Topic: Chemical Bonding and Molecular Structure (Test 1)



Topic: Chemical Bonding and Molecular Structure
Q.1
Octet of electrons, represents a particularly stable electronic arrangement.. Atoms achieve the stable octet when they are linked by chemical bonds. This rule is associated with one of the following theories
A. Valence Bond (VB) Theory
B. Lewis approach
C. Valence Shell Electron Pair Repulsion VSEPR Theory
D. Molecular Orbital (MO) Theory
Answer : Option B
Explaination / Solution:

Lewis developed electronic theory of valence or theory of chemical bonding to explain the formation of chemical bond between the two atoms.

According to the electronic theory of valence, every atom tries to attain octet configuration (presence of eight electrons) in its valence shell by losing or gaining or by sharing of electrons. This is known as the "Octet Rule".

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by Counterflix

The electrostatic forces of attraction that holds the two oppositely charged ions together are known as "electrovalent bond".


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Q.2
Inertness of noble gas was observed to be due to their electronic configurations: Choose the most appropriate
A. Atomic mass is low so they are stable
B. Outermost orbitals of the noble gases are fully filled.
C. Noble gases form ions to complete their outermost orbitals
D. Total number of electrons in the outermost shell is duplets
Answer : Option B
Explaination / Solution:

The six noble gases (Helium Neon Argon Krypton Xenon Radon) are found in group 18 of the periodic table. These elements were considered to be inert gases until the 1960's, because their oxidation number of 0 prevents the noble gases from forming compounds readily. All noble gases have the maximum number of electrons possible in their outer shell (2 for Helium, 8 for all others), making them stable.

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Q.3
Stable outer octet of electrons is achieved in chlorine atom during the formation of NaCl by:
A. The formation of a coordinate bond
B. The loss of an electron
C. The formation of a hybrid orbital
D. The gain of an electron
Answer : Option D
Explaination / Solution:

Na lose its one electron forming Na+ while Cl gains the electron formimg Cl-

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Q.4
The bond formed, as a result of the electrostatic attraction between the positive and negative ions was termed as
A. electrovalent bond
B. covalent bond
C. coordinate bond
D. single covalency
Answer : Option A
Explaination / Solution:

Chemical bond formed between two atoms due to transfer of electron(s) from one atom to the other. atom is called "Ionic bond" or "electrovalent bond". in electrovalent bond one atom loses an electron to form a positive ion and the other atom gains the electron to form a negative ion. The resulting ions are held together by electrostatic attraction

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Q.5
The number of dots around the Lewis symbols for the elements represent
A. the number of valence electrons of the element
B. electrovalency
C. coordinate valency
D. group valence of the element
Answer : Option A
Explaination / Solution:

Gilbert N. Lewis is widely known for his use of simple symbolic representations of elements that show valence electrons as dots. The Lewis electron-dot symbols focus on the electrons in the highest principal energy level in the atom, the valence electrons. After all, these are the electrons that participate in chemical reactions. Lewis electron-dot symbols work well for the representative elements.

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Q.6

The formation of the Clmolecule can be understood in terms of the sharing of a pair of electrons between the two chlorine atoms, each chlorine atom contributing one electron to the shared pair. Choose the most appropriate name of the bond that is formed


A. double bond
B. multiple bond
C. ionic bond
D. a single covalent bond
Answer : Option D
Explaination / Solution:

Two chlorine atoms will each share one electron to get a full outer shell and form a stable Cl2 molecule. By sharing the two electrons where the shells touch each chlorine atom can count 8 electrons in its outer shell. These full outer shells with their shared electrons are now stable and the Cl2 molecule will not react further with other chlorine atoms. One pair of shared electrons form a single covalent bond.

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Q.7
When a gas phase atom in its ground state gains an electron. This is called
A. Electron affinity
B. electron gain enthalpy
C. lattice enthalpy
D. ionization enthalpy
Answer : Option B
Explaination / Solution:

Electron gain enthalpy (ΔegH) is defined as the enthalpy change associated with an isolated gaseous atom (X) when it gains an electron to form its corresponding anion. The reaction can be given as below:


On the basis of nature of the element, the process of accepting electron in an atom can either be exothermic or endothermic.


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Q.8
788 kJ of energy is required to separate one mole of solid NaCl into one mole of  (g) and one mole of (g) to an infinite distance. This process explains
A. Electron affinity
B. ionization enthalpy
C. lattice enthalpy
D. electron gain enthalpy
Answer : Option C
Explaination / Solution:

Lattice enthalpy is simply the change in Enthalpy associated with the formation of one mole of an ionic compound from its oppositely charged ions in their standard states under standard conditions.

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Q.9
A qualitative measure of the stability of an ionic compound is provided by
A. electron gain enthalpy
B. Electron affinity
C. lattice enthalpy
D. ionization enthalpy
Answer : Option C
Explaination / Solution:

Lattice energy is an estimate of the bond strength in ionic compounds. It is defined as the heat of formation for ions of opposite charge in the gas phase to combine into an ionic solid. The stability of ionic bond is directly propotional to lattice energy.

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Q.10
bond lengths are lower in elements having
A. triple bond
B. single bond
C. double bond
D. crystal structure
Answer : Option A
Explaination / Solution:

The bond length depends on the strength of the bond. The stronger the bond is, the shorter it will be. The triple bonds are the strongest and hence the shortest. Then comes double bonds which are of intermediate strength between the triple and single bonds. And finally the single bonds are weaker than the other two. This way, Triple bonds are the shortest. Then comes double bonds. Finally, single bonds are the longest among the three. The order of bond lengths is given as, Triple bond < Double bond < Single bond

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