Structure of Atom for NEET UG
Where are an atom's electrons and how much energy do they have? Quantum numbers, orbitals and electronic configuration answer this, and they explain the whole periodic table.
ChemistryClass 1175 MCQs3 lessons14 flashcards4 memory tricks
Practise Structure of Atom free
What you'll learn
- Subatomic particles and Bohr's model
Count protons, neutrons and electrons, and use Bohr's energy formula for hydrogen. - Quantum numbers and orbitals
Assign the four quantum numbers and describe the shapes of s, p and d orbitals. - Electronic configuration
Write configurations using the Aufbau principle, Pauli's principle and Hund's rule, including exceptions.
Key formulas
| Atomic number | Z = number of protons |
|---|---|
| Mass number | A = protons + neutrons |
| Energy of nth orbit (hydrogen-like) | Eₙ = −13.6 Z²/n² eV |
| Radius of nth orbit | rₙ = 0.529 n²/Z Å |
Memory tricks
Sharp, Principal, Diffuse, Fundamental.
Within a subshell, electrons fill each orbital singly with parallel spins before any pairing begins.
No two electrons in an atom can have the same set of four quantum numbers, so an orbital holds at most two electrons, with opposite spins.
4s (4 + 0 = 4) fills before 3d (3 + 2 = 5). 3d and 4p both have 5, so 3d (n = 3) goes first.
Try 3 NEET-style questions
Q1. In multi-electron atoms, for the same principal quantum number, the energies of subshells increase in the order
- f < d < p < s
- p < s < d < f
- all are equal
- s < p < d < f
Show answer
Answer: (4) s < p < d < f
For the same n, s electrons penetrate closer to the nucleus and are more tightly bound. Energy increases s < p < d < f.
Q2. The d orbital whose lobes lie along the x and y axes is
- d(xy)
- d(x²−y²)
- d(yz)
- d(xz)
Show answer
Answer: (2) d(x²−y²)
The d(x²−y²) orbital has its lobes along the x and y axes. d(xy), d(yz) and d(xz) have lobes between the axes.
Q3. According to Hund's rule of maximum multiplicity,
- electrons pair up before any orbital is singly occupied
- each orbital of a subshell gets one electron before pairing starts
- pairing occurs only in the lowest orbital
- electrons avoid the same spin
Show answer
Answer: (2) each orbital of a subshell gets one electron before pairing starts
Electrons occupy all orbitals of a subshell singly, with parallel spins, before any pairing begins.
Practise all 75 questions Free · explanations for every option · see where you go wrong