p-Block Elements is Unit 10 of both the NEET UG and JEE Main syllabi, covering Groups 13 to 18. Both ask only for electronic configuration, general trends in physical and chemical properties and the unique behaviour of the first element of each group. The current NCERT books dropped this chapter, so these notes follow the syllabus and older NCERT editions.
p-Block Elements Notes for NEET and JEE Main
Group-wise trends, the inert pair effect, anomalous first elements, comparison tables and common mistakes for NEET and JEE Main 2027 revision.
p-Block Elements at a Glance
| Item | Details |
|---|---|
| Exams that cover it | NEET UG and JEE Main (Paper 1, B.E./B.Tech.) |
| Syllabus unit | Unit 10: p-Block Elements, Group 13 to Group 18 (same unit number in the NEET UG 2026 and JEE Main 2026 syllabi) |
| NCERT textbook | Not in the current rationalised NCERT Chemistry books. Older NCERT editions covered it in Class 11 Unit 11 (Groups 13 and 14) and Class 12 Unit 7 (Groups 15 to 18) |
| Linked chapter | Classification of Elements and Periodicity in Properties (Class 11 Unit 3), which explains the periodic trends used here |
| Syllabus topics | Group 13 to Group 18 elements: general introduction, electronic configuration and general trends in physical and chemical properties across the periods and down the groups; unique behaviour of the first element in each group |
| Official chapter | No current NCERT chapter PDF; the official NEET UG and JEE Main syllabus text is the reference |
| Notes PDF | Groups 13 and 14: View PDF; Groups 15 to 18: View PDF |
The topic list follows the NEET UG 2026 syllabus released by the National Medical Commission (NMC) on 22 December 2025 and NTA’s JEE Main 2026 syllabus, which stay the reference until the 2027 syllabi are out. The full NEET list is on the NEET syllabus page.
Both syllabi list only the general introduction and trends for this unit. Preparation, properties and structures of individual compounds, which the older NCERT chapters covered at length, are not listed, so this page keeps them to examples that explain a trend.
Which elements are in the p-block?
The p-block holds Groups 13 to 18, where the last electron enters a p orbital; the valence shell configuration runs from ns2 np1 to ns2 np6 (helium is the exception, 1s2).
| Group | Elements | Valence configuration | Common oxidation states | Trend in stability |
|---|---|---|---|---|
| 13 | B, Al, Ga, In, Tl | ns2 np1 | +3, +1 | +1 becomes more stable down the group; for Tl, +1 is more stable than +3 |
| 14 | C, Si, Ge, Sn, Pb | ns2 np2 | +4, +2 | +2 becomes more stable down the group; for Pb, +2 is more stable than +4 |
| 15 | N, P, As, Sb, Bi | ns2 np3 | –3, +3, +5 | +5 becomes less stable and +3 more stable down the group; for Bi, +3 is more stable |
| 16 | O, S, Se, Te, Po | ns2 np4 | –2, +2, +4, +6 | Oxygen mainly shows –2; +4 becomes more stable than +6 down the group |
| 17 | F, Cl, Br, I, At | ns2 np5 | –1; also +1, +3, +5, +7 except F | Fluorine shows only –1 |
| 18 | He, Ne, Ar, Kr, Xe, Rn | ns2 np6 (He: 1s2) | 0; Xe shows +2, +4, +6 in its fluorides and oxides | Only the heavier noble gases form compounds |
- Non-metallic character is highest at the top right of the block. Metallic character increases down each group.
- Boron is a non-metal; carbon, nitrogen, oxygen and the halogens are non-metals; bismuth, tin and lead are metals.
- The heavier elements of Groups 13 to 15 increasingly show an oxidation state two less than the group oxidation state.
What is the inert pair effect?
The inert pair effect is the reluctance of the ns2 electrons to take part in bonding as we go down Groups 13 to 15, which makes the lower oxidation state more stable.
- It arises because the intervening d and f electrons shield the nuclear charge poorly, so the heavier atoms hold their ns2 electrons more tightly.
- Group 13: Tl+ is more stable than Tl3+, so Tl(III) compounds are oxidising.
- Group 14: Pb2+ is more stable than Pb4+, so Pb(IV) compounds such as PbO2 are oxidising; Sn2+ compounds are reducing because tin prefers +4.
- Group 15: Bi(V) is unstable and bismuth prefers +3.
Trends in Physical Properties Down the Groups
Down each group atomic size increases, while ionisation enthalpy and electronegativity generally decrease; the d and f electrons in the heavier elements cause several irregularities.
| Property | General trend down a group | Exceptions to remember |
|---|---|---|
| Atomic radius | Increases as new shells are added | Ga is slightly smaller than Al, because the 3d electrons shield poorly |
| Ionisation enthalpy | Decreases | Group 13 values do not fall smoothly; Ga and Tl are higher than expected (poor shielding by d and f electrons) |
| Electronegativity | Decreases | In Group 13 it falls from B to Al and then rises slightly |
| Electron gain enthalpy | Becomes less negative | O is less negative than S and F less negative than Cl: the small first atom repels the incoming electron |
- Noble gases have very high ionisation enthalpies and large positive electron gain enthalpies, which explains their low reactivity.
- Boiling points of the noble gases increase down the group as van der Waals forces get stronger.
- Halogens are coloured because they absorb visible light: F2 yellow, Cl2 greenish yellow, Br2 red, I2 violet.
- Bond dissociation enthalpy of the halogens: Cl2 > Br2 > F2 > I2. F2 is low because of lone pair repulsion in the small molecule.
Why is the first element of each group different?
The first element of each group behaves differently because of its small size, high electronegativity, high ionisation enthalpy and the absence of d orbitals in its valence shell.
| Element | Unique behaviour | Example |
|---|---|---|
| Boron | Maximum covalency 4 (no d orbitals); non-metal; forms covalent compounds; its oxide is acidic | Al and the heavier elements can show covalency beyond 4 |
| Carbon | Maximum covalency 4; forms pπ–pπ multiple bonds with itself and with N and O; very strong catenation | C=C, C≡C, C=O; Si forms no such stable multiple bonds |
| Nitrogen | Forms pπ–pπ triple bond, so it exists as N2 gas; maximum covalency 4; hydrogen bonding in NH3 | N2 is diatomic, phosphorus is P4; R3P=O exists but R3N=O does not |
| Nitrogen (catenation) | N–N single bond is weaker than P–P because of lone pair repulsion | Catenation is weaker in nitrogen than in phosphorus |
| Oxygen | Small and highly electronegative: hydrogen bonding; pπ–pπ double bond, so O2 is a gas; mainly –2 state | H2O is a liquid while H2S is a gas; sulphur exists as solid S8 |
| Fluorine | Most electronegative element; only –1 state; no d orbitals; forms only one oxoacid (HOF) | HF is hydrogen bonded and is the weakest of the hydrogen halide acids |
Trends in Chemical Properties: Hydrides, Oxides and Halides
Down a group the hydrides become less stable and more reducing, the oxides become less acidic and more basic, and the heavier elements can expand their octet using d orbitals.
Hydrides
| Group | Hydrides | Trend down the group |
|---|---|---|
| 15 | NH3, PH3, AsH3, SbH3, BiH3 | Thermal stability and basic character decrease; reducing character increases (BiH3 is the strongest reducing agent); H–M–H bond angle decreases (NH3 about 107°) |
| 16 | H2O, H2S, H2Se, H2Te | Thermal stability decreases; acidic character increases; reducing character increases |
| 17 | HF, HCl, HBr, HI | Thermal stability decreases; acid strength increases: HF < HCl < HBr < HI |
Oxides
| Group | Acidic | Amphoteric | Basic or neutral |
|---|---|---|---|
| 13 | B2O3 | Al2O3, Ga2O3 | In2O3, Tl2O3 (basic) |
| 14 | CO2, SiO2, GeO2 | SnO, SnO2, PbO, PbO2 | CO is neutral |
| 15 | Oxides of N and P | Oxides of As and Sb | Bi2O3 (basic) |
- In Group 15 the oxide with the element in the higher oxidation state is more acidic, and acidic character decreases down the group.
- Group 16: reducing property of the dioxides decreases from SO2 to TeO2.
- Fluorine is more electronegative than oxygen, so its compounds with oxygen (OF2, O2F2) are oxygen fluorides.
Halides
- Group 13 trihalides are electron deficient and act as Lewis acids.
- Group 14 tetrahalides other than CCl4 are hydrolysed by water, because the heavier elements have vacant d orbitals to accept lone pairs from water.
- Group 15 forms EX3 and EX5. Nitrogen forms no pentahalide (no d orbitals). Pentahalides are more covalent than trihalides because the +5 state polarises the halide more.
- Group 16: the heavier elements can show +4 and +6 in halides (for example SF6), while oxygen cannot expand its octet.
Noble Gases: Group 18 Trends and Compounds
Noble gases are monatomic and very unreactive because of their stable ns2 np6 configuration, high ionisation enthalpy and large positive electron gain enthalpy.
- Neil Bartlett (1962) first made O2+[PtF6]–. Noting that the first ionisation enthalpy of xenon is almost the same as that of oxygen, he then prepared the red compound Xe+[PtF6]–.
- Xenon forms fluorides directly with fluorine: XeF2 is linear, XeF4 square planar and XeF6 distorted octahedral.
- Helium is used in diving air mixtures because it is much less soluble in blood than nitrogen.
- Radon is radioactive with a half-life of only 3.82 days, so its chemistry is hard to study.
Most-asked Facts for NEET and JEE Main: p-Block Elements
Revise these one-line facts just before the exam.
- Valence configuration of the p-block: ns2 np1 (Group 13) to ns2 np6 (Group 18); He is 1s2.
- Inert pair effect: the lower oxidation state becomes more stable down Groups 13 to 15 (Tl+, Pb2+, Bi3+).
- Ga is slightly smaller than Al because of poor shielding by the 3d electrons.
- B, C, N, O and F have a maximum covalency of 4 or less because they have no d orbitals.
- N2 has a very strong triple bond, so nitrogen is unreactive at room temperature.
- Nitrogen shows weaker catenation than phosphorus because the N–N single bond is weak.
- NH3 is the most basic and BiH3 the most reducing Group 15 hydride.
- Acid strength: HF < HCl < HBr < HI; acidity of Group 16 hydrides increases from H2O to H2Te.
- Most negative electron gain enthalpy in Group 17: chlorine, not fluorine.
- Bond dissociation enthalpy: Cl2 > Br2 > F2 > I2.
- Fluorine is the strongest oxidising halogen and shows only the –1 state.
- B2O3 is acidic, Al2O3 amphoteric, Tl2O3 basic; CO is neutral; Bi2O3 is basic.
- Nitrogen does not form NCl5; phosphorus forms PCl5.
- Halogen colours: F2 yellow, Cl2 greenish yellow, Br2 red, I2 violet.
- First noble gas compound work: Bartlett, Xe+[PtF6]–; XeF2 linear, XeF4 square planar.
Common Mistakes to Avoid
Watch for these mix-ups when you answer questions on this unit.
- Saying fluorine has the most negative electron gain enthalpy. Chlorine has; fluorine’s small size causes electron repulsion.
- Ranking F2 as the halogen with the strongest bond. Cl2 has the highest bond dissociation enthalpy; F2 is low because of lone pair repulsion.
- Calling HF the strongest hydrogen halide acid. It is the weakest; HI is the strongest.
- Treating +3 as the stable state of thallium or +4 as the stable state of lead. Inert pair effect makes Tl+ and Pb2+ more stable.
- Writing Al smaller than Ga. Ga is slightly smaller.
- Expecting nitrogen or oxygen to expand their octet (NCl5, OF6). They have no d orbitals in the valence shell.
- Calling CO an acidic oxide. CO is neutral, while CO2 is acidic.
- Assuming the basic character of Group 15 hydrides increases down the group. It decreases from NH3 to BiH3.
- Spending most revision time on the preparation of individual compounds from older books. The current syllabi list only general trends and the behaviour of the first element of each group.
p-Block Elements Notes PDF and Related Pages
Download the AglaSem notes (key notes and important questions with answers) free: Groups 13 and 14 (Class 11 notes) View PDF; Groups 15 to 18 (Class 12 notes) View PDF
- All chapters: NEET and JEE Main Chemistry notes
- Full topic list: NEET syllabus
- JEE Main topic list: JEE Main syllabus
- Practice: NEET question papers
- More practice: JEE Main question papers
- Source text: there is no current NCERT chapter; the unit is defined by the official NEET UG 2026 and JEE Main 2026 syllabus text
Chemistry Notes for NEET and JEE Main: All Chapters
- Some Basic Concepts of Chemistry
- Structure of Atom
- Chemical Kinetics
- Equilibrium
- Organic Chemistry: Some Basic Principles and Techniques
- Electrochemistry
- Amines
- Solutions
- Thermodynamics
- Coordination Compounds
- Haloalkanes and Haloarenes
- p-Block Elements
- Alcohols, Phenols and Ethers
- Hydrocarbons
- Aldehydes, Ketones and Carboxylic Acids
All chapters with key points and notes PDFs are on the Chemistry notes for NEET and JEE Main page.
p-Block Elements Notes for NEET and JEE Main FAQs
Is p-Block Elements in the NEET 2027 and JEE Main 2027 syllabus?
Yes. It is Unit 10, Group 13 to Group 18, in the latest syllabi of both exams: the NEET UG 2026 syllabus released by NMC on 22 December 2025 and NTA’s JEE Main 2026 syllabus. Only the general introduction, trends and the unique behaviour of the first element of each group are listed.
Which NCERT chapter covers p-Block Elements?
None of the current rationalised NCERT Chemistry books has this chapter. Older editions covered Groups 13 and 14 in Class 11 Unit 11 and Groups 15 to 18 in Class 12 Unit 7; use those editions and the syllabus text as the reference.
What is the inert pair effect?
It is the reluctance of the ns2 electrons to take part in bonding in the heavier elements of Groups 13 to 15, caused by poor shielding by d and f electrons. As a result Tl+, Pb2+ and Bi3+ are more stable than Tl3+, Pb4+ and Bi5+.
Why does nitrogen exist as N2 while phosphorus exists as P4?
Nitrogen is small enough to form strong pπ–pπ multiple bonds with itself, so it forms a stable N≡N molecule. Heavier phosphorus forms such bonds poorly, so it uses single bonds and exists as P4.
Are these notes enough for p-Block Elements questions?
They cover the trends the 2026 syllabi list. Read the syllabus text, revise periodic trends from the Classification of Elements chapter, use the notes PDFs for detail, and practise previous year questions to see how trend-based questions are asked.