Which quantum number is symbolized by l and indicates the shape of an orbital?

• A. Magnetic quantum number
• B. Spin quantum number
• C. Angular momentum number
• D. Principal quantum number

Answer: (C)

The key idea is the angular momentum quantum number, l. This quantity comes from the angular part of the electron’s wavefunction and determines the shape of the orbital. Each l value corresponds to a subshell type: l = 0 gives s orbitals (spherical), l = 1 gives p orbitals (figure with two lobes), l = 2 gives d orbitals (more complex four- or five-lobed shapes), and so on. The shapes arise from how the electron’s probability density distributes in space, which is described by the angular part of the wavefunction and the associated spherical harmonics.

Other quantum numbers play different roles: the principal quantum number n sets the overall size and energy, the magnetic quantum number m_l relates to orientation in space, and the spin quantum number m_s describes the electron’s intrinsic spin. So the symbol that indicates the shape of an orbital is the angular momentum quantum number, l.