How do I determine the valency of a main group element?

Question

Olivia Anton · Accepted Answer

Usually by looking at how many columns away from the noble gases the element is, on the periodic table.

The valency is basically how many bonds it can make, which you can find by drawing the Lewis dot structure and finding which electrons are unpaired at the moment.

Take oxygen (#"O"#) for example (atomic number #8#), which has #bb(6)# valence electrons (two #2s# and four #2p# electrons), because it is #bb(2)# columns away from the noble gases (#8 - 2 = 6#).

Drawing in the valence electrons one by one, the first four can be drawn like this:

#cdot stackrel(.)("O")cdot#
#color(white)(.')""^(.)#

Drawing the remaining two, it doesn't really matter where you place them; you'll find that there are two unpaired electrons when you're done:

#cdot stackrel(..)("O"):#
#color(white)(a.)""^(.)#

Or, maybe you could have:

#cdot stackrel(..)("O")cdot#
#color(white)('')""^(..)#

Either way, the Lewis structure tells us that the valency of oxygen atom is #2#, so it can make #bb(2)# bonds via electron sharing.

Again, these covalent bonds are made by pairing up each electron with another electron from the other atom, such as carbon or hydrogen.

Two examples are water:

or even something like formaldehyde:

in which it also makes #bb(2)# bonds (they are to the same atom, but there are still the same two electrons shared with carbon).

As a result, you typically see oxygen making two bonds; otherwise, it ends to have a charge, like in #"OH"^(-)# (hydroxide), or #"H"_3"O"^(+)# (hydronium).

Cooper Anderson · Answer

undefined The valency of a main group element can be determined by looking at its group number on the periodic table. For main group elements, the valency corresponds to the group number. For example, Group 1 elements have a valency of 1, Group 2 elements have a valency of 2, Group 13 elements have a valency of 3, and so on. However, there are exceptions like transition metals, which have variable valencies.

Axel Alvarado · Answer

undefined The valency of a main group element can be determined by examining its group number on the periodic table. For main group elements (also known as representative elements), the group number indicates the number of valence electrons they have.

Group 1 elements have 1 valence electron, Group 2 elements have 2 valence electrons, Group 13 elements have 3 valence electrons, Group 14 elements have 4 valence electrons, Group 15 elements have 5 valence electrons, Group 16 elements have 6 valence electrons, Group 17 elements have 7 valence electrons, and Group 18 elements (Noble gases) have 8 valence electrons except for helium, which has only 2 valence electrons.

The valency of a main group element is typically equal to the number of valence electrons it needs to gain or lose to achieve a stable electron configuration, usually the nearest noble gas configuration.