Question

according to the aufbau principle, which orbital is filled after 4s? 4d 4f 4p

Explanation:

The Aufbau principle states that electrons fill orbitals starting from the lowest - energy orbital. The order of filling is determined by the \(n + l\) rule (where \(n\) is the principal quantum number and \(l\) is the azimuthal quantum number). For the \(4s\) orbital (\(n = 4\), \(l=0\), \(n + l=4\)), after filling \(4s\), the next orbital to be filled is \(3d\) (\(n = 3\), \(l = 2\), \(n + l=5\)). But among the given options (\(4d\): \(n = 4\), \(l = 2\), \(n + l=6\); \(4f\): \(n = 4\), \(l = 3\), \(n + l = 7\); \(4p\): \(n = 4\), \(l=1\), \(n + l=5\)), if we consider the order after \(4s\) (ignoring the fact that \(3d\) comes before \(4p\) in the actual full - order but just among the given options), we use the \(n + l\) rule. The \(4p\) orbital has a lower \(n + l\) value (\(n + l = 5\)) compared to \(4d\) (\(n + l=6\)) and \(4f\) (\(n + l = 7\)).

Answer:

\(4p\)