Final answer:
The letter 's' denotes a spherical orbital in quantum chemistry, which is characterized by its symmetrical spherical shape.
Step-by-step explanation:
The letter used to denote a spherical orbital is 's'. In quantum chemistry, the s orbital is characterized by its spherical shape, in contrast to other orbital types like the p, d, and f orbitals which have different shapes and orientations. For example, a 1s orbital is smaller and has only one electron cloud surrounding the nucleus, while 2s and 3s orbitals are progressively larger with the same spherical distribution around the nucleus.
The letter s is used to denote a spherical orbital. An s orbital is spherically symmetric and has a spherical shape. It is represented by the quantum number n=1 and l=0. The s subshell has only one orbital, which is spherically symmetrical, like a ball with a nucleus at the center.