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Classification of Elements and Periodicity in Properties - Electronic Configuration of Elements and the Periodic Table

Grade 11CBSEChemistry

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

🔑Concepts

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The period number in the periodic table corresponds to the highest principal quantum number (nn) of the elements in that period.

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The maximum number of electrons that can be accommodated in a shell is given by 2n22n^2, which explains why the first period has 2 elements (1s21s^2) and the second has 8 elements (2s22p62s^2 2p^6).

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s-block elements: These include Group 1 (Alkali metals, ns1ns^1) and Group 2 (Alkaline earth metals, ns2ns^2). They are all reactive metals with low ionization enthalpies.

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p-block elements: These comprise Groups 13 to 18. Together with s-block elements, they are called Representative Elements. Their general outer shell configuration is ns2np1−6ns^2 np^{1-6}.

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d-block elements: These are Groups 3 to 12, known as Transition Elements. They are characterized by the filling of inner dd orbitals, with a general configuration of (n−1)d1−10ns0−2(n-1)d^{1-10} ns^{0-2}.

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f-block elements: These are the Lanthanoids and Actinoids (Inner Transition Elements), characterized by the filling of (n−2)f(n-2)f orbitals. General configuration: (n−2)f1−14(n−1)d0−1ns2(n-2)f^{1-14} (n-1)d^{0-1} ns^2.

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The group number for s-block elements equals the number of valence electrons. For p-block, it is 10+number of valence electrons10 + \text{number of valence electrons}. For d-block, it is the sum of electrons in (n−1)d(n-1)d and nsns subshells.

📐Formulae

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

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

General Electronic Configuration of d-block: (n−1)d1−10ns0−2\text{General Electronic Configuration of d-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-block: } (n-2)f^{1-14} (n-1)d^{0-1} ns^2

Group number (p-block)=10+number of valence electrons (ns+np)\text{Group number (p-block)} = 10 + \text{number of valence electrons } (ns + np)

💡Examples

Problem 1:

An element has the atomic number Z=17Z = 17. Predict its period, group, and block in the periodic table.

Solution:

  1. Write the configuration: 1s22s22p63s23p51s^2 2s^2 2p^6 3s^2 3p^5. 2. The highest n=3n = 3, so it belongs to Period 33. 3. The last electron enters the pp orbital, so it is in the p-block. 4. Group number = 10+valence electrons=10+(2+5)=1710 + \text{valence electrons} = 10 + (2 + 5) = 17.

Explanation:

The valence shell is the 3rd3^{rd} shell (n=3n=3), and the outer configuration 3s23p53s^2 3p^5 indicates it is a halogen.

Problem 2:

Identify the period and group for an element with electronic configuration [Ar]3d104s2[Ar] 3d^{10} 4s^2.

Solution:

  1. Highest n=4n = 4, so it belongs to Period 44. 2. The last electrons were filled in the dd subshell (3d3d), but the ss subshell is also involved in the valence. 3. Group number for d-block = (n−1)d electrons+ns electrons=10+2=12(n-1)d \text{ electrons} + ns \text{ electrons} = 10 + 2 = 12.

Explanation:

Since the 3d3d orbital is completely filled and the highest principal quantum number is 44, the element is Zinc (ZnZn), located in Group 12, Period 4.

Problem 3:

Predict the block and group of an element with atomic number Z=56Z = 56.

Solution:

  1. Configuration: [Xe]6s2[Xe] 6s^2. 2. Highest n=6n = 6, so Period 66. 3. Last electron enters ss orbital, so s-block. 4. Valence electrons = 22, so Group 22.

Explanation:

Barium (BaBa) has a valence configuration of 6s26s^2, placing it in the alkaline earth metals group.

Electronic Configuration of Elements and the Periodic Table Revision - Class 11 Chemistry CBSE