the s subshell of the outermost energy shell, the d subshell of the next-to-outermost energy shell,
and the f subshell of the energy shell two levels below the outermost shell.
The last six columns of the periodic table contain elements with s and p valence electrons.
BASIC CONCEPT
left → right: atomic radius↓
ionization energy↑
electronegativity↑
(except for noble gases)
top → bottom: atomic radius↑
ionization energy↓
electronegativity↓