Atoms & structure
Orbital & subshell — অরবিটাল ও উপশেল
Quick answer
Shells split into subshells (s, p, d, f), and each subshell holds orbitals — regions where electrons are likely to be found.
Definition
Each shell is divided into subshells labelled s, p, d and f, which can hold 2, 6, 10 and 14 electrons respectively. A subshell is made of orbitals, each holding at most two electrons: the s subshell has one spherical orbital, p has three dumbbell-shaped ones, d five, f seven. An orbital is best pictured as a blurry cloud where the electron is most likely to be — not a fixed racetrack. Subshells explain why the periodic table has s, p, d and f blocks.
For example
Carbon's six electrons fill up as 1s² 2s² 2p²: the s subshell of K is full, L's s is full, and two electrons occupy L's p subshell.