The electrons present in the outermost shell of an atom or ion are known as valence electrons. In a chemical bond formation, only valence electrons of an atom take part.

The electrons present in the outermost shell of an atom or ion are known as valence electrons. In a chemical bond formation, only valence electrons of an atom take part.
Elements | Protons | Electrons | Neutrons | Atomic Number | Mass Number |
A | – | – | 10 | 8 | – |
B | 15 | – | – | – | 31 |
C | 1 | – | – | – | 3 |
D | – | 11 | 12 | – | – |
X | Y | |
Protons | 8 | 8 |
Neutrons | 8 | 10 |