Question

how to determine the aspects for core and valence electrons in a periodic table. How comes in some elements like cobalt the 3d is on the valence side and arsenic the 3d is on the core side.​

Answer 1

See explanation

Step-by-step explanation:

The electron configuration of an atom in an element determines the property of the atom. The core electrons are found inside the atom while the valence electrons are found on the outermost shell of the atom.

For cobalt, the outermost shell electron configuration is; [Ar] 3d7 4s2. The 3d7 and 4s2 are found in the valence shell of cobalt.

For arsenic, the electronic configuration is [Ar] 3d¹⁰ 4s² 4p³. The valence electrons are 4s2, 4p3. The 3d electrons are found inside the arsenic atom.