valencies

[evolution]

the valency of an element is the number of electrons it must lose or gain before it has a full outer shell.
In the periodic table the valency of the elements in group 1 is 1, group 2 is 2, group 3 is 3 and so on.
Electron arrangement: 2 electrons in the first shell and eight electrons in each shell thereafter.

so..........if caesium is in group 1 it has a valency of 1. However it's atomic number is 55 therefore it has 55 electrons. 2 in the first shell, 8 in the 2nd, 8 in the 3rd, 8 in the 4th, 8 in the 5th, 8 in the 6th, 8 in the 7th leaving 5 in the outer shell. It would appear then that it needs to gain 3 electrons to achieve stability so it's valency should be 3 not 1???

[brachiopod]

The electron levels are sub-divided into s,p,d and f orbitals. There are only s obitals in the 1st level, s and p orbitals in the 2nd; s,p & d in the 3rd; and s,p,d and f in the 4th and subsequent levels.

s,p and d orbitals can hold 2,6 and 10 electrons respectively.

Thus for the 55 electrons of caesium, they are arranged;

 

1st level 2 x s electrons

2nd level 2 x s elctrons

             6 x p electrons

3rd level - 2 x s

              6 x p

             10 x d

4th level - 2 x s

              6 x p

            10 x d

The next electrons go into the 5s and 5p orbitals, as they are at a lower energy state than the 4f, hence;

5th level - 2 x s

              6 x p

And for the same reason, the last electron goes into the 6s level;

6th level 1 x s

This is your unpaired valency electron for a Group I metal. (And where I hope it all adds up to 55 !!)

 

[AllYourBase]

If I recall, this is one of those areas where GCSE science simplifies things, in order to avoid being bogged down, but the reality is that the issue is much more complex, which is discovered at A Level and at degree stage. I recall being quite surprised when I started my Chemistry degree.

[helghast]

the number of electrons in each shell is n squared times 2 where n is the shell number therfore it goes 2 8 18 32 50 etc

[magicdice]

electrons aren't actually feasible

 

all the theories are fudged slightly to indicate that there really is an electron, but even factoring in the quantum physics of it, the electron would still inevitably spiral into the nucleus. so it can't exist in practice