The modern periodic table

[Dadface]

Hello.It seems that older periodic tables showed just eight groups but most modern periodic tables now show eighteen.Are there any reasons why eight used to be preferred and why eighteen is now chosen?I'm guessing that the change over is due to....well I don't know.Thanks for any answers.

[jedishrfu]

wikipedia has a discussion on it:

http://en.wikipedia.org/wiki/Periodic_table

The modern table uses QM to define the table structure based on shells and orbitals

the older tables used chemical properties to group elements falls along similar lines
but cant distinguish between orbital differences as seen in QM.

and if you look at the lanthanides and actinides they would expand the table horizontally giving quite a few more columns/groups than 18.

[Dadface]

Thank you jedishrfu
I think that the older tables are better in that they indicate more clearly how many electrons there are in the outer level.With the tables numbered one to eighteen one has to remember that for groups thirteen onwards it is the second digit only that gives the outer level electron number and one has to remember that the transition metals break the trend.
Having done some more searching I think I prefer those modern tables that label the groups previously labelled as one to eight(or zero) by use of 1A,11A etc.The labelling of the transition metals seems to be more interesting and at the moment I haven't a clue what information those labels are giving.I see,for example,that groups 8,9 and 10 are lumped together as group V111.
Anyway,I have been looking at periodic tables and for anybody who is interested may I recommend that you visit "NIST" and look at their table.It is the best I have seen so far.