Question

the calcium atom is bigger than the sodium atom ? explain

Answer 1

because it has a greater number of electrons, which are also found farther from the nucleus because of the orbital in which calcium’s valence electrons are found. The outtermost electrons of calcium are found at the 4s orbital, whereas the outtermost electron of sodium is found at 3s.

Now why is the 4s orbital more distant from the nucleus than the 3s orbital? That happens because, although Calcium has a greater number if protons, it has a lower effective nuclear charge than sodium, resulting in a weaker pull of its outtermost electrons, and thus a greater atomic radius.

Answer 2

Sodium's​ atomic no. is 11
electronic configuration - 2 , 8 , 1
It has three shells
Calcium's​ atomic no. is 20
electronic configuration - 2 , 8 , 8 , 2
It has 4 shells
As it has 1 more shell than Sodium so its size is more than Sodium.