how to use the periodic table to determine the number of electrons available for bonding?

Question

How to use the Periodic Table to determine the number of electrons and be able to teach a group of kids to understand it?

Answer 1

I explain to my students that columns 4A-7A are 'wanna be' noble gases, ie want 8 valence e- (except for first period since only need 2 e-).

The elements are listed in columns and each of the A columns gives the number of valence electrons. Transition metals of course don't follow the same rules, so just talk about columns 1A-8A.

The atoms in columns 1A-4A can only make as many bonds as they have valence electrons, obviously.

I use molecule kits, but if you don't have them, use toothpicks and clay/playdough or have the kids make Bohr models on paper of one of the atoms in each column and they can see how many bonds can be formed.

Answer 2

If I remember my High School chemistry right, it depends which column the element is in. For example, Hydrogen is in column 1 so it has 1 electron for bonding. Carbon is in the 4th so it has 4 atoms for bonding (that's why a diamond has so much strength because it has 4 bonds on each atom)
So, up to the 4th column, the elements contribute one electron to the bond for each column number.
After the 4th column, the elements absorb electrons for the bond. To understnad this, you subtract from 8 to get the number of bonding electrons it will receive. (Example, Oxygen is in the 6th column, so it has 8-6=2 available for bonding. That is why you have H2O for water....two Hydrogen each contribute one electron and the Oxygen receives two electrons.)

The column number dictates how many electrons are in the outer shell of electrons, or the "valence" electrons. An atom always wants to have 8 where it is stable. So it will bond easily to an element that has a compatible number of valence electrons. (For example, NaCl - Sodium Chloride or regular salt, is stable because the Sodium contributes one to the Chlorine so they both think that they have 8 in their outer shell.)

The elements on the far right (column 8 - called the noble gases) don't contribute or absorb electrons under normal circumstances so they don't normally bond.

There might be some exceptions to this rule, but I think it's good enough for school.

The above rule works OK for elements 1-20 and the others in those columns, but I can't remember how to explain the elements in the middle (the "B" series ones starting with element 21 called the Transition Metals). They have variable valences and I hope somebody else helps with this one.

Now, the hard part....explaining it to school kids.
Maybe what I said above is good enough?

Answer 3

It depends on the element(s) involved, with the number limited by the number of electrons in the valence orbitals.