Helium has 2 valence electrons.
We can write the valence electrons of helium using two different methods:
#1 Using periodic table
#2 Using electron configuration
Let’s break down each method in detail.
#1 Using Periodic Table
Get the periodic table having the chemical elements marked on it as mentioned above.
Now mark the location of helium on the periodic table.
Next, mark the group number of helium on the periodic table.
The valence electrons of each main group element can be determined by the column in which it is located.
(i.e., all group 1 elements have 1 valence electron, all group 2 elements have 2 valence electrons, skip the transition metals… then, all group 13 elements have 3 valence electrons, all group 14 elements have 4 valence electrons, and so on up to group 18 elements)
Helium is an exception that even if it lies in group 18, it has 2 valence electrons.
Question: Why does helium have 2 and not 8 valence electrons?
Answer: The atomic number of helium is 2, which means that there are 2 electrons around its nucleus. Now valence electrons are the electrons found in the atom’s outermost or valence shell. Helium has 2 electrons in its valence shell, so it has 2 valence electrons.
#2 Using Electron Configuration
- First, write electron configuration of helium
The electron configuration of helium is 1s2.
- Second, find highest energy level in electron configuration
In the above electron configuration, the highest energy level (1) is marked with green color.
- Finally, count electrons of that energy level
The 1st energy level contains 1s subshell and it has 2 electrons. So helium has a total of 2 valence electrons.
Next: Lithium Valence Electrons