Chemistry Stack Exchange is a question and answer site for scientists, academics, teachers, and students in the field of chemistry. It only takes a minute to sign up.
Sign up to join this community
I am having trouble understanding how valence electrons are counted in Helium.
My references are:
How many valence electrons does helium have?
Helium has two electrons in total, and according to the aufbau principle, it adopts the electronic configuration $\mathrm{1s^2}$. This means it has two electrons in s orbitals with a principal quantum number of 1.
The last (and only) level of helium's electronic configuration is $\mathrm{1s^2}$, and therefore $\ce{He}$ has 2 valence electrons.
Valence electrons are electrons in the outermost shell of an atom
Valency is the number of electrons involved in the formation of a chemical bond
The number of valence electrons of helium is 2 because of its configuration which is $1s^2$
Hovewer, the valency is 0 because it is already stable and none of the outermost electrons are involved in the formation of chemical bonds.
The outermost shell of an atom can accomodate a max of 8 electrons. It was observed that the atoms of elements,having a completely filled outermost shell show little chemical activity. In other words their combining capacity is 0. Of these inert elements, the helium atom has 2 electrons in its outermost shell and all other elements have atoms with 8 electrons in the outermost shell. Their combining capacity of the atoms of other elements,that is their tendency to react & form molecules with same or different elements,was thus explained as an attempt to attain a fully-filled outermost shell.
