Classification of Elements & Periodicity Formula Sheet — JEE Main Chemistry

Q: What are the most important Classification of Elements & Periodicity formulas for JEE Main?

This Classification of Elements & Periodicity formula sheet covers all the high-yield Chemistry formulas, definitions and theorems you need for JEE Main, across Modern periodic law, Present form of periodic table, s, p, d and f block elements, Periodic trends in properties, Atomic and ionic radii — each shown with the key result and, where useful, a worked example.

Q: Is this Classification of Elements & Periodicity formula sheet free?

Yes — the full chapter formula sheet is free to read online, no login or payment required.

Q: How should I revise Classification of Elements & Periodicity formulas?

Blurt the Classification of Elements & Periodicity formulas from memory, then check against this sheet to find your gaps — and practise a few previous-year questions on the chapter to make sure you can apply them under time pressure.

Every key Classification of Elements & Periodicity formula, definition and theorem for JEE Main Chemistry in one place — with common examiner traps and worked examples. Free to read; blurt from memory, then check your gaps.

Syllabus — topics coveredNTA · 9 sub-topics

Modern periodic law
Present form of periodic table
s, p, d and f block elements
Periodic trends in properties
Atomic and ionic radii
Ionization enthalpy
Electron gain enthalpy
Valence and oxidation states
Chemical reactivity

Modern Periodic Law & the Long-Form Table

From Mendeleev to the modern law

▸ $Mendeleev$ arranged elements by increasing $atomic mass$ and predicted undiscovered elements (eka-aluminium etc.).
▸ $Moseley$ showed properties depend on $atomic number$ Z, not mass — resolving anomalies (e.g. Ar before K).
▸Atomic number = number of protons = the true basis of classification.

Modern periodic law: The physical and chemical properties of the elements are a

periodic function of their atomic numbers

. Elements with similar valence-shell configurations recur at regular intervals.

★ Remember · Anatomy of the table

7 periods

(horizontal rows, set by the value of n of the valence shell) and

18 groups

(vertical columns / families with the same valence configuration).

Period	$n$	Elements	Sub-shells filled
1	1	2	$1 s$
2	2	8	$2 s 2 p$
3	3	8	$3 s 3 p$
4	4	18	$4 s 3 d 4 p$
5	5	18	$5 s 4 d 5 p$
6	6	32	$6 s 4 f 5 d 6 p$
7	7	32	$7 s 5 f 6 d 7 p$

Why those lengths?

▸Number of elements in a period $=$ $twice$ the number of orbitals filled in that energy level.
▸ $4 f$ fills in period 6 and $5 f$ in period 7, giving the 32-element rows.
▸Filling follows the $aufbau$ order ( $4 s$ before $3 d$ , etc.).

🚫 Examiner Trap · Examiner traps

(1) The modern law uses

atomic number

Z (Moseley), not atomic mass (Mendeleev) — this fixed anomalies like Ar-before-K. (2) Period

=

value of n of the valence shell; period lengths

2, 8, 8, 18, 18, 32, 32

. (3) Number of elements in a period

= 2 \times

orbitals filled. (4) Group number gives the valence-shell configuration.

Electronic Configuration & the s, p, d, f Blocks

Blocks of the periodic table: Elements are grouped into

four blocks

— s, p, d, f — according to the type of atomic orbital that receives the last (differentiating) electron.

Long-form periodic table coloured by block: s-block in groups 1-2, p-block in groups 13-18, d-block in groups 3-12, and the f-block lanthanoids and actinoids shown detached below, with the valence configuration of each block — The four blocks and their valence configurations; the $f$ -block sits detached below.

s

-block (Gr 1–2)

n s^{1 - 2}

p

-block (Gr 13–18)

n s^{2} n p^{1 - 6}

d

-block (Gr 3–12)

(n - 1) d^{1 - 10} n s^{0 - 2}

f

-block

(n - 2) f^{1 - 14} (n - 1) d^{0 - 1} n s^{2}

Locating an element from its configuration

▸ $Period$ $=$ highest principal quantum number n in the configuration.
▸ $Block$ $=$ sub-shell receiving the last electron.
▸ $Group$ : s-block $=$ valence $e^{-}$ ; p-block $=$ $10 +$ (valence $e^{-}$ ); d-block $=$ $(n - 1) d + n s$ electrons.
▸ $H$ ( $1 s^{1}$ ) is unique — placed with Group 1, but resembles Group 17 too; $He$ ( $1 s^{2}$ ) sits in Group 18.

🚫 Examiner Trap · Examiner traps

(1) Block

=

sub-shell that gets the LAST electron; Period

=

highest n. (2) d-block is

(n - 1) d

, f-block is

(n - 2) f

— mind the

n - 1

n - 2

. (3) p-block group

= 10 +

valence electrons. (4) H (

1 s^{1}

) is anomalous (Group 1 but resembles 17); He is in Group 18 despite

s^{2}

Types of Elements & Nomenclature

Metals, non-metals & metalloids

▸ $Metals$ (>78%): left & centre; lustrous, malleable, ductile, good conductors (exceptions: Hg liquid; Ga, Cs low m.p.).
▸ $Non-metals$ : top-right; brittle, poor conductors (C, B exceptions).
▸ $Metalloids$ (Si, Ge, As, Sb, Te): along the zig-zag border, intermediate properties.
▸Metallic character $↑$ down a group, $↓$ across a period.

Four types of elements:

Representative

(main-group: s- and p-blocks),

transition

(d-block, bridge metals),

inner-transition

(f-block lanthanoids & actinoids), and

noble gases

(Group 18, filled

n s^{2} n p^{6}

Digit	Root	Digit	Root
0	nil (n)	5	pent (p)
1	un (u)	6	hex (h)
2	bi (b)	7	sept (s)
3	tri (t)	8	oct (o)
4	quad (q)	9	enn (e)

🎯 Exam · IUPAC naming for

Z > 100

Spell the digits of Z using the roots, add

-ium

, and combine the symbols. E.g.

Z = 120

120 \to

un-bi-nil-ium

= unbinilium (Ubn)

;

Z = 117 \to

ununseptium (Uus).

🚫 Examiner Trap · Examiner traps

(1) Metalloids (Si, Ge, As, Sb, Te) lie on the zig-zag border. (2) Metallic character

↑

down a group,

↓

across a period. (3) IUPAC

Z > 100

: spell digits (un-bi-nil...)

+

ium (

Z = 120 \to

unbinilium Ubn). (4) Noble gases (

n s^{2} n p^{6}

) are a separate type, not 'non-metals' for trends.

Atomic & Ionic Radii

Compass showing that across a period ionization energy, electronegativity, electron gain enthalpy magnitude and non-metallic character rise while atomic radius and metallic character fall; down a group radius and metallic character rise while ionization energy and electronegativity fall — Master compass of the periodic trends.

Atomic radius: Half the internuclear distance between bonded atoms:

covalent radius

for non-metals (Cl–Cl

= 198

\Rightarrow

99 pm),

metallic radius

for metals (Cu–Cu

= 256

\Rightarrow

128 pm). Noble gases use the larger

van der Waals

radius.

Size trends

▸ $Across a period$ : radius $↓$ (effective nuclear charge rises, same shell).
▸ $Down a group$ : radius $↑$ (new shells; inner electrons shield).
▸ $Cation$ $<$ parent atom (fewer $e^{-}$ , same charge); $anion$ $>$ parent atom (added $e^{-}$ , more repulsion).
▸ $Isoelectronic$ species: radius $↓$ as nuclear charge $↑$ ( $O^{2 -} > F^{-} > N a^{+} > M g^{2 +} > A l^{3 +}$ ).

🚫 Examiner Trap · Examiner traps

(1) Radius

↓

across a period (

Z_{eff} ↑

↑

down a group (new shell). (2) Cation

<

parent atom; anion

>

parent atom. (3)

Isoelectronic

species: radius

↓

as nuclear charge

↑

(

O^{2 -} > F^{-} > N a^{+} > M g^{2 +} > A l^{3 +}

). (4) Noble gases use the larger van der Waals radius — don't compare directly.

Ionization Enthalpy

Ionization enthalpy (

Δ_{i} H

): The energy needed to remove the most loosely bound electron from an isolated gaseous atom in its ground state:

X (g) \to X^{+} (g) + e^{-}

. Always positive;

Δ_{i} H_{2} > Δ_{i} H_{1}

(harder to pull an

e^{-}

from a cation).

First ionization enthalpy rising across Period 2 from lithium to neon, with dips where beryllium exceeds boron and nitrogen exceeds oxygen — $Δ_{i} H_{1}$ rises across a period, with two notable dips.

Trends & their causes

▸ $Across a period$ : $Δ_{i} H ↑$ (nuclear charge rises, shielding nearly constant).
▸ $Down a group$ : $Δ_{i} H ↓$ (electron farther out, more shielding).
▸Depends on $Z_{eff}$ , shielding/screening and penetration ( $s > p > d > f$ ).

Successive ionization energies of sodium, with a small first value and a huge jump at the second electron where the neon core is broken — A sudden jump marks the start of a new (core) shell — here Na has 1 valence $e^{-}$ .

⚠️ Watch out · Two classic anomalies

Be > B

: removing B's

2 p

electron (shielded by

2 s

) is easier than Be's penetrating 2s.

N > O

: N has a stable half-filled

2 p^{3}

; O's fourth

2 p

electron is paired and feels extra repulsion.

🚫 Examiner Trap · Examiner traps

(1)

Δ_{i} H

is ALWAYS positive;

Δ_{i} H_{2} > Δ_{i} H_{1}

. (2) IE

↑

across,

↓

down. (3) Anomalies:

Be > B

(B's

2 p

is shielded) and

N > O

(N has stable half-filled

2 p^{3}

). (4) A sudden jump in successive IE marks the start of a noble-gas core — it locates the valence electrons.

Electron Gain Enthalpy & Electronegativity

Electron gain enthalpy (

Δ_{e g} H

): The enthalpy change when an electron is added to a neutral gaseous atom:

X (g) + e^{-} \to X^{-} (g)

. Usually negative (energy released); the more negative, the greater the tendency to form an anion.

Left: bar chart of halogen electron gain enthalpies, most negative, with chlorine more negative than fluorine. Right: electronegativity rising across Period 2 to fluorine at 4.0 on the Pauling scale — Halogens have the most negative $Δ_{e g} H$ ; electronegativity peaks at F.

Electronegativity: The tendency of an atom to attract the

shared

electron pair in a bond. It is a relative (not measurable) quantity; the

Pauling scale

sets F

= 4.0

, the highest.

Element	$Δ_{e g} H$ (kJ/mol)	EN (Pauling)
F	$- 328$	$4.0$
Cl	$- 349$	$3.0$
O	$- 141$	$3.5$
S	$- 200$	$2.5$

Trends & anomalies

▸ $Δ_{e g} H$ becomes $more negative$ across a period, $less negative$ down a group.
▸ $Anomaly$ : $Cl < F$ and $S < O$ (added $e^{-}$ crowds the compact $n = 2$ shell).
▸Noble gases have $positive$ $Δ_{e g} H$ (electron must enter a new shell).
▸Electronegativity $↑$ across, $↓$ down — it tracks non-metallic character.

🚫 Examiner Trap · Examiner traps

(1)

Δ_{e g} H

is usually negative (energy released); more negative

=

stronger anion-former. (2) Anomaly:

Cl > F

and

S > O

in magnitude (small

n = 2

shell crowds the added electron). (3) Noble gases have

positive

Δ_{e g} H

. (4) Electronegativity is RELATIVE (not measurable); F

= 4.0

is the highest; EN

↑

across,

↓

down.

Periodicity of Valence & Chemical Properties

Valence & oxidation states

▸ $Valence$ of a representative element $=$ number of valence electrons, or $8 -$ that number.
▸Group 1→18 valence: $1, 2, 3, 4, 3, 2, 1, 0$ .
▸d- and f-block elements show $variable$ oxidation states.
▸Reactivity is highest at the two $extremes$ (alkali metals lose $e^{-}$ , halogens gain $e^{-}$ ) and lowest in the centre.

Group	Valence	Oxide	Nature
1	1	$N a_{2} O$	basic
2	2	$MgO$	basic
13	3	$A l_{2} O_{3}$	amphoteric
15	5	$P_{4} O_{10}$	acidic
17	7	$C l_{2} O_{7}$	acidic

🎯 Exam · Second-period anomalies & diagonal relationship

The first element of each group (Li, Be, B…) differs from its heavier congeners — small size, high charge/radius ratio, and only

four

valence orbitals (no d). It resembles the second-period element of the

next

group:

Li-Mg, Be-Al, B-Si

(the diagonal relationship).

🚫 Examiner Trap · Examiner traps

(1) Valence of a main-group element

=

valence electrons OR

8 -

that. (2) Oxides go

basic \to amphoteric \to acidic

across a period (N

a_{2}

\to

l_{2}

O_{3}

\to

l_{2}

O_{7}

). (3) Reactivity is highest at the EXTREMES (alkali metals, halogens), lowest in the centre. (4) Diagonal relationship: Li–Mg, Be–Al, B–Si (2nd-period anomaly).

More JEE Main Chemistry formula sheets

Frequently Asked Questions

What are the most important Classification of Elements & Periodicity formulas for JEE Main?

This Classification of Elements & Periodicity formula sheet covers all the high-yield Chemistry formulas, definitions and theorems you need for JEE Main, across Modern periodic law, Present form of periodic table, s, p, d and f block elements, Periodic trends in properties, Atomic and ionic radii — each shown with the key result and, where useful, a worked example.

Is this Classification of Elements & Periodicity formula sheet free?

Yes — the full chapter formula sheet is free to read online, no login or payment required.

How should I revise Classification of Elements & Periodicity formulas?

Blurt the Classification of Elements & Periodicity formulas from memory, then check against this sheet to find your gaps — and practise a few previous-year questions on the chapter to make sure you can apply them under time pressure.

Also useful: all formula sheets · JEE Main previous-year papers · most important chapters.