JEE Mains Chemistry · Classification of Elements and Periodicity

Electronegativity and Metallic Character

Electronegativity is an atom's pull on a shared electron pair; it rises across a period and falls down a group, and metallic character runs the opposite way, with metalloids along the border between them.

All Classification of Elements and Periodicity notes JEE Mains Chemistry strategy

Why this matters

Nineteen PYQs, all multiple choice, and four from 2026. Six rank electronegativity on the Pauling scale; eight rank metallic character or test why it changes; five classify elements as metals, non-metals or metalloids, or pick out a diagonal pair.

Concept 1 of 3: Electronegativity on the Pauling scale

Electronegativity tracks the same pull as ionization enthalpy: a small atom with a large nuclear charge holds shared electrons hardest. So it rises across a period, falls down a group, and fluorine tops the scale. It is not a fixed property of an isolated atom; it depends on what the atom is bonded to.

Definition

Across a period: increases. Down a group: decreases.
Fluorine is the most electronegative element (4.0), then oxygen (3.5).
Electronegativity is not measured directly and is not constant: it varies with the atom the element is bonded to and with its oxidation state.
The more electronegative atom takes the negative oxidation state: in $\mathrm{OF_2}$ oxygen is +2, in $\mathrm{Na_2O}$ it is −2.
Mg (1.2) is below Al (1.5); an order that puts Al below Mg is wrong.

Series	Pauling electronegativity	Trend
Period 2	Li 1.0, Be 1.5, B 2.0, C 2.5, N 3.0, O 3.5, F 4.0	Rises across
Period 3	Na 0.9, Mg 1.2, Al 1.5, Si 1.8, P 2.1, S 2.5, Cl 3.0	Rises across
Group 1	Li 1.0, Na 0.9, K 0.8, Rb 0.8, Cs 0.7	Falls down
Group 17	F 4.0, Cl 3.0, Br 2.8, I 2.5, At 2.2	Falls down
Group 13	B 2.0, Al 1.5, Ga 1.6, In 1.7, Tl 1.8	Falls from B to Al, then rises slightly Poor shielding by d and f electrons again: Ga, In and Tl are above Al.

Values from the Pauling scale; the trend, not the second decimal, is what the questions test.

Practice this conceptself-check · 4 quick reps

The same idea in a real exam question:

JEE Mains · 2025 · 2 Apr 2025 · Q110Moderate

Example 1 · Classification of Elements and Periodicity · Electronegativity and Metallic Character

Electronic configuration of four elements

A,B,C

and D are given below (A)

1{\text{ }s}^{2}2{\text{ }s}^{2}2p^{3}

(B)

1{\text{ }s}^{2}2{\text{ }s}^{2}2p^{4}

(C)

1{\text{ }s}^{2}2{\text{ }s}^{2}2p^{5}

(D)

1{\text{ }s}^{2}2{\text{ }s}^{2}2p^{2}

Which of the following is the correct order of increasing electronegativity (Pauling's scale) ?

Electronegativity is not a constant

Unlike ionization enthalpy, electronegativity belongs to an atom in a bond. The same element has different values in different compounds, so a statement that it depends on the bonded atom is correct.

Drill 5 more on electronegativity on the pauling scale

Concept 2 of 3: Metallic character and reactivity

A metal is an element that loses electrons easily. That needs a low ionization enthalpy, so metallic character is highest at the bottom left of the table and lowest at the top right. Reactivity is different: it is high at both ends of a period, because the left end loses electrons easily and the right end gains them easily.

Definition

Across a period: metallic character falls, non-metallic character rises.
Down a group: metallic character rises.
The cause is the rise in ionization enthalpy across a period and the electron gain enthalpy becoming more negative.
Reactivity is highest at the two ends of a period (alkali metals and halogens), lowest in the middle; it does not rise steadily from group 1 to group 18.
Oxides follow the same line: group 1 oxides are basic, group 17 oxides are acidic.

Compare	More metallic	Reason
Na and Mg	Na	Left of Mg in period 3
Mg and Al	Mg	Left of Al in period 3
Be and Mg	Mg	Below Be in group 2
K and Ca	K	Left of Ca in period 4
Be and Si	Be	Si is a metalloid; Be is a metal
N, P, O, S, Cl, F	P most, F least	P is lowest and furthest left; F is top right

Down and to the left means more metallic.

Practice this conceptself-check · 4 quick reps

The same idea in a real exam question:

JEE Mains · 2022 · 28 July 2022 · Q122Moderate

Example 2 · Classification of Elements and Periodicity · Electronegativity and Metallic Character

The correct decreasing order for metallic character is

Atomic radius is not always larger than ionic radius

A statement pairing a correct metallic order with "atomic radius is always greater than ionic radius" is half false: an anion is larger than its atom. Judge each statement on its own.

Drill 7 more on metallic character and reactivity

Concept 3 of 3: Metals, non-metals, metalloids and diagonal pairs

A zig-zag line in the p-block separates metals on the left from non-metals on the right. The elements along the line, the metalloids, are in between. Separately, an element in period 2 often behaves like the element one row down and one column right, because the two have similar size and charge density.

Definition

Metalloids: B, Si, Ge, As, Sb, Te.
Every d-block element is a metal; the p-block has metals, metalloids and non-metals.
Non-metals have higher ionization enthalpy and higher electronegativity than metals.
A highly reactive metal and a highly reactive non-metal give an ionic compound.
Metal oxides are generally basic and non-metal oxides generally acidic.
Diagonal pairs: Li–Mg, Be–Al, B–Si. Li–Na is a group pair, not a diagonal one.

Element	Z	Group	Class
B	5	13	Metalloid
Si	14	14	Metalloid
Ge	32	14	Metalloid
As	33	15	Metalloid
Sb	51	15	Metalloid
Te	52	16	Metalloid
I	53	17	Non-metal
Bi	83	15	Metal
Pb	82	14	Metal

The metalloids run diagonally from B down to Te; Bi and Pb below them are metals.

Practice this conceptself-check · 4 quick reps

The same idea in a real exam question:

JEE Mains · 2021 · Paper 6 · Q45Moderate

Example 3 · Classification of Elements and Periodicity · Electronegativity and Metallic Character

The characteristics of elements

X,Y

and

Z

with atomic numbers, respectively, 33, 53 and 83 are

Bismuth is a metal

As and Sb in group 15 are metalloids, but Bi below them is a metal. Group 15 runs the whole range: N and P are non-metals, As and Sb metalloids, Bi a metal.

Drill 4 more on metals, non-metals, metalloids and diagonal pairs

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Reference tables (3)

Electronegativity on the Pauling scale5 rows

Series	Pauling electronegativity	Trend
Period 2	Li 1.0, Be 1.5, B 2.0, C 2.5, N 3.0, O 3.5, F 4.0	Rises across
Period 3	Na 0.9, Mg 1.2, Al 1.5, Si 1.8, P 2.1, S 2.5, Cl 3.0	Rises across
Group 1	Li 1.0, Na 0.9, K 0.8, Rb 0.8, Cs 0.7	Falls down
Group 17	F 4.0, Cl 3.0, Br 2.8, I 2.5, At 2.2	Falls down
Group 13	B 2.0, Al 1.5, Ga 1.6, In 1.7, Tl 1.8	Falls from B to Al, then rises slightly Poor shielding by d and f electrons again: Ga, In and Tl are above Al.

Values from the Pauling scale; the trend, not the second decimal, is what the questions test.

Metallic character and reactivity6 rows

Compare	More metallic	Reason
Na and Mg	Na	Left of Mg in period 3
Mg and Al	Mg	Left of Al in period 3
Be and Mg	Mg	Below Be in group 2
K and Ca	K	Left of Ca in period 4
Be and Si	Be	Si is a metalloid; Be is a metal
N, P, O, S, Cl, F	P most, F least	P is lowest and furthest left; F is top right

Down and to the left means more metallic.

Metals, non-metals, metalloids and diagonal pairs9 rows

Element	Z	Group	Class
B	5	13	Metalloid
Si	14	14	Metalloid
Ge	32	14	Metalloid
As	33	15	Metalloid
Sb	51	15	Metalloid
Te	52	16	Metalloid
I	53	17	Non-metal
Bi	83	15	Metal
Pb	82	14	Metal

The metalloids run diagonally from B down to Te; Bi and Pb below them are metals.

Watch out for (3)

Electronegativity is not a constant
→ Electronegativity on the Pauling scale
Atomic radius is not always larger than ionic radius
→ Metallic character and reactivity
Bismuth is a metal
→ Metals, non-metals, metalloids and diagonal pairs

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