Chemistry · Structure Of Atom · NEET
It tells you the SHAPE of the orbital and which subshell the electron is in. NCERT calls l the 'orbital angular momentum' or 'subsidiary' quantum number. So when NEET asks 'which quantum number gives the shape of the orbital?', the answer is l (azimuthal). Do not confuse it with n, which gives the SIZE.
l = 0 is the s subshell, l = 1 is p, l = 2 is d, and l = 3 is f. This never changes. So an orbital with n = 2, l = 1 is a 2p orbital. Learn it as: 0 to s, 1 to p, 2 to d, 3 to f.
This is a rule that comes out of the Schrodinger equation, so you must accept it. For a shell n, l can take exactly n different whole-number values, starting at 0 and stopping at (n-1). Example: for n = 3, l = 0, 1, 2, which are the 3s, 3p and 3d subshells. l can never equal n or be larger than n.
The number of subshells in a shell equals n. For n = 1 there is 1 subshell (1s). For n = 2 there are 2 subshells (2s, 2p). For n = 3 there are 3 subshells (3s, 3p, 3d). For n = 4 there are 4 subshells (4s, 4p, 4d, 4f). Just count l = 0 up to (n-1).
n (principal) gives the SIZE and main energy of the orbital. l (azimuthal) gives the SHAPE and names the subshell. Match-the-column NEET questions test this every year: n to size, l to shape, m(l) to orientation, m(s) to spin direction.
No. For n = 1, l can only be 0, so only 1s exists (no 1p). For n = 2, l can be 0 or 1, so only 2s and 2p exist (no 2d). A subshell exists only when its l value is allowed, meaning l is between 0 and (n-1). This is a very common NEET trap in 'incorrect set of quantum numbers' questions.
Match List-I (Quantum Number) with List-II (Information provided): (A) m_l (B) m_s (C) l (D) n --- (I) shape of orbital (II) size of orbital (III) orientation of orbital (IV) orientation of spin of electrons. Choose the correct option.
The incorrect set of quantum numbers from the following is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
They are directly linked. Each value of l names one subshell: l = 0 is s, 1 is p, 2 is d, 3 is f. So knowing l tells you the subshell straight away.
For n = 4, the maximum l is (n-1) = 3. So the fourth shell has l = 0, 1, 2, 3, which are the 4s, 4p, 4d and 4f subshells.
In a hydrogen atom, energy depends only on n. But in multi-electron atoms, energy depends on both n and l, and within one shell the order is s less than p less than d less than f (NCERT).
3d means n = 3 and l = 2 (because d corresponds to l = 2). This is valid because l = 2 is less than n = 3.
