Which is the bigger atom: aluminum or sodium?

1 Answer
May 16, 2016

Consider atomic numbers, #Z#, of each element.


#Na, Z=11#; #Al, Z=13#.

Aluminum has greater nuclear charge. While aluminum has more electrons, valence electrons are known to shield each other very imperfectly. The increased effective nuclear charge tends to decrease atomic radii across the Period from left to right.

As a physical scientist, you should put some numbers up for discussion. Here is a start. The different ionization energies can be rationalized on a Periodic basis.