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Classification of Elements and Periodicity in Properties - Modern Periodic Law and the present form of Periodic Table

Grade 11CBSEChemistry

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Modern Periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers (ZZ). This was established by Henry Moseley, who showed that atomic number is a more fundamental property than atomic mass.

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The long form of the Periodic Table consists of 1818 vertical columns called 'Groups' and 77 horizontal rows called 'Periods'.

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Periodicity: The repetition of similar properties after certain regular intervals is due to the recurrence of similar valence shell electronic configurations.

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The period number corresponds to the highest principal quantum number (nn) of the elements in that period. For example, the 4th4^{th} period starts with Potassium (Z=19Z=19) where n=4n=4.

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Elements are classified into four blocks based on the orbital being filled: ss-block (Groups 11 and 22), pp-block (Groups 1313 to 1818), dd-block (Groups 33 to 1212), and ff-block (Lanthanoids and Actinoids).

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IUPAC Nomenclature for Z>100Z > 100: Names are derived directly from the atomic number using numerical roots (0=nil0 = nil, 1=un1 = un, 2=bi2 = bi, 3=tri3 = tri, 4=quad4 = quad, 5=pent5 = pent, 6=hex6 = hex, 7=sept7 = sept, 8=oct8 = oct, 9=enn9 = enn) and the suffix −ium-ium.

📐Formulae

ν=a(Z−b)\sqrt{\nu} = a(Z - b) (where ν\nu is the frequency of X-rays emitted, ZZ is the atomic number, and aa and bb are constants)

General electronic configuration of s-block: ns1−2\text{General electronic configuration of } s\text{-block: } ns^{1-2}

General electronic configuration of p-block: ns2np1−6\text{General electronic configuration of } p\text{-block: } ns^2 np^{1-6}

General electronic configuration of d-block: (n−1)d1−10ns0−2\text{General electronic configuration of } d\text{-block: } (n-1)d^{1-10} ns^{0-2}

General electronic configuration of f-block: (n−2)f1−14(n−1)d0−1ns2\text{General electronic configuration of } f\text{-block: } (n-2)f^{1-14} (n-1)d^{0-1} ns^2

💡Examples

Problem 1:

Predict the position (period and group) of an element with atomic number Z=38Z = 38 in the periodic table.

Solution:

The electronic configuration of the element with Z=38Z=38 is [Kr]5s2[Kr] 5s^2.

Explanation:

Since the highest principal quantum number is n=5n=5, the element belongs to the 5th5^{th} period. Because the valence electrons are in the ss-orbital (ns2ns^2), it belongs to the ss-block and specifically Group 22.

Problem 2:

What is the IUPAC name and symbol for the element with atomic number Z=120Z = 120?

Solution:

Name: Unbinilium, Symbol: UbnUbn.

Explanation:

Using IUPAC roots: 1=un1 = un, 2=bi2 = bi, 0=nil0 = nil. Combining them with the suffix −ium-ium gives 'Un-bi-nil-ium'. The symbol is derived from the first letter of each root: UU, bb, and nn.

Problem 3:

An element has the outer electronic configuration 3d54s13d^5 4s^1. Identify its block, period, and group.

Solution:

Block: dd-block, Period: 44, Group: 66.

Explanation:

The highest principal quantum number is n=4n=4, so the period is 44. The last electron enters the dd-orbital, so it is in the dd-block. For dd-block elements, Group number = (number of electrons in (n−1)d(n-1)d subshell + number of electrons in nsns subshell) = 5+1=65 + 1 = 6.

Modern Periodic Law and the present form of Periodic Table Revision - Class 11 Chemistry CBSE