7 Most SAQ’s of Classification of Elements – The Periodic Table Chapter in Class 10th Physical Science (TS/AP)

4 Marks

SAQ-1 : Second ionization energy of an element is higher than its first ionization energy. Why?

Introduction

Ionization energy, the energy required to remove an electron from an atom, is a key concept in chemistry. It’s crucial to comprehend why the second ionization energy is typically higher than the first to understand atomic behavior and bonding.

Explanation of Ionization Energies

1. First Ionization Energy:
   • Involves the removal of an electron from a neutral atom.
   • This electron is easier to remove as it is further from the nucleus and experiences less attraction.
2. Second Ionization Energy:
   • Entails the removal of an electron from a positively charged ion.
   • After losing one electron, the atom becomes a positive ion, leading to increased attraction between the nucleus and the remaining electrons.

Reason for Higher Second Ionization Energy

1. After the first electron is removed, the atom acquires a positive charge.
2. This positive charge enhances the attraction between the nucleus and the remaining electrons.
3. Consequently, more energy is required to remove a second electron from the positively charged ion.
4. This results in the second ionization energy being higher than the first.

Example

Mathematically represented as:

$$1st I.E < 2nd I.E < 3rd I.E$$

Summary

In summary, the second ionization energy of an element is higher than its first because the positively charged ion holds the remaining electrons more tightly. Grasping this concept is essential for delving into atomic properties and predicting atomic interactions.

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SAQ-2 : How does metallic character change when we move.

i) Down in a group. Ii) Across a period?

Introduction

The change in metallic character across the periodic table is key to understanding the chemical behavior of elements. We’ll explore how metallic character varies as we move down a group and across a period.

Metallic Character Change in the Periodic Table

1. Down a Group:
   • Definition: A group is a column of elements in the periodic table.
   • Change in Metallic Character: Increases as we move down.
   • Reason:
     • Increase in atomic size and addition of electrons to new energy levels.
     • Outer electrons are less attracted to the nucleus, making it easier to lose electrons.
   • Example: In Group 1, francium (Fr) is more metallic than lithium (Li).
2. Across a Period:
   • Definition: A period is a row of elements in the periodic table.
   • Change in Metallic Character: Decreases from left to right.
   • Reason:
     • Decrease in atomic size and addition of electrons to the same energy level.
     • Increased attraction between electrons and the nucleus makes it harder for atoms to lose electrons.
   • Example: In Period 3, sodium (Na) is more metallic than chlorine (Cl).

Summary

In conclusion, the metallic character increases as we move down a group due to new energy levels and increased atomic size. In contrast, it decreases as we move across a period from left to right, owing to a decrease in atomic size and increased nuclear charge. Understanding these trends is crucial for grasping the reactivity and bonding characteristics of different elements.

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SAQ-3 : Write the electronic configuration of Na⁺ and Cl^–

Introduction

Understanding the electronic configurations of ions is crucial for analyzing how atoms and ions interact, especially when atoms lose or gain electrons to form ions.

Electronic Configuration of Ions

1. Na⁺ (Sodium Ion):
   • Original Atom: Sodium (Na) with configuration 1s²2s²2p⁶3s¹.
   • Formation: Na⁺ is formed by the loss of one electron from a sodium atom.
   • Configuration of Na⁺: 1s²2s²2p⁶.
   • The configuration is stable, resembling the noble gas neon (Ne).
2. Cl⁻ (Chloride Ion):
   • Original Atom: Chlorine (Cl) with configuration 1s²2s²2p⁶3s²3p⁵.
   • Formation: Cl⁻ is formed by the gain of one electron by a chlorine atom.
   • Configuration of Cl⁻: 1s²2s²2p⁶3s²3p⁶.
   • This configuration is stable, similar to the noble gas argon (Ar).

Summary

In conclusion, the sodium ion (Na⁺) has an electronic configuration of 1s²2s²2p⁶, achieved by losing one electron to resemble neon. The chloride ion (Cl⁻) has a configuration of 1s²2s²2p⁶3s²3p⁶, gained by adding one electron, akin to argon. Understanding these configurations is essential for studying the chemical behavior of ions and their interactions.

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SAQ-4 : Why were Dobereiner, Newlands and Mendeleeff were not 100% successful in their classification of elements? Why is the modern table relatively a better classification? Predict the reason.

Introduction

Early attempts at classifying elements by scientists like Dobereiner, Newlands, and Mendeleeff had limitations due to their reliance on atomic weights. The modern periodic table, organizing elements by atomic numbers, overcomes these limitations and offers a more accurate system.

Early Classifications: Dobereiner, Newlands, Mendeleeff

1. Dobereiner’s Triads:
   • Grouped elements into triads based on similar chemical properties.
   • Relied on atomic weights, leading to inaccuracies.
2. Newlands’ Law of Octaves:
   • Arranged elements in order of increasing atomic weights.
   • Noted a repetition in properties every eighth element, effective only up to calcium.
3. Mendeleeff’s Periodic Table:
   • Also based on atomic weights, causing placement issues.
   • Predicted properties of some yet-to-be-discovered elements.

Limitations of Early Classifications

1. Based on Atomic Weights: Led to misplacements as atomic weights don’t always reflect accurate chemical properties.
2. Unable to Account for Later Discovered Elements: Systems lacked space for noble gases and other elements discovered later.

Modern Periodic Table: A Better Classification

1. Based on Atomic Numbers:
   • Ensures a unique identification for each element.
   • Eliminates ambiguity and is more consistent than earlier systems.
2. Accommodates All Known Elements: Inclusive of elements discovered post-early classification.
3. Predictive Power: Allows accurate predictions about element properties.

Summary

In conclusion, the early classification systems, though foundational, were limited by their dependence on atomic weights. The modern periodic table, utilizing atomic numbers, offers a more accurate, comprehensive, and predictive framework for understanding element properties and relationships.

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SAQ-5 : Observe the given table and answer the following questions.

SI. No.	Electron Configuration
1.	1s2 2s2 2p6 3s2 3p3
2.	1s2 2s2 2p6 3s2 3p6 4s2
3.	1s2 2s2 2p6 3s2 3p6

1.Mention the divalent element name.

2. Name the element belongs to 3rd period and VA Group.

1. Divalent Element Name
   • Element: Calcium (Ca)
   • Reason: Its electronic configuration ends with 4s², indicating two valence electrons. Calcium can lose these electrons to achieve stability, classifying it as a divalent element.
2. Element in the 3rd Period and VA Group
   • Element: Phosphorus (P)
   • Reason: Its electronic configuration ends with 3s² 3p³. This places it in the 3rd period and the VA group (Group 15) of the periodic table.

Summary

In conclusion, the electronic configurations provided allow us to identify Calcium as a divalent element and Phosphorus as belonging to the 3rd period and VA Group in the periodic table. Understanding electronic configurations is crucial for determining the properties and placements of elements within the periodic table.

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SAQ-6 : “Hydrogen occupies a unique positive in modern periodic table” Justify the statement.

Introduction

Hydrogen is an exceptionally unique element in the modern periodic table. Its distinct characteristics align it with multiple groups, leading to extensive discussions about its precise placement.

Similarity with Alkali Metals

1. Electron Configuration:
   • Hydrogen has one electron in its outermost shell, like alkali metals.
   • It can easily lose one electron, similar to alkali metals.
2. Formation of Positive Ions:
   • Hydrogen can lose an electron to form H+ ions, akin to alkali metals forming positive ions.

Similarity with Halogens

1. Electron Acceptance:
   • Hydrogen can gain an electron, resembling the behavior of halogens.
   • This leads to the formation of negative hydride ions (H−).
2. Existence as Diatomic Molecules:
   • Both hydrogen and halogens exist naturally as diatomic molecules (2H₂​).

Unique Position in the Periodic Table

Placed at the Top:
Hydrogen’s placement at the top of the periodic table reflects its dual resemblance to both alkali metals and halogens.

Summary

Hydrogen’s placement in the modern periodic table is justified by its similarity to both alkali metals and halogens. Its ability to both lose and gain an electron highlights its multifaceted nature, underscoring its special place in the periodic table. Understanding hydrogen’s position is crucial for comprehending its behavior and interactions with other elements.

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SAQ-7 : The atomic numbers of the elements belong to the modern periodic table are 20, 26. To which period and group these belongs to?

Introduction

In the modern periodic table, elements are systematically arranged based on their atomic numbers. This discussion focuses on the placement of elements with atomic numbers 20 (Calcium) and 26 (Iron).

Element with Atomic Number 20 (Calcium – Ca)

1. Atomic Number: 20
2. Group: 2 (Alkaline Earth Metals)
3. Period: 4
4. Explanation:
   • Calcium has two electrons in its outermost shell.
   • Placed in Group 2, consisting of elements with two electrons in their outermost shell.
   • Located in the fourth period, indicating four energy levels or shells.

Element with Atomic Number 26 (Iron – Fe)

1. Atomic Number: 26
2. Group: 8 (Transition Metals)
3. Period: 4
4. Explanation:
   • Iron is a transition metal, placed in Group 8.
   • Similar to calcium, iron is in the fourth period, having four energy levels or shells.

Summary

In conclusion, Calcium (atomic number 20) belongs to Group 2 and Period 4, while Iron (atomic number 26) is in Group 8 and Period 4 of the modern periodic table. The understanding of an element’s placement in the periodic table is essential for studying its properties and behavior in various chemical reactions.