# What is the electron configuration for Al^(+3) and As^-3?

$A {l}^{3 +} , Z = 13 :$ $1 {s}^{2} 2 {s}^{2} 2 {p}^{6}$ (the $3 s$ and $3 p$ electrons have been removed.
$A {s}^{3 -} , Z = 33 :$ $1 {s}^{2} 2 {s}^{2} 2 {p}^{6} 3 {s}^{2} 3 {p}^{6} 3 {d}^{10} 4 {s}^{2} 4 {p}^{6}$ (the $A {s}^{3 -}$ ion thus has the same electronic configuration as $K r$.