Chapter: Atomic Structure & Laws
Which one of the following is the correctmolecular formula of ammonium carbonateif the valency of ammonium ion is (+1) andcarbonate anion is (–2)?
The molecular formula of a compound is determined by the valence (or charge) of its constituent ions. For ammonium (NH₄⁺) and carbonate (CO₃²⁻), balancing their charges yields the formula.
Given:
The charges must be balanced in the compound:
Let x = number of ammonium ions and y = number of carbonate ions:
This means:
The final molecular formula is:
Remember: "Ammonium and Carbonate, pair them to get rates!" For charge balancing, always cross-multiply the valencies.
A diagram illustrating the balance of charges between the ammonium and carbonate ions, showing one carbonate ion attracting two ammonium ions to form the compound.
Verified against NCERT Class XI Chemistry, Chapter on States of Matter.
Which one of the following is the correct orderof the valencies of elements Ne, Si, N and Mg?
The valency of an element signifies its ability to bond with other elements, often reflecting the number of electrons an atom can gain, lose, or share. Noble gases like Neon have a full outer shell, resulting in a valency of 0.
Thus, synthesizing these valencies gives the order: Ne < Mg < N < Si.
Option B: Incorrect, as it claims Si has a lower valency than N and Mg. Option C: Incorrect, as it misplaces Ne in the order. Option D: Incorrect, placing Mg inaccurately relative to Ne and N.
Remember: Noble gases are inert; Metals lose, Nonmetals gain! Valency acronym: N < Mg < Si < Ne.
Consider a periodic table highlighting the noble gases in green and their respective valencies with arrows indicating electron loss or gain.
Verified against NCERT Class XI Chemistry Chapter on Chemical Bonding and Molecular Structure.
Which of the following anions has a valency of –3?
The valency of an ion indicates its capacity to combine with other ions, specifically the number of electrons gained (for anions) to reach stability. The nitride ion (N³⁻) has a valency of -3, indicating it has accepted three electrons.
Nitrogen (N) has an atomic number of 7 and an electron configuration of 1s² 2s² 2p³. To achieve a stable octet, nitrogen needs to gain three electrons.
This reaction shows nitrogen gaining three electrons to form the nitride ion with a charge of -3.
Remember: "Nitrate's one, Sulfate's two, but Nitride is the three!" This phrase helps quickly recall the valency of these anions.
A diagram illustrating the electron configuration of nitrogen and the formation of the nitride ion would help visualize how three electrons are gained to achieve a valency of -3.
Verified against NCERT Class X Chemistry, Chapter 4 (Structure of Atom).
Which one of the following has the valency of 3?
The valency of an element is the number of electrons it can lose, gain, or share to achieve a stable electronic configuration, typically achieving an octet.
Elements have distinct valencies based on their group in the periodic table:
Nitrogen's electronic configuration is \( 1s^2 2s^2 2p^3 \), allowing it to share or gain three electrons to achieve a full octet. This is represented in the reaction with hydrogen:
Option A: Carbon - Valency of 4, forms four bonds.
Option B: Oxygen - Valency of 2, forms two bonds.
Option D: Sodium - Valency of 1, forms one bond.
Mnemonic: "Cathy Likes Nitrogen Soup" - Carbon (4), Lithium (1), Nitrogen (3), Sodium (1).
A comparison table illustrating elements, their group numbers, and their respective valencies would provide clarity.
Verified against NCERT Class 11 Chemistry, Chapter 3 (Classification of Elements).
For aluminium (Al) (atomic number: 13, massnumber: 27), which one of the following statements is NOT correct?
The valency of an element is determined by its ability to lose, gain, or share electrons in chemical reactions. For aluminium (Al), the electronic configuration supports a valency of +3.
Given:
Aluminium electron configuration:
Valency Calculation:
Aluminium has three valence electrons (2 in 3s and 1 in 3p) allowing its ionization to a stable +3 ion.
Remember: "Aluminium loses three" to recall Al's valency of +3.
A periodic table highlighting aluminium's position, showing its electron configuration and valency to illustrate its chemical behavior and stability.
Verified against NCERT Class 10 Science, Chapter 4 (Chemical Substances - Nature & Behaviour).
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