How can we classify the group of elements by just looking at its valence configuration?

Electron configurations

Valence electrons are electrons used in forming bonds and are in the outer shell of an element.  

The bond that occurs can be either an ionic bond or a covalent bond  

Valence electron determination using electron configurations.  

The main group elements usually have valence electron configurations in the s and p subshells  

While the transition elements in the subshells (n-1) d  

Further explanation

The location of the elemental groups in the periodic system is determined by the number of valence electrons filling the last sub-shell  

The period of an element is determined from the valence shell (the biggest main quantum number (n) )

In an atom, there are levels of energy in the shell and subshell  

This energy level is expressed in the form of electron configurations.  

Writing electron configurations starts from the lowest to the highest sub-shell energy level. There are 4 sub-shells in the shell of an atom, namely s, p, d, and f. The maximum number of electrons for each subshell is  

s: 2 electrons  

p: 6 electrons  

d: 10 electrons and  

f: 14 electrons  

Charging electrons in the subshell uses the following sequence:  

1s², 2s², 2p⁶, 3s², 3p⁶, 4s², 3d¹⁰, 4p⁶, 5s², 4d¹⁰, 5p⁶, 6s², etc.  

the answer for sodium is 0.186

the answer for rubidium is 0.251