Quick answer: A periodic table NEET PYQ analysis of the chapter “Classification of Elements and Periodicity in Properties” shows that NTA usually asks one to two questions a year, and almost all of them test periodic trends: ionisation enthalpy (with its exceptions), electron gain enthalpy, the size of isoelectronic species, the nature of oxides, and the IUPAC names of elements with atomic number above 100.
This guide lists what NTA repeats, the exceptions you must know, and PYQ-pattern questions with answers. For the full Inorganic plan, see our NEET 2027 Inorganic Chemistry guide.
Want to test yourself first? Solve the Periodic Table PYQs for free, then use this guide to fix the gaps.
Table of Contents
Why the Periodic Table Chapter Matters
This chapter is small, but its trends run through the whole of Inorganic Chemistry. If you understand why atoms lose electrons more easily down a group, the s-block, p-block and d-block chapters become far easier. It also builds on electronic configuration from our Structure of Atom PYQ analysis, and it feeds directly into our Chemical Bonding PYQ analysis.
For chapter notes, use our Periodic Table class 11 notes. To see where it sits among other chapters, check the NEET 2027 chapter weightage.
Periodic Table NEET PYQ Analysis: What NTA Repeats
When you sort the past NEET chemistry PYQs from this chapter, six question types cover nearly everything.
| Question type | Frequency | What it tests |
|---|---|---|
| IE order | Most frequent | Trends and the Be > B, N > O exceptions |
| Electron affinity (ΔegH) | Very frequent | Cl > F, positive values for noble gases |
| Isoelectronic ions | Very frequent | Size order from nuclear charge |
| Atomic and ionic radius | Regular | Trends, Ga < Al |
| Nature of oxides and metallic character | Regular | Basic, amphoteric and acidic oxides |
| IUPAC names for Z > 100 | Regular | Nil, un, bi, tri… naming |
For the exceptions NTA loves across Inorganic Chemistry, see our list of Inorganic Chemistry exceptions and trends. For a quick warm-up, try these five quick periodic table questions.
The Periodic Trends Table
| Property | Across a period (left to right) | Down a group |
|---|---|---|
| Atomic radius | Decreases | Increases |
| Ionisation enthalpy (IE) | Increases (with exceptions) | Decreases |
| ΔegH | Becomes more negative (with exceptions) | Becomes less negative |
| Electronegativity | Increases | Decreases |
| Metallic character | Decreases | Increases |
| Non-metallic character | Increases | Decreases |
Fluorine has the highest electronegativity (4.0 on the Pauling scale). The modern periodic law, based on Moseley’s work, states that properties are a periodic function of atomic number, not atomic mass as in Mendeleev’s law.
Ionisation Enthalpy: The Exceptions That Get Asked
Ionisation enthalpy is the energy needed to remove the outermost electron from an isolated gaseous atom. In general it rises across a period, but two exceptions in Period 2 (and the same pattern in Period 3) are asked every few years:
| Exception | Reason |
|---|---|
| Be > B | Removing a 2p electron from B is easier than removing a 2s electron from Be, because 2s is more penetrating and is held more strongly |
| N > O | N has a stable half-filled 2p³ configuration; in O, two electrons share one 2p orbital and repel each other |
So the correct order of first IE in Period 2 is:
Li < B < Be < C < O < N < F < Ne
The same pattern gives Mg > Al and P > S in Period 3. Successive ionisation enthalpies always increase (IE₂ > IE₁), because the electron is removed from a positive ion.
Electron Gain Enthalpy
Electron gain enthalpy (ΔegH) is the enthalpy change when an isolated gaseous atom gains an electron.
- Chlorine has the most negative value (about −349 kJ/mol), more negative than fluorine (about −328 kJ/mol). The 2p subshell of fluorine is so small that the added electron feels strong repulsion from the electrons already there.
- The order for halogens is Cl > F > Br > I (in magnitude).
- In the same way, sulphur has a more negative value than oxygen.
- Noble gases have large positive values, because the added electron must enter a new, higher shell.
Isoelectronic Species
Isoelectronic species have the same number of electrons. Among them, a higher nuclear charge pulls the electrons in more, so the ion is smaller.
N³⁻ > O²⁻ > F⁻ > Na⁺ > Mg²⁺ > Al³⁺ (all have 10 electrons)
The rule to remember: for such ions, the more protons, the smaller the size. Two more facts: a cation is always smaller than its parent atom, and an anion is always larger.
Radius Facts That Trap Students
- Gallium is smaller than aluminium (about 135 pm vs 143 pm). The ten 3d electrons in Ga shield the nucleus poorly, so the outer electrons feel a higher effective nuclear charge.
- Noble gases are usually given a van der Waals radius, which is larger than the covalent radius of the halogen before them, so they are excluded when you compare atomic radii across a period.
Nature of Oxides
| Trend | Example |
|---|---|
| Across a period: basic → amphoteric → acidic | Na₂O (strongly basic), Al₂O₃ (amphoteric), Cl₂O₇ (strongly acidic) |
| Down a group: oxides become more basic | Metallic character increases down the group |
Amphoteric oxides such as Al₂O₃ react with both acids and bases, and NTA often hides one among basic and acidic options.
IUPAC Names for Elements With Z > 100
Each digit of the atomic number gets a root, and the name ends in “-ium”.
| Digit | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
|---|---|---|---|---|---|---|---|---|---|---|
| Root | nil | un | bi | tri | quad | pent | hex | sept | oct | enn |
Examples: Z = 101 is unnilunium (Unu), Z = 104 is unnilquadium (Unq), Z = 109 is unnilennium (Une) and Z = 120 is unbinilium (Ubn).
Blocks and Electronic Configuration
| Block | General outer configuration | Groups |
|---|---|---|
| s-block | ns¹⁻² | 1 and 2 |
| p-block | ns² np¹⁻⁶ | 13 to 18 |
| d-block | (n−1)d¹⁻¹⁰ ns⁰⁻² | 3 to 12 |
| f-block | (n−2)f¹⁻¹⁴ (n−1)d⁰⁻¹ ns² | Lanthanoids and actinoids |
To place an element: the period is the highest principal quantum number, and the block is the subshell that receives the last electron.
Worked PYQ-Pattern Questions
Q1. The correct order of first IE is: (a) B < C < N < O (b) B < C < O < N (c) C < B < O < N (d) B < O < C < N
Answer: (b) B < C < O < N. Nitrogen is higher than oxygen because of its stable half-filled 2p³ configuration.
Q2. Which element has the most negative ΔegH? (a) F (b) Cl (c) Br (d) O
Answer: (b) Cl. Fluorine’s small 2p subshell causes electron repulsion, so its value is less negative than chlorine’s.
Q3. Among N³⁻, O²⁻, F⁻ and Na⁺, the largest ion is:
Answer: N³⁻. All four have 10 electrons, and N³⁻ has the fewest protons (7), so its electrons are held least tightly.
Q4. The IUPAC name of the element with atomic number 114 is:
Answer: Ununquadium (Uuq). 1 = un, 1 = un, 4 = quad, plus “-ium”.
Q5. Which of these oxides is amphoteric? (a) Na₂O (b) CaO (c) Al₂O₃ (d) SO₃
Answer: (c) Al₂O₃. It reacts with both acids and bases; Na₂O and CaO are basic, and SO₃ is acidic.
Common Traps in This Chapter
- Writing F as the element with the most negative ΔegH (it is Cl)
- Writing the Period 2 IE order without the Be > B and N > O exceptions
- Saying Ga is larger than Al
- Ranking isoelectronic ions by charge size alone instead of by nuclear charge
- Forgetting that noble gases have a positive ΔegH
- Mixing up “quad” (4) and “pent” (5) in IUPAC names
Practise Every Periodic Table PYQ
This periodic table NEET PYQ analysis shows you where the marks are. Solving real past questions makes those trends and exceptions automatic. Every previous year question from this chapter is available chapter-wise, free:
👉 Solve all Periodic Table NEET PYQs
Keep the trends table beside you for the first round, then solve the second round without it.
Conclusion
The Periodic Table chapter is short, but its trends run through all of Inorganic Chemistry. Use this periodic table NEET PYQ analysis to master the IE exceptions, electron gain enthalpy, isoelectronic ions, oxide nature and IUPAC naming. Then practise the past questions until the orders come to you without thinking.
FAQ
Q: How many questions come from the Periodic Table chapter in NEET? A: Usually one to two questions a year, mostly on periodic trends and their exceptions.
Q: What is the most important topic in Classification of Elements for NEET? A: The IE order with its exceptions is the most tested, followed by electron affinity and the size of isoelectronic ions.
Q: Why does chlorine have a more negative electron gain enthalpy than fluorine? A: Fluorine’s 2p subshell is very small, so an added electron is strongly repelled by the electrons already present. Chlorine’s larger 3p subshell has less repulsion.
Q: Why is the IE of nitrogen higher than that of oxygen? A: Nitrogen has a stable half-filled 2p³ configuration. In oxygen, two electrons are paired in one 2p orbital, and their repulsion makes one easier to remove.
Q: How do I revise the Periodic Table chapter quickly? A: Use a periodic table NEET PYQ analysis to list the repeated trends and exceptions, learn the trends table and the exception list, and solve the past questions chapter-wise.
Q: Where can I practise Periodic Table NEET PYQs for free? A: You can solve every previous year question from Classification of Elements and Periodicity in Properties chapter-wise for free using the practice links in this article.