How many electrons does selenium have in its outermost electron shell? 

Answer:

Selenium  has six valence electrons in its outermost shell or energy level.

Explanation:

To find out the number of valence electrons in a selenium atom,we need to look at the periodic table.

The position of selenium in the periodic table  is in group VIA.For main group elements,valence electrons are equal to the group number.So,selenium atom has six valence electrons in its valence shell or outermost energy level.

Again, selenium is an element of group 16.Now just consider the unit place digit from group number.You are getting 6 which is equal to the number of valence electrons in selenium.

Here is the another way to find out the valence electrons of selenium.

The symbol of selenium is Se and the atomic number of arsenic is 34.So,it has thirty four electrons totally.

Now do the electronic configuration of selenium.

Se(34) =1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p4

             =[Ar] 3d10 4s2 4p4

[Tip: Complete filled d orbital is not considered as part of  valence shell or energy level]

The valence shell is the outermost shell and the electrons that are present in valence shell is called valence electrons.

The valence shell or energy level can be identified by the highest value of principal quantum number ,n.Here the highest value of n is 4.So,the valence shell is the 4th shell or energy level.

In 4th shell ,we get six valence electrons.So each selenium has six valence electrons in its outermost energy level or shell.

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