Q: (a) Classify following oxides as neutral, acidic, basic or amphoteric:\$CO,\, B_2O_3,\, SiO_2,\, CO_2,\, Al_2O_3,\, PbO_2,\, Tl_2O_3\$(b) Write suitable chemical equations to show their nature.

The neutral oxide is CO. The acidic oxides are \$\displaystyle B_2O_3, SiO_2\$ and \$ CO_2\$.The basic oxide is \$\displaystyle Tl_2O_3 \$.The amphoteric oxides are \$\displaystyle Al_2O_3 \$ and \$PbO_2 \$.

Q: Ionisation enthalpy \$(\Delta _iH_1\ kJ \ mol^{-1})\$ for the elements of Group \$13\$ follows the order:

On moving down the group from \$B\$ to \$Tl\$, a regular decreasing trend in the I.E. is not observed.Element\$B\$\$Al\$\$Ga\$\$In\$\$Tl\$I.E. (kJ/mol) 801577579558589In Ga, there are ten d-electrons in the penultimate shell which screen the nuclear charge less effectively and thus, outer electron is held firmly. As a result, the ionisation energy of both Al and Ga is nearly the same. The increase in ionisation energy from In to Tl is due to poor screening effect of 14f electrons present in the inner shell.Thus, the correct order is, \$B>Al In<Tl\$

Q: \$CO_{2}\$ is gas, while \$SiO_{2}\$ is a solid at room temperatue. State a reason for it.

\$CO_2\$ consists of individual molecules with one central carbon atom double bonded to two oxygen atoms. Silicon does not form double bonds with oxygen.\$CO_2\$ is gas but \$SiO_2\$ is solid because the \$SiO_2\$ is in giant molecular structure but the \$CO_2\$ is simple molecular structure.Because of this reason \$CO_2\$ is gas but \$SiO_2\$ is solid.

Question 1

Why does carbon form such a large number of compounds?

Accepted Answer

Carbon is the only element that can form so many different compounds because each carbon atom can form four chemical bonds to other atoms and because the carbon atom is just the right, small size to fit in comfortably as parts of very large molecules. This property is called the catenation

Question 2

Explain why carbon forms compound mainly by covalent bonds. Explain in brief two main reasons for carbon forming a large number of compounds. Why does carbon form strong bonds with most other elements?

Accepted Answer

Carbon has 4 electrons in its outermost shell, and needs to gain or loss 4 electrons to attain nobel gas configuration. Losing or gaining 4 electrons is not possible due to energy considerations, hence it shares electrons to form covalent bonds.Two reasons for large number of carbon compounds:1) Catenation: The unique ability of carbon to form bonds with other atoms of carbon giving rise to long chains of different types of compounds.2) Tetravalency: since carbon has a valency of 4, it is capable of bonding with four other atoms of Carbon or atoms of elements like oxygen, hydrogen, nitrogen, sulphur, chlorine etc.Carbon forms strong bonds with most other elements because of its small size which enables the nucleus to hold on to the shared pairs of electrons strongly.

Question 3

What is inert pair effect?

Accepted Answer

Explanation:Inert pair effect can be defined as the reluctance of the outermost shell $s-$ electrons to participate in bonding.It is most commonly observed for group $4$ and group $5$ elements.The lower oxidation states of the elements of this group are formed due to the inert pair effect.Example: For $Sn$, there are two oxidation states $+2$ and $+4$. Out of these, $Sn^{2+}$ is formed due to the inert pair effect, where the valence shell $s-$ electrons remain paired instead of participating in bond formation.

Question 4

(a) Classify following oxides as neutral, acidic, basic or amphoteric:$CO,\, B_2O_3,\, SiO_2,\, CO_2,\, Al_2O_3,\, PbO_2,\, Tl_2O_3$(b) Write suitable chemical equations to show their nature.

Accepted Answer

The neutral oxide is CO. The acidic oxides are $\displaystyle B_2O_3, SiO_2$ and $ CO_2$.The basic oxide is $\displaystyle Tl_2O_3 $.The amphoteric oxides are $\displaystyle Al_2O_3 $ and $PbO_2 $.

Question 5

Ionisation enthalpy $(\Delta _iH_1\ kJ \ mol^{-1})$ for the elements of Group $13$ follows the order:

Accepted Answer

On moving down the group from $B$ to $Tl$, a regular decreasing trend in the I.E. is not observed.Element$B$$Al$$Ga$$In$$Tl$I.E. (kJ/mol) 801577579558589In Ga, there are ten d-electrons in the penultimate shell which screen the nuclear charge less effectively and thus, outer electron is held firmly. As a result, the ionisation energy of both Al and Ga is nearly the same. The increase in ionisation energy from In to Tl is due to poor screening effect of 14f electrons present in the inner shell.Thus, the correct order is, $B>AlIn

Question 6

Explain the difference in properties of diamond and graphite on the basis of their structures.

Accepted Answer

The difference between diamond and carbon is given below. DiamondGraphite  It has crystalline natureIt has layered structure  Each C is $\displaystyle sp^3 $ hybridzed and forms 4 covalent bonds with neighboring C atoms. Each C atom is $\displaystyle  sp^2$  hybridized and forms 3 sigma bonds with 3 other C atoms. Fourth electron forms pi bond. The geometry is tetrahedral.The geometry is planar  C-C bond length is 154 pmC-C bond length is 141.5 pm  It has rigid covalent boning which is difficult to break.It is soft. Its layers can be separated easily.  It is an electrical insulator.It is good conductor of electricity.

Question 7

$CO_{2}$ is gas, while $SiO_{2}$ is a solid at room temperatue. State a reason for it.

Accepted Answer

$CO_2$ consists of individual molecules with one central carbon atom double bonded to two oxygen atoms. Silicon does not form double bonds with oxygen.$CO_2$ is gas but $SiO_2$ is solid because the $SiO_2$ is in giant molecular structure but the $CO_2$ is simple molecular structure.Because of this reason $CO_2$ is gas but $SiO_2$ is solid.

Question 8

The hybridization of carbon in diamond, graphite and acetylene is respectively:

Accepted Answer

In diamond, each carbon combine with 4 other carbon atoms with four sigma bonds. Hence, the hybridization of carbon is $sp^3$.In graphite, each carbon combines with 3 other carbon atoms with three sigma bonds. so $sp^2$ hybridization.In acetylene, one carbon combines with another carbon atom with three bonds (1 sigma and 2 pi bonds). so $sp^2$ hybridization.The hybridisation of carbon atom in diamond, graphite and acetylene are respectively $sp^3,\ sp^2,\ sp$Hence, option C is correct.

Question 9

What are the two properties of carbon which lead to the formation of a large number?

Accepted Answer

The two properties that give rise to carbon to form a large number of compounds are:1) Catenation: It is the ability to form bonds with other carbon atoms.2) Tetravalency: Due to 4 valency of carbon, it is capable of bonding with four other atoms.

Question 10

Explain: (i) ${[Si{F}_{6}]}^{2-}$ is known whereas ${[Si{Cl}_{6}]}^{2-}$ is not known.(ii) Boron is unable to form ${[{BF}_{6}]}^{3-}$ ion(iii) conc. $H{NO}_{3}$ can be stored in Aluminium container.

Accepted Answer

a)Due to smaller size of F as compared  to Cl , six small F atoms can be easily accommodated  around Si atom while Cl cannot since F are present in smaller 2p orbital and Cl are present in larger 3p orbital therefore interaction of F lone pair  electron with d-orbitals of silicon are stronger in F as compared Cl.b)Boron does not have d orbitals. Because of this, it is not possible for the element to expand on its octet. This, in turn, causes the maximum covalence of boron to be restricted to 4. Beyond this value, boron will become unstable and not be able to form $[BF_6]^{3-}$ ions.c)Nitric acid reacts with aluminium and forms a protective layer i.e. $Al_2O_3$. This protective layer makes aluminium unreactive towards $HNO_3$ and therefore, it can be stored in aluminium containers.