79.CHEMICAL BONDING (26)- Covalent Bonding(25) – Problems(2).

Q: Which of the following statements for bond angles (θ) in CH4 and CH2F2 molecules is true –
A] 
θ CH4  >  θ CH2F2

B] θ CH4 θ CH2F2

C] θ CH4 θ CH2F2

A: Both molecules are sp3 hybridized . We know that bond angle in methane is 109.5º . To predict the bond angle in difluoromethane i.e CH2Fmolecule , we apply Bent’s rule. Fluorine is more electronegative than hydrogen.So, The hybrid orbitals in F-C-F bond will have less s- character than in H-C-H bonds ( i.e less than 25%). We know that 701

∴As s- character decreases, the bond angle will decrease too. Therefore , the correct option is A.

Q: The electronegativity difference between the covalently bonded atoms is
A] Less than 0
B] 0-0.3
C] 0.3-1.7
D] Over 1.7

A: The electronegativity difference between covalent bond atoms is 0-0.3.If the electronegativity difference is higher, then electrons are accepted and donated , thus forming ions.So, ionic bonds are formed if electronegativity difference is more than 1.7.  For polar covalent bonds it is between 0.3-1.7. 

∴ The correct answer is B.

Q: What is the hybridization of sulphur in H2S?
A] sp
B] sp2
C] sp3
D] none of the above.

A: S is attached to two H’s and has two lone pair of electrons. So it is sphybridized. C .

Q:  The central  atom in  BrFhas — # of bonding pairs and — # of lone pair of electrons.
A] 5 – 1
B]7 – 0
C] 5- 0 
D]6- 1

A:  Bromine is the central atom and it has 7 valence electrons- two in 4s and five in 4p orbitals. It forms five bonds with 5 F’s and thus, it has one lone pair on it. 

791.jpg

Correct answer is A.

Q: What is the geometry of ozone (03)?
A]Linear
B] TBP
C] Trigonal planar
D]Tetrahedral

A: Oxygen has 6 valence electrons → 2s2 2p4 .The ozone molecule has a sp2 hybridised oxygen atom  and so it has trigonal planar symmetry. The two resonance structures of ozone are shown below – 

792.jpg

In the above figure, the octet of a all oxygen atoms is complete. However, the central oxygen atom has only 5 electrons (one lone pair + one each forming a double bond) ,instead of six .So it has a positive charge. The oxygen atom with 7 valence electrons (3 LP’s = 6 electrons + 1 electron which forms the single bond) has a negative sign on it.

Q: What is the hybridization in SiO?
A]
sp3d2
B]sp3
C]sp3d

D]sp2

A: Silica or silicon dioxide (SiO2)molecule is a special case as it has a giant covalent structure. Looking at the molecule , the structure can be –

793.jpg

But the molecule shows a different structure. The structure of silica is (SiO4)n. Silicon di oxide is very hard and has a very high melting point (1610 ºC) . These properties indicate that the structure is very stable and has very strong covalent bonds.

794.jpg

In the above structure, silicon is attached to four oxygen atoms and so is sp3 hybridised. Answer is B.

 

In the next post we start discussing a new theory, which explains formation of bonds in a very different way.

Be a perpetual student of life and keep learning..

Good day !

 

References and Further reading –

1.http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_21c/natural_environment/lithosphererev3.shtml

 

 

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