Using the periodic table, how can you tell how many valence ...

[geoffrey]

I have to draw a Lewis Dot Diagram and I don't know how.
I know that a Lewis Dot Diagram is the Atomic Symbol with dots representing the valence electrons.

Before, I knew the number of valence electrons according to the atomic number. First ring has maximum two and Second Ring has maximum eight. But I don't really know what to do when the atomic number gets really high.

I hear it has something to do with the groups? Was anything I said wrong?

[Celeste]

at the bottom of each box there is an electron configuration
it ususally looks something like this:
2-8-8-3
in this case, three is the number of valence electrons
you always find the last number, and that is your valence electrons
going down a group, each element has the same number of valence electrons

as for the lewis dot structure, you right the symbol of the element
you'd draw three dots around it, you go clockwise, starting at 12

if your element has more than four valence elcetrons, you just double up continuing clockwise

hope this helped! goodluck!

[Hungry!]

Ok, there is a patter, the first element of the period has 1 valence, then second element has two, the third has three, like this
Hydrogen has 1, helium 2, (next period)
Lithium 1, Beryllium 2, etc.

[Awilson837]

Well first of all you seem to know a good amount of what you are doing. When drawing the Lewis Dot Diagram you just follow the concept that  the first shell has 2 electrons and the second has 8 and the third has 8. If you are doing the diagram of Potassium, K, the atomic number is 19. Therefore you know its 2 on the 1st shell, 8 on the second shell and 8 on the third shell and the fourth shell can 8 as well but only 1 will be needed in this instance. So the electrical configuration is 2.8.8.1. It must always give you the atomic number that's the sure way that it is correct. 2+8+8+1= 19..i got the atomic number therefore my diagram is correct!!!! the number of electrons on the very last shell occupied by electrons is your valency number. In this case 1 is the valency number. The valency number is the number of the electrons on the outer shell that is available for sharing, being lost or gained by another element during bonding.

[hummingbird]

I assume that we are discussing atoms that are not ionized (in other words, the number of electrons is equal to the number of protons.

Valence electrons reside in the outer shell of the atom, so, those are the ones that are involved in absolutely all chemical reactions (the inner electrons don't seem to make much of a difference).

On the right side of the Periodic table, you will find noble gases (so called because they don't associate with other chemicals since they have filled (hence stable) valence shells).  Thus, Helium is not apt to chemically bond with other elements.  The chemicals are arranged so that atoms with just one electron in their valence shells are in vertical columns.  Similarly, atoms with two electrons, three electrons, etc. are grouped in vertical columns.

The heavier elements are at the bottom of the columns.  As electrons fill up one shell, another shell (at a higher energy level) is started.  

Thus, an atom with one electron in a lower valence shell has properties that are similar to a much heavier atom that has one electron in a higher valence shell.  The same can be said of an atom with two electrons in a lower valence shell compared to an atom with two electrons in a much higher energy valence shell (both in the same column of the Periodic Table, but one atom is heavier than the other).