# For Z=57, what is the element, and what is its electronic configuration?

I actually happen to know this one, because I did a lot of work with lanthanides, and actinides. Anyway, $Z = 57$ SPECIFIES the element $\text{lanthanum}$. And thus the electronic configuration has an xenon core ($X e , Z = 54$), i.e. $\left[X e\right] 5 {d}^{1} 6 {s}^{2}$. Lanthanum usually adopts the $+ I I I$ oxidation state, i.e. ${\left\{\left[X e\right]\right\}}^{3 +}$.....