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Variation of Atomic Radii and ionic radii - (Concept)

Comparison of the ionic radii and atomic radii

Variation in a Period

In moving from left to right in a period, the nuclear charge increases and the last electron enters into the same shell, thus the effective nuclear charge increases. Thus in this way, the atomic size decreases in the period.

Variation in a Group

In moving from top to bottom in a group, the number of shells increases due to which the atomic size increases.

The size of the cation is always smaller than its parent atom. In the case of cations, the number of electrons in the ion decrease and the nuclear charge remains the same, thus the effective nuclear charge increases and the size decreases.

The size of the cation decreases as effective nuclear charge increases
M⁺³ < M⁺² < M⁺ < M

The size of the anion is always greater than its parent atom. In the case of anions, the number of electrons in the ion increase and the nuclear charge remains the same, thus the effective nuclear charge decreases and the size increases.

M^-3 > M^-2 > M^- > M

Atomic Properties

Atomic properties are the physical properties of elements that are related to the atomic number of the elements. These properties can be divided into two categories:

Properties of individual atoms: These are the properties of individual atoms that are directly dependent on their electronic configurations. Some examples include ionisation enthalpy, electron gain enthalpy, screening effect, effective nuclear charge, etc.
Properties of the group of atoms: These are properties of the group of atoms together that are indirectly related to their electronic configurations. Some examples include the melting point, boiling point, the heat of fusion, density, etc.

The Screening effect or Shielding effect

The decrease in the force of attraction between the outer electrons and the nucleus due to the presence of inner electrons is called the screening effect or shielding effect. Actually, these inner electrons generate the repulsion between these inner electrons and the outer electrons due to which the net force of attraction between the nucleus and the outer electrons decreases.

Calculation of the screening effect

For ns or np orbital electrons

All electrons in the (ns, np) group contribute to 0.35 each to the screening effect constant. Except for 1s electrons which contribute by 0.30.
All electrons in (n-1) shell contribute by 0.85 each to the screening effect constant.
All electrons in (n-2) shell or lower contribute by 1.0 each to the screening effect constant.

For d- or f-electrons

All electrons in the (ns, np) group contribute to 0.35 each to the screening effect constant.
All the electrons in groups lower than (nd, nf) contribute by 1.0 each to the screening effect.

Effective Nuclear Charge

Due to the screening effect of the inner or the same shell electrons, the net force of attraction between the nucleus and the outer electrons decreases. This decreased force of attraction is known as effective nuclear charge. It is represented by Z*. Mathematically, it can be formulated as:

Z* = (Z- $\sigma$ ), where $\sigma$ is the screening effect constant.

In a period, the effective nuclear charge increases in moving from left to right.

II Period	Li	Be	B	C	N	O	F	Ne
Z	3	4	5	6	7	8	9	10
𝜎	1.7	2.05	2.40	2.75	3.10	3.45	3.80	4.15
Z*	1.3	1.95	2.60	3.25	3.90	4.55	5.20	5.85

In a group, the effective nuclear charge almost remains the same.

Group I	Li	Na	K	Rb	Cs
Z	3	11	19	37	55
𝜎	1.7	8.8	16.8	34.8	52.8
Z*	1.3	2.2	2.2	2.2	2.2

Isoelectronic species -

A series of atoms, ions and molecules in which each species contains the same number of electrons but a different nuclear charge.

$\mathrm{e.g.\:\:N^{3-},O^{2-},F^{-},Ne,Na^{+},Mg^{2+},Al^{3+}}$

Concepts List

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Exam	Chapter
JEE MAIN	Classification of Elements and Periodic table

A.	K⁺ > Cl^-
B.	Na < Na⁺
C.	Cl > Cl^-
D.	P³⁺ > P⁵⁺

A.	$Li^{+}\;$
B.	$\; B^{3+}\;$
C.	$\; O^{2-}\;$
D.	$\; F^{-}$

A.	Be²⁺
B.	Mg²⁺
C.	Ca²⁺
D.	Sr²⁺

A.	N > Ce > Eu > Ho
B.	Ho > N > Eu > Ce
C.	Eu > Ce > Ho > N
D.	Ce > Eu > Ho > N

A.	Shielding constant
B.	atomic number
C.	charge on nucleus
D.	both nuclear charge and shielding constant

A.	lesser nuclear charge and lesser first ionisation enthalpy
B.	greater nuclear charge and lesser first ionisation enthalpy
C.	greater nuclear charge and greater first ionisation enthalpy
D.	lesser nuclear charge and greater first ionisation enthalpy

A.	Nuclear Charge increases
B.	distance remains constant
C.	shielding effect constant
D.	All of these

A.	$Ce>Sn>Yb>Lu$
B.	$Sn>Ce>Lu>Yb$
C.	$Lu>Yb>Sn>Ce$
D.	$Sn>Yb>Ce>Lu$

A.	Increases as we move left to right in a period
B.	Increases down the group
C.	Both a & b
D.	decreases down the group

A.	The ionic radii decrease from O^2- to Al³⁺
B.	The ionic radii increase from O^2- to Al³⁺
C.	The ionic radii increase from O^2-to F^- and then decrease from Na⁺, Mg²⁺, Al³⁺
D.	The ionic radii decrease from O^2- to F^- and then increase from Na⁺, Mg²⁺, Al³⁺

A.	$\mathrm{Mg}^{2+}<\mathrm{Na}^{+}<\mathrm{F}^{-}<\mathrm{O}^{2-}<\mathrm{N}^{3-}$
B.	$\mathrm{Mg}^{2+}>\mathrm{Na}^{+}>\mathrm{F}^{-}>\mathrm{O}^{2-}>\mathrm{N}^{3-}$
C.	$\mathrm{Na}^{+}<\mathrm{O}^{2-}<\mathrm{N}^{3-}<\mathrm{Na}^{+}<\mathrm{Mg}^{2+}$
D.	$\mathrm{Na}^{+}>\mathrm{O}^{2-}>\mathrm{N}^{3-}>\mathrm{Na}^{+}>\mathrm{Mg}^{2+}$

A.	$(a) < (b)< (c)< (d)<(e)$
B.	$(c)< (b)< (a)< (d)< (e)$
C.	$(d)< (c)< (b)< (a)< (e)$
D.	$(b)< (c)< (d)< (a)< (e)$

A.	I > I⁺ > I^-
B.	I > I^- > I⁺
C.	I⁺ > I^- > I
D.	I^- > I > I⁺

A.	${Na}^{+}<{Mg}^{2+}<{Al}^{3+}< {Si}^{4+}$
B.	${Mg}^{2+}<{Na}^{+}<{Al}^{3+}< {Si}^{4+}$
C.	${Al}^{3+}<{Na}^{+}<{Si}^{4+}< {Mg}^{2+}$
D.	${Na}^{+}>{Mg}^{2+}>{Al}^{3+}> {Si}^{4+}$

A.	s-orbital
B.	p-orbital
C.	d-orbital
D.	f-orbital

A.	F>O>N
B.	N>O>F
C.	F>N>O
D.	N>F>O

A.	F>N>O
B.	O>N>F
C.	N>O>F
D.	F>O>N

A.	is x < y
B.	does not exist
C.	is x >y
D.	is x = y

A.	0.72 and 0.54
B.	0.85 and 0.99
C.	1.05 and 0.99
D.	0.68 and 0.72

A.	$\mathrm{F}^{-}>\mathrm{O}^{2-}>\mathrm{Na}^{+}>\mathrm{Mg}^{2+}$
B.	$\mathrm{O}^{2-}>\mathrm{F}^{-}>\mathrm{Na}^{+}>\mathrm{Mg}^{2+}$
C.	$\mathrm{Mg}^{2+}>\mathrm{Na}^{+}>\mathrm{F}^{-}>\mathrm{O}^{2-}$
D.	$\mathrm{O}^{2-}>\mathrm{F}^{-}>\mathrm{Mg}^{2+}>\mathrm{Na}^{+}$

A.	$\mathrm{Br}^{-}\text{and} \: \mathrm{Be}^{2+}$
B.	$\mathrm{Cl}^{-}\text{and} \:\mathrm{Li}^{+}$
C.	$\mathrm{S}^{2-}\text{and} \:\mathrm{K}^{+}$
D.	$\mathrm{O}^{2-}\text{and} \:\mathrm{Mg}^{2+}$

A.	Both (A) and (R) are true and (R) is the correct explanation of (A).
B.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
C.	(A) is true but (R) is false.
D.	(A) is false but (R) is true.

A.	$\mathrm{Mg}^{2+}<\mathrm{Na}^{+}<\mathrm{F}^{-}<\mathrm{O}^{2-}<\mathrm{N}^{3-}$
B.	$\mathrm{N}^{3-}<\mathrm{O}^{2-}<\mathrm{F}^{-}<\mathrm{Na}^{+}<\mathrm{Mg}^{2+}$
C.	$\mathrm{F}^{-}<\mathrm{Na}^{+}<\mathrm{O}^{2-}<\mathrm{Mg}^{2+}<\mathrm{N}^{3-}$
D.	$\mathrm{Na}^{+}<\mathrm{F}^{-}<\mathrm{Mg}^{2+}<\mathrm{O}^{2-}<\mathrm{N}^{3-}$

A.	$\mathrm{Na}^{+}<\mathrm{K}^{+}<\mathrm{Mg}^{2+}<\mathrm{Al}^{3+}$
B.	$\mathrm{Al}^{3+}<\mathrm{Mg}^{2+}<\mathrm{K}^{+}<\mathrm{Na}^{+}$
C.	$\mathrm{Al}^{3+}<\mathrm{Mg}^{2+}<\mathrm{Na}^{+}<\mathrm{K}^{+}$
D.	$\mathrm{K}^{+}<\mathrm{Al}^{3+}<\mathrm{Mg}^{2+}<\mathrm{Na}^{+}$

A.	It is smaller than $\mathrm{F}^{-}$and $\mathrm{N}$
B.	It is bigger than $\mathrm{O}^{2-}$ and $\mathrm{F}^{-}$
C.	It is bigger than $\mathrm{F}^{-}$and $\mathrm{N},$ but smaller than of $\mathrm{O}^{2-}$
D.	It is smaller than $\mathrm{O}^{2-}$ and $\mathrm{F}$ , but bigger than of $\mathrm{N}$

A.	${O^{2}}^{-} , F^{-} ,Na , {Mg^{2}}^{+}$
B.	$O^{-} , F^{-} , Na^{+} , {Mg^{2}}^{+}$
C.	${O^{2}}^{-} , F^{-} , Na^{+} , {Mg^{2}}^{+}$
D.	$O^{-} , F^{-} , Na , Mg^{+}$

A.	$O^{2-}\; \;$ $>$ $F^{-}$ $>$ $Na^{+}$ $>$ $Mg^{2+}$ $>$ $Al^{3+}$
B.	$Al^{3+}$ $>$ $Mg^{2+}$ $>$ $Na^{+}$ $>$ $F^{-}$ $>$ $O^{2-}\; \;$
C.	$Na^{+}$ $>$ $Mg^{2+}$ $>$ $Al^{3+}$ $>$ $O^{2-}\; \;$ $>$ $F^{-}$
D.	$Na^{+}$ $>$ $F^{-}$ $>$ $Mg^{2+}$ $>$ $O^{2-}\; \;$ $>$ $Al^{3+}$

A.	$O^{2-}< F^{-}< Na+< Mg^{2+}$
B.	$Na+< Mg^{2}+< F^{-}< O^{2-}$
C.	$Mg^{2}+< Na+< F^{-}< O^{2-}$
D.	$Mg^{2}+<O^{2-}< Na^{+}< F^{-}$

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Variation of Atomic Radii and ionic radii - (Concept)

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A.	$N^{3-}, O^{2-},F^{-} \: \: and \: \: Na^{+}$
B.	$N^{3-}, Li^{+},Mg^{2+} \: \: and \: \: O^{2-}$
C.	$F^{-},Li^{+}, Na^{+} \: \: and \: \: Mg^{2+}$
D.	$Li^{+},Na^{+},O^{2-} \: \: and \: \:F^{-}$

A.	$\begin{aligned} &\mathrm{K}^{+}>\mathrm{Ca}^{2+}>\mathrm{P}^{3-}>\mathrm{S}^{2-}>\mathrm{Cl}^{-} \\ \end{aligned}$
B.	$\mathrm{P}^{3-}>\mathrm{S}^{2-}>\mathrm{Cl}^{-}>\mathrm{K}^{+}>\mathrm{Ca}^{2+} \\$
C.	$\mathrm{Cl}^{-}>\mathrm{S}^{2-}>\mathrm{P}^{3-}>\mathrm{Ca}^{2+}>\mathrm{K}^{+} \\$
D.	$\mathrm{P}^{3-}>\mathrm{S}^{2-}>\mathrm{Cl}^{-}>\mathrm{Ca}^{2+}>\mathrm{K}^{+}$

A.	$\mathrm{S}^{2-}<\mathrm{Cl}^{-}<\mathrm{Ca}^{2+}<\mathrm{K}^{+}$
B.	$\mathrm{K}^{+}<\mathrm{S}^{2-}<\mathrm{Ca}^{2+}<\mathrm{Cl}^{-}$
C.	$\mathrm{Ca}^{2+}<\mathrm{K}^{+}<\mathrm{Cl}^{-}<\mathrm{S}^{2-}$
D.	$\mathrm{Cl}^{-}<\mathrm{Ca}^{2+}<\mathrm{K}^{+}<\mathrm{S}^{2-}$

A.	$\mathrm{Ba}^{2+}, \mathrm{Sr}^{2+}, \mathrm{K}^{+}, \mathrm{Ca}^{2+}$
B.	$\mathrm{Li}^{+}, \mathrm{Na}^{+}, \mathrm{Mg}^{2+}, \mathrm{Ca}^{2+}$
C.	$\mathrm{N}^{3-}, \mathrm{O}^{2-}, \mathrm{F}^{-}, \mathrm{S}^{2-}$
D.	$\mathrm{K}^{+}, \mathrm{Cl}^{-}, \mathrm{Ca}^{2+}, \mathrm{Sc}^{3+}$

A.	Both A and R are correct and R is the correct explanation of A
B.	A is correct but R is not correct
C.	A is not correct but R is correct
D.	Both A and R are correct but R is NOT the correct explanation of A

A.	$\mathrm{Yb}^{3+}<\mathrm{Pm}^{3+}<\mathrm{Ce}^{3+}<\mathrm{La}^{3+}$
B.	$\mathrm{N}^{3-}<\mathrm{O}^{2-}<\mathrm{F}^{-}$
C.	$\mathrm{Cl}^{+}<\mathrm{Cl}<\mathrm{Cl}^{-}$
D.	$Cl^{-}<S^{2-}<P^{3-}$

A.	(A) is false but (R) is true
B.	Both (A) and (R) are true but (R) is not the correct explanation of (A)
C.	(A) is true but (R) is false
D.	Both (A) and (R) are true and (R) is the correct explanation of (A)

A.	Principal quantum number (n)
B.	None of the factors because their size is the same
C.	Electron-electron interaction in the outer orbitals
D.	Nuclear charge (z)

A.	(B), (C) and (D) only
B.	(A), (B), (C) and (D)
C.	(C) and (D) only
D.	(A), (C) and (D) only

A.	The atomic size decreases
B.	atomic weight increase
C.	The atomic size increases
D.	(b ) and (c)