Q3. - Organic Chemistry

Question

Question: How many covalent bonds are predicted for each atom? 

$a\mathit{.}\mathit{ }O\mathit{ }b\mathit{.}\mathit{ }Al\mathit{ }c\mathit{.}\mathit{ }Br\mathit{ }d\mathit{.}\mathit{ }Si$

Step-by-Step Solution

Answer

 Answer

a. The covalent bonds are predicted for O is 2.

 

b. The covalent bonds predicted for Al is 4.

 

c. The covalent bonds predicted for Br are 1, 3, 5, and 7.

 

d. The covalent bonds are predicted for Si are 4 and 7.

Step-by-Step Solution Step 1: Meaning of covalent bond

The bond that is formed by sharing of electrons is termed a covalent bond. The number of the covalent bonds depends upon the valence shell electron of an element.

Step 2: Calculation of covalent bonds in O

Oxygen’s atomic number is eight, and its electronic configuration is $1{\mathrm{s}}^{2}2{\mathrm{p}}^{2}2{\mathrm{p}}^4$ . The valence electrons in oxygen are six. That means it needs two electrons to complete its octet. Either it forms two single bonds or a double bond. 

 

For example: ${\mathrm{H}}_2\mathrm{O} \mathrm{and} {\mathrm{O}}_2$

Step 3: Calculation of covalent bonds in Al

 

The atomic number of Al is 13, and its electronic configuration is $1{\mathrm{s}}^{2}2{\mathrm{p}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^1$.

The valence electrons in Al is three. The maximum number of bonds it can form is the number of unpaired electrons in its valence shell, which is three. 

 

Thus, Al can form only three covalent bonds. Due to the incomplete octet, covalent Al compounds are generally called electron-deficient compounds and thus can act as Lewis acid. Further, they can accept one electron pair to form a coordinate covalent bond.

 

For example: ${\mathrm{AlCl}}_{3 }+ {\mathrm{Cl}}^{-} \to \mathrm{AlC}{{\mathrm{l}}_4}^{-}$

Thus, the number of covalent bonds are predicted for Al is 4.

Step 4: Calculation of covalent bonds in Br

The atomic number of Br is 35, and its electronic configuration is  $\left[\mathrm{Ar}\right] 3{\mathrm{d}}^{1}4{\mathrm{s}}^{2}4{\mathrm{p}}^5$

 

The atomic number of Br is 35, and its electronic configuration is  . The valence electrons in Br are seven. It needs only 1 electron to attain noble gas configuration. It is very easy for bromine to form a single bond.

 

Bromine belongs to the fourth period so it can expand its octet due to the presence of d-orbitals and there are several examples of bromine forming 3, 5, and 7 covalent bonds. 

For example:

 

$$\begin{gathered} \mathrm{HBr}, \mathrm{HOBr} (1-\mathrm{covalent} \mathrm{bond}) \\ {\mathrm{Br}}_3, {\mathrm{HBrO}}_2(3-\mathrm{covalent} \mathrm{bond}) \\ {\mathrm{BrF}}_5, {\mathrm{HBrO}}_3(5-\mathrm{covalent} \mathrm{bond}) \\ {\mathrm{HBrO}}_4(7-\mathrm{covalent} \mathrm{bond}) \end{gathered}$$

 

Thus, the number of covalent bonds are predicted for Br is 1, 3, 5, and 7.

Step 5: Calculation of covalent bonds in Si

Silicon’s atomic number is 14, and its electronic configuration is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^2$

In silicon, the valence electrons are four. It needs four electrons to attain a noble gas configuration.

 

Due to the presence of d-orbitals, it can expand its octet by accepting electrons pairs. Thus, it behaves like Lewis acid.

 

For example:

$$\begin{gathered} SiC{l}_{\mathit{4}}\mathit{,}Si{O}_{\mathit{2}}\mathit{(}\mathit{4}\mathit{-}\mathit{c}\mathit{o}\mathit{v}\mathit{a}\mathit{l}\mathit{e}\mathit{n}\mathit{t}\mathit{ }\mathit{b}\mathit{o}\mathit{n}\mathit{d}\mathit{)} \\ Si{{\mathit{F}}_{\mathit{6}}}^{\mathit{-}\mathit{2}}\mathit{(}\mathit{6}\mathit{-}\mathit{c}\mathit{o}\mathit{v}\mathit{a}\mathit{l}\mathit{e}\mathit{n}\mathit{t}\mathit{ }\mathit{b}\mathit{o}\mathit{n}\mathit{d}\mathit{)} \end{gathered}$$

Thus, the number of covalent bonds are predicted for Si is 4 and 7.