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I want an high-school level answer. What I mean with "valence electrons" is the outermost electrons in that atoms' electronic arrangement? For example, 3 in an atom with an electronic arrangement of 2, 8, 3.)

Without actually writing the electron configuration, or orbitals, and knowing electron number, is there any way to find this number easily?

Also, is there an easy way to find if certain atom fits "atomic/orbital symmetry" given the numbers of electrons? (I don't know the english words for this and couldn't find them. So I translated it literally, but what I mean is, if orbital is half-full or full i.e $\mathrm{s^1}$ or $\mathrm{2p^3}$ or $\mathrm{2p^6}$ and so on... hope you understand what I am trying to say)

I am asking this because sometimes questions give me electron numbers in a range of 40+ and just writing it out doesn't seem like a good way.

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You can get the valence electrons in an atom's electronic arrangement by consulting the periodic table:

enter image description here

  • The Group 1 atoms have 1 valence electron.
  • The Group 2 atoms have 2 valence electrons.
  • The Group 3 atoms have 3 valence electrons.
  • The Group 4 atoms have 4 valence electrons.
  • The Group 5 atoms have 5 valence electrons.
  • The Group 6 atoms have 6 valence electrons.
  • The Group 7 atoms have 7 valence electrons.

The atom with electric configuration 2, 8, 3 is Aluminium and you can find it in Group 3 of the periodic table.

The periodic table is usually given in exams so...

The first two groups of the periodic table are the groups concerned with the filling of the $s$ orbital. So, all Group 1 atoms will have an outermost $s$ orbital filled with a single electron.

Similarly, Group 3 - Group 8 (Group 8 is also referred to as Group 0) are where the $p$ orbital is being filled up. All the Group 5 atoms thus all have an outermost $p$ orbital filled with 3 electrons.

The Periods in the periodic table can be used as an indication of the number of shells the atom has. Sulfur for instance is in Period 3 and thus has 3 shells.

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  • $\begingroup$ periodic table isnt given in exams here. second part of your answer is really helpful for me, thx for that :) but about first part, I cant really know the group number without writing down electron configs can I ? is there a way to do this without going -2 -8 or 1s1 1s2 was what I was asking $\endgroup$ – user4117 Jan 6 '14 at 7:34
  • $\begingroup$ @user4117 Well, that's an unusual case... If your exams aren't too soon, I would suggest using your periodic table as much as possible. This way, it will start getting in your memory ;) Otherwise, there's no really any other way to go about this (besides just remembering it), unfortunately :( $\endgroup$ – Jerry Jan 6 '14 at 7:37
  • $\begingroup$ @answerer The table you put in contradicts your whole statement! e.g. the table clearly puts aluminium in group 13 and not 3! $\endgroup$ – Nihilist_Frost Oct 14 '15 at 4:25
  • $\begingroup$ @Nihilist_Frost The number you are looking at is the column number, not the group number. $\endgroup$ – Jerry Oct 14 '15 at 9:34
  • $\begingroup$ Also, the picture I had was simpler, with less stuff to confuse. I don't know how the link got broken. I'll try find a simpler one that the one above. $\endgroup$ – Jerry Oct 14 '15 at 9:36
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Yes there is! For all elements in the following groups;

Group 1A= +1 Group 2A= +2 Group 3A= +3 Group 4A= +4 or -4 Group 5A= -3

From group 5, the valency descends in this order;

-3, -2, -1, 0.

Group 8A elements have a valency of Zero.

I hate complicated stuff too lol.

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    $\begingroup$ I think that's oxidation state, not valency. $\endgroup$ – pentavalentcarbon Jun 5 '17 at 23:12

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