How much of JEE Main comes from Classification of Elements and Periodicity?

JEEGenie estimates about 3% of JEE Main marks come from Classification of Elements and Periodicity, based on recent papers. The share varies from year to year.

Which formulas matter most in Classification of Elements and Periodicity?

The Classification of Elements and Periodicity sheet on this page has 7 formula entries, starting with Effective Nuclear Charge (Zeff), Ionization Enthalpy (IE), Electron Gain Enthalpy (ΔegH), Electronegativity (χ), Electronic Configuration and Position. Each one comes with when to use it and the trap to avoid.

What topics does Classification of Elements and Periodicity cover for JEE?

Classification of Elements and Periodicity covers Periodic Classification, Atomic and Ionic Radii, Ionisation Enthalpy, Electronegativity, Electron Gain Enthalpy, Periodic Trends.

How should I revise Classification of Elements and Periodicity before the exam?

Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens Classification of Elements and Periodicity questions on JEEGenie.

How many previous-year questions are there on Classification of Elements and Periodicity?

JEEGenie has 333 previous-year questions on Classification of Elements and Periodicity, and this page shows a few with worked explanations.

Is practice on Classification of Elements and Periodicity free on JEEGenie?

Sign-up is free and includes a 7-day Pro trial. After the trial, free accounts keep a limited daily quota.

Classification of Elements and Periodicity for JEE Main & Advanced — formulas, what is asked, and traps

JEEGenie estimates about 3% of JEE Main marks come from Classification of Elements and Periodicity. This page covers 7 formula entries, each with when to use it, what JEE asks and the traps. A common slip: Students often confuse Mendeleev's law with modern law, forgetting that atomic number is the fundamental property.

Key points to know

Mendeleev's Periodic Law vs Modern Periodic Law. Mendeleev arranged elements by atomic mass; Modern law arranges by atomic number (Z). Modern law corrects anomalies like Ar-K and Co-Ni ordering.
Periodicity. Periodicity is the repetition of properties after regular intervals of increasing atomic number due to similar valence shell electronic configurations.
Atomic Radius Trends. Atomic radius decreases across a period (Zeff increases) and increases down a group (addition of shells).
Ionization Enthalpy (IE). Energy required to remove an electron from a gaseous atom. IE increases across a period (Zeff increases) and decreases down a group (size increases).
Electronegativity (χ). Tendency of an atom to attract shared electrons in a bond. Increases across period, decreases down group. Pauling scale: χ(F)=4.0, χ(O)=3.5, χ(N)=3.0.
Metallic and Non-Metallic Character. Metals: low IE, low EN, good conductors. Non-metals: high IE, high EN, poor conductors. Metalloids: intermediate properties (B, Si, Ge, As, Sb, Te).
Periodic Table Blocks. s-block: groups 1-2 (ns¹⁻²). p-block: groups 13-18 (ns²np¹⁻⁶). d-block: groups 3-12 (ns²(n-1)d¹⁻¹⁰). f-block: inner transition (lanthanides and actinides).
Lanthanide Contraction. Gradual decrease in atomic and ionic radii of lanthanides (Ce to Lu) due to poor shielding of 4f electrons. Causes Zr-Hf, Nb-Ta, Mo-W to have similar properties.
Oxidation States and Periodicity. Maximum oxidation state = number of valence electrons (group number for groups 1-2; group - 10 for p-block) or sum of s and d electrons (for d-block). Transition metals show variable oxidation states. p-block elements show negative states = -(8 - valence electrons) = group - 18.
Diagonal Relationship. Similarity between Li-Mg, Be-Al, B-Si due to similar charge/radius ratio. They form covalent compounds, react with N₂, etc.
Periodicity in Chemical Properties. Oxides: basic (metals), amphoteric (metalloids), acidic (non-metals). Hydrides: ionic (s-block), covalent (p-block), metallic (d-block). Halides: ionic (s-block), covalent (p-block).
Periodicity of Valence Electrons. Valence electrons = group number for groups 1-2; = group number - 10 for groups 13-18 (He has 2). d-block: (n-1)d + ns electrons. f-block: usually 3 valence electrons.
Electropositivity. Tendency to lose electrons; increases down group, decreases across period. Metals are electropositive, non-metals are electronegative.

Formula sheet

Name	Formula	When to use
Effective Nuclear Charge (Zeff)	$Z_{eff} = Z - σ$	When comparing atomic radii, ionization energy, or electron gain enthalpy of elements.
Ionization Enthalpy (IE)	$M (g) \to M^{+} (g) + e^{-} Δ H = {IE}_{1}$	When comparing ease of electron removal or metallic character.
Electron Gain Enthalpy (ΔegH)	$X (g) + e^{-} \to X^{-} (g) Δ H = Δ_{eg} H$	When comparing tendency to form anions or oxidizing power.
Electronegativity (χ)	$χ_{A} - χ_{B} = 0.102 \sqrt{Δ}$ (Pauling), where Δ = bond energy difference	When predicting bond polarity, dipole moment, or acid-base strength.
Electronic Configuration and Position	s-block: group = ns electrons; p-block: group = 10 + (ns + np electrons); for d-block: group = (n-1)d + ns electrons (except anomalies).	When determining period and group from electronic configuration.
Pauling's Electronegativity Scale	$χ_{A} - χ_{B} = 0.102 \sqrt{Δ}$	When calculating electronegativity difference from bond energies.
Mulliken's Electronegativity	$χ_{Mulliken} = \frac{I E + E A}{2}$	When given IE and EA values to compute electronegativity.

Open the Classification of Elements and Periodicity formula page

What JEE asks

Mendeleev's Periodic Law vs Modern Periodic Law. JEE asks direct questions on the basis of periodic law (atomic number vs mass) and anomalies.
Periodicity. JEE tests the reason behind periodicity (electronic configuration) and asks to identify periodic properties.
Effective Nuclear Charge (Zeff). JEE asks to calculate Zeff using Slater's rules for a given electron or compare Zeff across period/group.
Slater's Rules for Shielding Constant (σ). JEE often asks to compute Zeff for a valence electron in elements like Na, Cl, or transition metals.
Atomic Radius Trends. JEE asks to arrange elements in order of atomic radius or identify the largest/smallest in a period.
Ionization Enthalpy (IE). JEE asks to predict IE order, identify exceptions, or calculate IE from Born-Haber cycle.
Electron Gain Enthalpy (ΔegH). JEE asks to order elements by ΔegH or identify the most negative (e.g., Cl > F).
Electronegativity (χ). JEE asks to compare electronegativity of elements or use it to determine bond type.
Periodic Trends Comparison. JEE often asks to arrange elements in order of a property or identify the odd one out.
Metallic and Non-Metallic Character. JEE asks to identify metalloids or predict reactivity based on metallic character.
Periodic Table Blocks. JEE asks to identify block from electronic configuration or vice versa.
Electronic Configuration and Position. JEE asks to find group number of an element given its configuration.
Identifying Anomalies in Periodic Trends. JEE directly asks to identify the element with higher IE or more negative ΔegH among pairs.
Lanthanide Contraction. JEE asks cause and consequences of lanthanide contraction.
Oxidation States and Periodicity. JEE asks to predict common oxidation states or identify elements showing inert pair effect.
Inert Pair Effect. JEE asks to explain stability of lower oxidation states in heavier p-block elements.
Diagonal Relationship. JEE asks to identify pairs with diagonal relationship or explain similarities.
Periodicity in Chemical Properties. JEE asks to predict nature of oxides or hydrides based on element's position.
Pauling's Electronegativity Scale. JEE may ask to compute χ difference given bond energies or vice versa.
Mulliken's Electronegativity. JEE may ask to compare Mulliken and Pauling scales or compute χ.
Periodicity of Valence Electrons. JEE asks to determine number of valence electrons from configuration.
Electropositivity. JEE asks to arrange elements by electropositivity or identify the most electropositive.
Predicting Properties from Position. JEE often asks to identify an element from its position and then predict its chemical behavior.

Common traps

Students often confuse Mendeleev's law with modern law, forgetting that atomic number is the fundamental property. Mendeleev's Periodic Law vs Modern Periodic Law
Do not confuse periodicity with periodic table groups; periodicity refers to trends across periods. Periodicity
Do not forget that σ depends on electron's group and orbital (Slater's rules). Effective Nuclear Charge (Zeff)
Do not mix rules for ns/np and nd/nf; nd/nf have no 0.85 factor. Slater's Rules for Shielding Constant (σ)
Do not confuse atomic radius with ionic radius; cations are smaller, anions larger. Atomic Radius Trends
IE2 > IE1 always; do not compare IE1 of different elements without considering electronic configuration. Ionization Enthalpy (IE)
Do not confuse with electronegativity; ΔegH is an experimental enthalpy, electronegativity is a relative scale. Electron Gain Enthalpy (ΔegH)
Electronegativity is not a physical property; it is a relative scale. Electronegativity (χ)
Do not apply trends blindly; exceptions like F vs Cl for ΔegH (Cl more negative). Periodic Trends Comparison
Do not assume all elements in a group are metals; e.g., C is non-metal, Si is metalloid. Metallic and Non-Metallic Character
Do not confuse d-block with transition metals; d-block includes Zn, Cd, Hg which are not transition metals (full d10). Periodic Table Blocks
For d-block, group = sum of (n-1)d and ns electrons (e.g., Fe: 3d⁶4s² → group 8). Electronic Configuration and Position
Do not assume all trends are monotonic; these exceptions are frequently tested. Identifying Anomalies in Periodic Trends
Do not think lanthanide contraction only affects lanthanides; it affects post-lanthanide elements (e.g., Hf similar to Zr). Lanthanide Contraction

Topics in Classification of Elements and Periodicity

Periodic Classification
Atomic and Ionic Radii
Ionisation Enthalpy
Electronegativity
Electron Gain Enthalpy
Periodic Trends

Previous-year questions on Classification of Elements and Periodicity

JEEGenie has 333 previous-year questions on Classification of Elements and Periodicity. A few worked examples follow.

Year	Questions
2026	18
2025	28
2024	28
2023	15
2022	16
2021	20
2020	18
2019	18
2018	2
2017	5
2016	3
2015	5
2014	5
2013	11
2012	5
2011	2
2010	2
2009	3
2008	1
2007	2
2006	2
2005	2
2004	3
2003	3
2002	4
2001	2
2000	7
1999	4
1998	8
1997	8
1996	6
1995	1
1994	2
1993	5
1992	5
1991	6
1990	3
1989	6
1988	6
1987	10
1986	7
1985	6
1984	4
1983	4
1982	4
1981	3
1980	2
1979	2
1978	1

Question 1 easy

The correct set that contains all kinds (basic, acidic, amphoteric and neutral) of oxides is :

$N a_{2} O$ , $K_{2} O$ , $A l_{2} O_{3}$ and $A s_{2} O_{3}$
$A l_{2} O_{3}$ , $A s_{2} O_{3}$ , CO and NO
$K_{2} O$ , $C l_{2} O_{7}$ , $A s_{2} O_{3}$ and NO
$N a_{2} O$ , $N_{2} O$ , $A l_{2} O_{3}$ and CO

Answer: C

Explanation. 1. Classify each oxide in option (C): -

K_{2} O

: oxide of an alkali metal

\to

**basic oxide**. -

C l_{2} O_{7}

: oxide of a non-metal (chlorine)

\to

**acidic oxide**. -

A s_{2} O_{3}

: oxide of a metalloid

\to

**amphoteric oxide**. -

N O

: oxide of nitrogen in +2 state, does not react with acids or bases

\to

**neutral oxide**. 2. Thus, option (C) contains one basic, one acidic, one amphoteric, and one neutral oxide. 3. Check other options: - (A)

N a_{2} O, K_{2} O

(both basic),

A l_{2} O_{3}, A s_{2} O_{3}

(both amphoteric)

\to

no acidic or neutral oxide. - (B)

A l_{2} O_{3}, A s_{2} O_{3}

(both amphoteric),

C O, N O

(both neutral)

\to

no basic or acidic oxide. - (D)

N a_{2} O

(basic),

N_{2} O, C O

(both neutral),

A l_{2} O_{3}

(amphoteric)

\to

no acidic oxide. 4. Therefore, the correct set is

C

From NTA/IIT papers: JEE Main 2026 · 2 Apr Shift 2

Question 2 medium

Which of the following statements are correct? A. The process of adding an electron to a neutral gaseous atom is always exothermic. B. The process of removing an electron from an isolated gaseous atom is always endothermic. C. The

1^{st}

ionization energy of boron is less than that of beryllium. D. The electronegativity of C is 2.5 in

{C H}_{4}

and

{C C l}_{4}

E. Li is the most electropositive among elements of group I. Choose the correct answer from the options given below:

A, C and D Only
B and C Only
B and D Only
B, C and E Only

Answer: B

Explanation. A: Adding an electron can be exothermic or endothermic (e.g., noble gases). So A is false. B: Removing an electron requires energy input, always endothermic. B is true. C: Beryllium has stable

2 s^{2}

configuration; boron has

2 s^{2} 2 p^{1}

, so removing a

2 p

electron is easier. Thus first IE of B < Be. C is true. D: Electronegativity depends on the bonding atom; in

{C C l}_{4}

, C is less electronegative than Cl, but the value is not fixed at 2.5 in all compounds. D is false. E: Among group I, Cs is most electropositive, not Li. E is false. Correct statements: B and C only. Answer is option B.

From NTA/IIT papers: JEE Main 2025 · 3 Apr Shift 1

Question 3 medium

The correct order of first ionization enthalpy values of the following elements is : (A) O (B) N (C) Be (D) F (E) B Choose the correct answer from the options given below :

$A < B < D < C < E$
$C < E < A < B < D$
$E < C < A < B < D$
$B < D < C < E < A$

Answer: C

Explanation. We compare first ionization enthalpies across periods 2 and 3. - Across a period, generally increases left to right, but exceptions occur due to stable configurations. - Be (

1 s^{2} 2 s^{2}

) has higher IE than B (

1 s^{2} 2 s^{2} 2 p^{1}

) because B loses a

2 p

electron more easily. So

B < B e

. - N has half-filled

2 p^{3}

(extra stability), so IE of N > O. - F has the highest IE in period 2. Order from lowest to highest: B (E) < Be (C) < O (A) < N (B) < F (D). Thus,

E < C < A < B < D

. The correct answer is option C.

From NTA/IIT papers: JEE Main 2024 · 4 Apr Shift 1

Question 4 easy

Group-13 elements react with

O_{2}

in amorphous form to form oxides of type

M_{2} O_{3} (M =

element). Which among the following is the most basic oxide?

Al $_{2}$ O $_{3}$
TI $_{2}$ O $_{3}$
B $_{2}$ O $_{3}$
Ga $_{2}$ O $_{3}$

Answer: B

Explanation. Down group 13, basic character of

M_{2} O_{3}

increases as metallic character increases.

B_{2} O_{3}

is acidic,

{A l}_{2} O_{3}

is amphoteric,

{G a}_{2} O_{3}

and

{I n}_{2} O_{3}

are also amphoteric but less acidic. Thallium (

T l

) is the most metallic in group 13, so

{T l}_{2} O_{3}

is the most basic oxide. Thus, the answer is option B.

From NTA/IIT papers: JEE Main 2023 · 6 Apr Shift 2

Question 5 hard

The 1st, 2nd, and the 3rd ionization enthalpies,

I_{1}

I_{2}

, and

I_{3}

, of four atoms with atomic numbers

n

n + 1

n + 2

, and

n + 3

, where

n < 10

, are tabulated below. What is the value of

n

? Data (Atomic number :

I_{1}

;

I_{2}

;

I_{3}

in kJ/mol):

n

: 1681 ; 3374 ; 6050.

n + 1

: 2081 ; 3952 ; 6122.

n + 2

: 496 ; 4562 ; 6910.

n + 3

: 738 ; 1451 ; 7733.

Answer: 9

Explanation. For

n < 10

, the elements are in the second period (Li to Ne). A very low

I_{1}

(496 kJ/mol) for

n + 2

indicates an alkali metal, so

n + 2

must be Li (

Z = 3

). Thus

n = 1

, but

n

must be an atomic number

\geq 1

; check consistency: -

n = 1

(H):

I_{1} = 1312

kJ/mol, not 1681

\to

reject. - Try

n = 3

(Li):

I_{1} = 520

kJ/mol, not 1681

\to

reject. - Try

n = 4

(Be):

I_{1} = 899

kJ/mol, not 1681

\to

reject. - Try

n = 5

(B):

I_{1} = 801

kJ/mol, not 1681

\to

reject. - Try

n = 6

(C):

I_{1} = 1086

kJ/mol, not 1681

\to

reject. - Try

n = 7

(N):

I_{1} = 1402

kJ/mol, not 1681

\to

reject. - Try

n = 8

(O):

I_{1} = 1314

kJ/mol, not 1681

\to

reject. - Try

n = 9

(F):

I_{1} = 1681

kJ/mol

\to

matches! Check

n + 1 = 10

(Ne):

I_{1} = 2081

kJ/mol

\to

matches.

n + 2 = 11

(Na):

I_{1} = 496

kJ/mol

\to

matches.

n + 3 = 12

(Mg):

I_{1} = 738

kJ/mol

\to

matches. All

I_{2}, I_{3}

also match known values.

9

From NTA/IIT papers: JEE Advanced 2020

Frequently asked questions

How much of JEE Main comes from Classification of Elements and Periodicity?: JEEGenie estimates about 3% of JEE Main marks come from Classification of Elements and Periodicity, based on recent papers. The share varies from year to year.
Which formulas matter most in Classification of Elements and Periodicity?: The Classification of Elements and Periodicity sheet on this page has 7 formula entries, starting with Effective Nuclear Charge (Zeff), Ionization Enthalpy (IE), Electron Gain Enthalpy (ΔegH), Electronegativity (χ), Electronic Configuration and Position. Each one comes with when to use it and the trap to avoid.
What topics does Classification of Elements and Periodicity cover for JEE?: Classification of Elements and Periodicity covers Periodic Classification, Atomic and Ionic Radii, Ionisation Enthalpy, Electronegativity, Electron Gain Enthalpy, Periodic Trends.
How should I revise Classification of Elements and Periodicity before the exam?: Learn each formula together with its condition of use, read the trap listed beside it, then practise questions and review every mistake. The practice link on this page opens Classification of Elements and Periodicity questions on JEEGenie.
How many previous-year questions are there on Classification of Elements and Periodicity?: JEEGenie has 333 previous-year questions on Classification of Elements and Periodicity, and this page shows a few with worked explanations.
Is practice on Classification of Elements and Periodicity free on JEEGenie?: Sign-up is free and includes a 7-day Pro trial. After the trial, free accounts keep a limited daily quota.