Question

how to know valence of arsenic and how​

Answer 1

Answer:

Ground state, neutral arsenic atoms have five valence electrons.

Refer to the explanation.

Explanation:

For the representative elements, groups 1,2, and 13-18 (IA-VIIIA), the number of valence electrons in their atoms can be determined from their group number. For groups 1 and 2, the group number is the number of valence electrons. For groups 13-18, the number of valence electrons is 10 minus the group number. For the A groups, the group number is the number of valence electrons.

Arsenic is in group 15, so its atoms have 5 valence electrons.

We can also determine the number of valence electrons of the representative elements by determining their ground state electron configurations. The highest energy (outermost) s and p sublevels, also called the valence shell, contain the valence electrons.

Arsenic has atomic number 33. This means arsenic atoms have 33 protons and, if neutral, 33 electrons. The electron configuration for a ground state, neutral arsenic atom is:

1s^2  2s^2  2p^6  3s^2  3p^6  3d^10  4s^2  4p^3

or  

[Ar]  3d^10  4s^2  4p^3

So we can see that the electron configuration for arsenic has 5 electrons in the valence shell of the 4th energy level.