Chapter2 : Let us answer these (Page-35)

Q1. Using dots(.) and cross (X) to represent valence electrons, show the formation of covalent bonds in CO2 and CCL4 .
Ans: i) Formation of  CO2 molecule:

         ii) Formation of CCL4 molecule:

Q2. Why does carbon tetrachloride not conduct electricity?

Ans: Because it is made up of neutral molecule. So, there is no electron free to move. That is why it does not conduct electricity.

Q3. How does a co-ordinate bond differ from a normal covalent bond?

Ans: 

• In a covalent bond, both atoms are contributing same number of electrons to the bond, but in a coordinate covalent bond, two electrons are donated by a single atom.

• In a covalent bond, the electronegativity difference between the two atoms can be zero or a very low value, but in coordinate covalent bond, type of a polar covalent bond is forming.

• For a coordinate covalent bond to form, an atom in the molecule should have a lone pair.

Q4. Why does H2 molecule exist while He2 does not exist?

Ans: H₂ is formed due to combination of two hydrogen atoms. Atomic number of hydrogen is 1 .

Hence it’s electronic configuration is 1s¹.According to valence bond theory,halfilled atomic orbitals can overlap to form a bond.Thus two hydrogen atoms along with half filled 1s orbital,overlap with each other to form H₂ molecule. H₂ is formed dew to s-s overlap.

Whereas atomic number of helium is 2 .It’s electronic configuration is 1s².Filled orbital can not overlap and hence cannot form a bond.Hence diatomic helium i.e.He₂ molecule does not exist.

Q5. Why is HF polar while H2 and F2 are not polar?

Ans: This is because F is more electronegative than H, and therefore F attracts the electrons of H to itself. This results in a polar bond.H2 and F2 is non-polar as they are made of two same atoms which means both atoms should have the same electronegativity. Thus, an equal number of electrons exist in the orbital overlap.

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