How to find valence electrons of an element

[Katie Le 3K]

sorry if this is dumb but in Prof Lavelle's lecture, he was drawing a picture of the Lewis structure of Cl and said " we know that cl has 7 valence electrons" and then drew dots. but like how do i find out the valence electrons of cl? am i supposed to memorize it?

[TrishaP_3E]

Because the amount of valence electrons is usually just the amount of electrons in the outer shell, you count all of the electrons that would be under the highest n value the atom has. I find it easier to just look at the row at which the element is on, and count the number of columns there are before it, and including it, and that's how many valence electrons there are.

For example, Cl- falls on the 7th column of its row of the periodic table, and therefore has 7 valence e-.

Hope this helps!

[SophiaJenny3I]

Hi! So you just look at the group numbers on the periodic table. So, chlorine is in group 17, so it has 7 valence electrons. Oxygen is in group 16, and thus has 6 valence electrons. You avoid the transition metals using this method. Lithium is in group 1, and thus has 1 valence electron. When you are on the right side of the transition metals, you subtract ten from the group number to get the valence electron. When you are on the left side, it is just the group number.

[Abril Guanes 2A]

I found this table that helps visualize it a little bit more clearly. I hope this helps!

[Isaac Wen]

It definitely helps to memorize them (honestly if you do a few problems, you'll remember it pretty easily). Note that the elements on the right side of the transition metals are missing fewer valence electrons to form a complete shell so they tend to gain electrons. The opposite can be said about elements on the left side. Noble gases are the exception because their valence electrons completely fill up the outermost shell.

[BaileyB1F]

This question may also be something that Professor Lavelle already said or something that I should already know, but I was wondering why the transition metals in the middle of the periodic table don't have any tabled number of valence electrons like how we can tell the valence electrons of the other elements based on their group number.

[805593945]

It really depends on the group, except for the transition metals. I think the people who came before me explained it pretty well but it also takes a while to remember.