hydrogen, Nitrogen, Oxygen, and all of the halogens. Therefore, you never truly have them as a radical since their diatomic nature removes that 'odd number' of electrons.

[akcapr]

ahaha i see. but in compounds i guess u could consider those halogens as having radicals, (kinda, not really tho)

[woelen]

ahaha i see. but in compounds i guess u could consider those halogens as having radicals, (kinda, not really tho)

You cannot say that a certain atom (e.g. the halogen) has a radical, a compound or ion as a whole is a radical (or not).

 

For the halogens, the compound ClO2 is regarded a radical, but Cl2O is not. Try to draw a Lewis structure of ClO2 and you'll see that you have trouble making such a model, while it can be done easily for Cl2O. The same difficulty exists for NO2 and NO, but not for N2O5, N2O3 and NO3(-).