JEE Chapter - Classification of Elements and Periodicity in Properties

The periodic table is a tabular arrangement of chemical elements that is arranged by electron configurations, atomic number (number of protons in the nucleus), and recurrent chemical properties. s-block, p-block, d-block, and f-block are four rectangular blocks shown in this table. Metals fall on the left-hand side of one row or period whereas non-metals fall on the right-hand side.

This chapter covers all of the trends in the physical and chemical properties of the elements in detail. Electron affinity, Electropositivity, Electronegativity, Aufbau Principle, and Ionisation Energy are some of the significant topics covered in this chapter. This is a crucial chapter for students who want to learn about chemistry and how to identify the properties of elements. The periodic properties have a low exam weighting, although it is an important chapter in the chemical topic.

JEE Main Chemistry Chapter-wise Solutions 2022-23 

Important Topics for Classification of Elements and Periodicity in Properties

• Modern Periodic Table

• Periodic Properties of Elements

Important Concepts in Classification of Elements and Periodicity in Properties

Periodic Table

• The periodic table is a grouping of elements that have similar properties.

• It's a representation of the periodic law in graphic form.
  Periodic Law: It claims that the properties of chemical elements are related to their atomic numbers in a predictable manner.

• The table is divided into four blocks, each of which is about rectangular in shape. 

• The table's rows are known as periods, and the columns are known as groups. 

• Chemical characteristics of elements in the same column of the periodic table are comparable.

• Nonmetallic character (holding their own electrons) increases from left to right throughout a period and from down to up across a group.

• While the metallic character (surrendering electrons to other atoms) increases in the opposite way across the periodic table.

Groups

• Groups refer to the 18 vertical columns.

• A family is made up of elements that belong to the same group and is usually titled after the initial number.

Periods

• Periods refer to the horizontal rows. 

• In the long version of the periodic table, there are seven periods.

Periodic Properties of Elements

Shielding or Screening Effect

• In a multi-electron atom, the nucleus attracts valence electrons whereas inner-shell electrons repel them.

• The valence-electron perceives less attraction from the nucleus as a result of the combined effect of these attractive and repulsive forces acting on it. The effect is known as shielding or screening.

Effective Nuclear Charge

• Denoted by z*.

• The following formula relates it to actual nuclear charge (Z):
  Z* = (Z - 𝜎), where 𝜎 is the given screening constant.

• When we proceed from left to right, we notice that the size of effective nuclear charge grows.

Variation of Ionisation Energy in Periodic Table

• As the atomic number of a group grows, the ionisation energy drops. With an increase in atomic number, the ionisation energy increases over time.

Electron Affinity and Electronegativity 

• Generally, the definition of Electron affinity is given as "the energy produced when an additional electron is added to a neutral gaseous atom." 

• The electron affinity increases from left to right in the period. 

• The ability of an atom in a compound to attract a pair of bound electrons to itself is referred to as electronegativity.

• Electronegativity grows from left to right over time. Because of the decrease in size and increase in nuclear charge, this is the case.

• As a result, alkali metals have the lowest value and halogens have the highest.

• The electronegativity of inert gases is 0.

• Electronegativity falls from top to bottom in a group. This is due to an increase in the size of the atoms.

Mulliken's Scale

• The average value of an atom's ionisation potential and electron affinity was defined by Mulliken as electronegativity.

• Electronegativity = (Ionisation Potential + Electron Affinity)/2.

Pauling Scale

• The Pauling electronegativity scale is the most extensively used. It is predicated on the presence of surplus bond energy.

• ΔE = Actual Bond Energy = -√(EA-A X EB-B).

Atomic Volume

• It is the volume occupied by one gramme of an element's atom.

• Atomic Volume = (Gram Atomic Weight)/(Density in Solid State).

• c.c./mole is the unit of atomic volume.

Density

• The density of elements in solid form fluctuates with their atomic numbers on a regular basis.

• Initially, the density increases gradually over time and reaches a maximum someplace for the centre members, before progressively diminishing.

Melting and Boiling Points

• The melting temperatures of the elements show considerable regularity as the atomic number increases.

Oxidation State (Oxidation Number, O.N.)

• The total number of electrons that an element in a compound appears to have gained or lost (negative and positive oxidation states, respectively) during the creation of that compound is known as its oxidation number.

Magnetic Properties

• The characteristics of individual atoms determine the magnetic properties of matter.

Solved Examples From the Chapter

Example 1: The third period of the p-block contains an element. Its outermost shell has 5 electrons. Predict the composition of the group. What is the number of unpaired electrons in it?

Solution: It is a member of the 15th group (P). It has three electrons that are not coupled.

Example 2: Recently, an element X with Z = 112 was found. Predict its electrical configuration and recommend which group it belongs to.

Solution: Rn 5f14 6d10 7s2 is the element. It is a member of the 12th group.

Solved Questions From the Previous Year Question Papers

Question 1: The first ionisation potential of Na is 5.1 eV. The value of electron gain enthalpy of Na+ will be?

(1) – 2.55 eV

(2) – 5.1 eV

(3) – 10.2 eV

(4) + 2.55 eV

Solution: 

• The minimal amount of energy necessary to remove an electron from an atom or molecule in the gaseous state is described by the ionisation energy of an atom or molecule. 

• However, the amount of energy released when an isolated gaseous atom accepts an electron to become a monovalent gaseous anion is known as electron gain enthalpy. H = -5.1 eV in this case.

• As a result, option (2) is the proper response.

Question 2: The order of increasing sizes of atomic radii among the elements O, S, Se, and As is?

(1) As < S < O < Se

(2) O < S < As < Se

(3) Se < S < As < O

(4) O < S < Se < As

Solution: 

• The size of atomic radii grows as you move from top to bottom. 

• The size reduces as you move from left to right. As a result, O < S < Se < As.

• Therefore, option (4) is the proper response.

Question 3: The radius of La3+ (atomic number of La = 57) is 1.06 A. Which one of the following given values will be closest to the radius of Lu3+ (atomic number of Lu = 71)?

(1) 40 A

(2) 1.06 A

(3) 0.85 A

(4) 1.60 A

Solution: 

• ∴ r = 1/Z is the atomic radius. 

• ∴ Z2/Z1 = r1/r2, i.e., the ratio of two atomic radii.

• ∴ 71/57 = 1.06/r2

• ∴ As a result, r2 = 1.0657/71 = 0.85.

• So, option (3) is the correct answer.

Practice Questions

Question 1: The screening effect of electrons in the s, p, d, and f orbitals of a given shell of an atom on the electrons in its outer shell is in which order:

(i) s > p > d > f

(ii) d > p > s > f

(iii) p < d > s > f

(iv) f < p > s > d

Answer: (i) s > p > d > f

Question 2: Which of the following is the right order of the following species' sizes:

(i) I > I+ > I–

(ii) I+ > I– > I

(iii) I > I– > I+

(iv) I– > I > I+

Answer: (iv) I– > I > I+

Question 3: Which of the following alternatives has an order of arrangement that does not match the property variation noted against it?

(i) Al3+ < Mg2+ < F– > Na+ (increasing ionic size)

(ii) Li > Na < Rb > K (increasing metallic radius)

(iii) I < Br < Cl < F (increasing electron gain enthalpy)

(iv) B < C < N < O (increasing first ionisation enthalpy)

Answer: (iii) I < Br < Cl < F (increasing electron gain enthalpy), and

(iv) Li < Na < K < Rb (increasing metallic radius) and

Conclusion

With the advancement of science, the periodic table continues to change. Only elements up to atomic number 94 occur in nature; to proceed farther, new elements have to be synthesised in the laboratory. The first 118 elements are now known, completing the first seven rows of the table, but chemical characterization of the heaviest elements is still required to ensure that their properties correspond to their placements.

It's unclear how far the table will extend beyond these seven rows, or whether the patterns from the known part of the table will persist into this uncharted territory. Some scientific debate rages on about whether some items in today's table are correctly positioned. There are many different representations of the periodic law, and whether or not there is an optimal form of the periodic table is a topic of debate.

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