First Year Chemistry Chapter 6 Online Short Questions for 1st Year Chemistry Chapter 6 Chemical Bonding Preparation

Why the bond angles of H₂O and NH₃ are not 109.5° like that of CH₄, although O and N-atoms are sp³ —hybridized?

• Ans 1:

  Like CH₄, the molecules of H₂O and NH₃ are also AB₄ type molecules. Carbon, oxygen and nitrogen atoms undergo sp³ -hybridization. CH₄ is perfectly tetrahedral with the angle of 109.5°. In case of ammonia, there are three bond pairs and one lone pair. Lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion. Due to this reason, angle reduces to 107.5° In case of H₂O, there are two lone pairs on oxygen. Due to this increased repulsion of two lone pairs, the angle further reduces to 104.5°

Ionization energy of the element is the binding energy of the nucleus and the electron. Why is it measured when the atom is in the gaseous state?

• Ans 1: The outermost electrons are attracted by the nucleus. If the atom is closer to some other atom of its own kind or of different kinds, then the outermost electrons are being attracted or repelled by other species as well. In that situation, it is not possible to guess the forces of attractions within the nucleus and the outermost electron.

The melting points, boiling points, heat of vaporization and heat of sublimation of electrovalent compounds are higher as compared to those of covalent compounds. Why?

• Ans 1: Electrovalent or ionic compounds have high melting and boiling points due to the close packing of oppositely charged ions. The positively charged ions are surrounded by negatively charged ions and vice versa. That is why, they have very high melting points, boiling points, heat of vaporizations and heats of sublimation.

Dipole moment of CO₂ is zero but that of CO is 0.12 Debye. Why?

• Ans 1: CO₂ is linear molecule and the two dipoles cancel the effect of each other. In CO there is a single dipole directed from carbon to oxygen and it not cancelled.

Why CO₂ has linear structure?

• Ans 1: Carbon has four electros in the outermost orbitals. It makes two sigma and two pi-bonds with two oxygen atoms. It means that it has two double bonds. Caron has no lone pair in CO₂ is AB₂ type molecule having the linear structure.0=C=0.

The abnormality of bond length and bond strength in HI is less prominent than that of HCI. Give reason.

• Ans 1: Chlorine has higher electronegativity than iodine. So, the polarities of HCI and HI bonds are unequal. Therefore, abnormality of bond length and bond strength of HCI is more prominent than HI.

Why positively charged ions are mostly smaller in sizes than their neutral atoms?

• Ans 1: By the removal of electrons the cloud of outermost orbitals becomes thin. In this way, the remaining electrons are accommodated in smaller space. The nuclei have better attractive forces for them, and so the size are decreased as compared to the neutral atoms.

Solid sodium chloride does not conduct electricity, but, when electric current is passed through molten sodium chloride or its aqueous solution, electrolysis takes place. Give reason.

• Ans 1: In solid, NaCI, the oppositely charged ions are fixed at their positions. So they do not conduct electricity in the solid state. In the molten state or solution state the ions are free to move towards the respective electrodes.

Why the electron affinities of II-A are less then those of I-A?

• Ans 1: The elements of II-A have fulfilled outermost s-orbitals, so electron has to be accommodated in the higher orbitals. Their electron affinities are positive. The elements of I-A can accommodate incoming electron in partially filled s-orbital.

How does the electronegativity difference decide the nature of ionic bond?

• Ans 1: When the electronegativity difference between two bonded atoms is 1.7 or more than that, then the bond is said to be ionic, otherwise covalent. The % age of ionic character is more than 51% when the electronegativity difference is 1.7.

Why the atomic radii increase down the group?

• Ans 1: The number of shells increase along with the increasing shielding effect down the group. These two factors are dominant in increasing the sizes. no doubt, the nuclear charges are increased, but this is not a dominant factor.

Why positively charged ions are mostly smaller in sizes than their neutral atoms?

• Ans 1: By the removal of electrons the cloud of outermost orbitals becomes thin. In this way, the remaining electrons are accommodated in smaller space. The nuclei have better attractive forces for them, and so the size are decreased as compared to the neutral atoms.

Most of He elements of the periodic table attain the electronic configuration of inert gases during bond formation. Justify it.

• Ans 1: Inert gases are not reactive due to complete octet except He. Most of He s-and p-block elements may attain eight electrons in the outermost orbitals. They do so either by losing, gaining or sharing the electrons.

Why the bond angles of H₂O and NH₃ are not 109.5° like that of CH₄, although O and N-atoms are sp³ —hybridized?

• Ans 1:

  Like CH₄, the molecules of H₂O and NH₃ are also AB₄ type molecules. Carbon, oxygen and nitrogen atoms undergo sp³ -hybridization. CH₄ is perfectly tetrahedral with the angle of 109.5°. In case of ammonia, there are three bond pairs and one lone pair. Lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion. Due to this reason, angle reduces to 107.5° In case of H₂O, there are two lone pairs on oxygen. Due to this increased repulsion of two lone pairs, the angle further reduces to 104.5°

Why the lone pairs of electrons on an atom occupy greater space?

• Ans 1: The lone of electrons of the central atom is only attracted by the nucleus of the central atom. It creates more forces of repulsion due to nearness of nucleus and occupies greater space as compared to the bond pair.

How does the electronegativity difference decide the nature of ionic bond?

• Ans 1: When the electronegativity difference between two bonded atoms is 1.7 or more than that, then the bond is said to be ionic, otherwise covalent. The % age of ionic character is more than 51% when the electronegativity difference is 1.7.

• Ans 1:

Why the molecule of BF₃ is triangular planar?

• Ans 1: 'B' has three electrons in the outermost orbitals. It promotes the electron from 2s orbital to one of the 2p orbitals. Boron undergoes sp²' hybridization. Three sp² -hybridized orbitals lie in one plane and adjust themselves at angle of 120^°. There F atom make three sigma bonds which lie in one plane. So, the molecule of BF₃ is planar.

Why the electron affinities of II-A are less then those of I-A?

• Ans 1: The elements of II-A have fulfilled outermost s-orbitals, so electron has to be accommodated in the higher orbitals. Their electron affinities are positive. The elements of I-A can accommodate incoming electron in partially filled s-orbital.

How do you justify that all the bonds between I-A and II-A with VI-A and VII-A are not equally ionic?

• Ans 1: The I.E. values of the I-A are less than II-A and the E.A. of VII-A are greater than VI-A. So, the bond between I­A and VII-A should be ionic to a good extent. The bonds between II-A and VI-A should be poorly ionic. It means that all the above mentioned compounds are not equally ionic.