A shell is made up of subshells. Subshells are regions of space where electron “clouds” are allowed to exist, and different subshells actually have different shapes. The first subshell is shaped like a sphere as illustrated in Fig 1.0(s) i.e. you can visualize it as a cloud of electrons surrounding the atomic nucleus in three dimensions. The second subshell consists of two “lobes” joined together at a single point near the atom’s center as shown in Fig 1.0(p). The third subshell typically resembles a set of four “lobes” clustered around the atom’s nucleus (Fig 1.0(d)).
Related: Principal Quantum Number
Valid angular momentum quantum numbers are positive integers like principal quantum numbers, but also include zero. These quantum numbers for electrons are symbolized by the letter l. The number of subshells in a shell is equal to the shell’s principal quantum number. Thus the first shell (n=1) has one subshell, numbered 0; the second shell (n=2) has two subshells, numbered 0 and 1; the third shell (n=3) has three subshells, numbered 0, 1, 2.
The previous convention for subshell description used letters rather numbers. In this notation, the first subshell (l=0) was designated s, the second subshell (l=1) was designated p, the third subshell (l=2) was designated d, and the fourth subshell (l=3) designated f. The letters come from the words sharp, principal, diffuse and fundamental.
Recommended Resource: Quantum Physics For Beginners
