Updated By SaraNextGen

On April 21, 2024, 11:35 AM

Question 4.1:

Explain the formation of a chemical bond.

Answer:

A chemical bond is defined as an attractive force that holds the constituents (atoms, ions etc.) together in a chemical species.

Various theories have been suggested for the formation of chemical bonds such as the electronic theory, valence shell electron pair repulsion theory, valence bond theory, and molecular orbital theory.

A chemical bond formation is attributed to the tendency of a system to attain stability. It was observed that the inertness of noble gases was because of their fully filled outermost orbitals. Hence, it was postulated that the elements having incomplete outermost shells are unstable (reactive). Atoms, therefore, combine with each other and complete their respective octets or duplets to attain the stable configuration of the nearest noble gases. This combination can occur either by sharing of electrons or by transferring one or more electrons from one atom to another. The chemical bond formed as a result of sharing of electrons between atoms is called a covalent bond. An ionic bond is formed as a result of the transference of electrons from one atom to another.

Question 4.2:

Write Lewis dot symbols for atoms of the following elements: Mg, Na, B, O, N, Br.

Answer:

Mg: There are two valence electrons in Mg atom. Hence, the Lewis dot symbol for Mg is: 

Na: There is only one valence electron in an atom of sodium. Hence, the Lewis dot structure is: 

B: There are 3 valence electrons in Boron atom. Hence, the Lewis dot structure is: 

O: There are six valence electrons in an atom of oxygen. Hence, the Lewis dot structure is: 

N: There are five valence electrons in an atom of nitrogen. Hence, the Lewis dot structure is: 

Br: There are seven valence electrons in bromine. Hence, the Lewis dot structure is: 

Question 4.3:

Write Lewis symbols for the following atoms and ions:

S and S^2–; Al and Al³⁺; H and H^–

Answer:

(i) S and S^2–

The number of valence electrons in sulphur is 6.

The Lewis dot symbol of sulphur (S) is  .

The dinegative charge infers that there will be two electrons more in addition to the six valence electrons. Hence, the Lewis dot symbol of S^2– is  .

(ii) Al and Al³⁺

The number of valence electrons in aluminium is 3.

The Lewis dot symbol of aluminium (Al) is .

The tripositive charge on a species infers that it has donated its three electrons. Hence, the Lewis dot symbol is  .

(iii) H and H^–

The number of valence electrons in hydrogen is 1.

The Lewis dot symbol of hydrogen (H) is  .

The uninegative charge infers that there will be one electron more in addition to the one valence electron. Hence, the Lewis dot symbol is  .

Question 4.4:

Draw the Lewis structures for the following molecules and ions:

H₂S, SiCl₄, BeF₂, , HCOOH

Answer: