Chemistry GROUP-14 ELEMENTS

Topics to be covered

=> General introduction
=> Electronic configuration
=> Covalent radius
=> Ionization enthalpy
=> Electronegativity
=>Physical properties
=> Chemical properties

GROUP 14 ELEMENTS: THE CARBON FAMILY

color{green}(★) Carbon (color{red}(C)), silicon (color{red}(Si)), germanium (color{red}(Ge)), tin (color{red}(Sn)) and lead (color{red}(Pb)) are the members of group 14.

color{green}(★) Carbon is the seventeenth most abundant element by mass in the earth’s crust. It is widely distributed in nature in free as well as in the combined state.

color{green}(★) In elemental state it is available as coal, graphite and diamond; however, in combined state it is present as metal carbonates, hydrocarbons and carbon dioxide gas color{red}((0.03%)) in air.

color{green}(★) One can emphatically say that carbon is the most versatile element in the world. Its combination with other elements such as dihydrogen, dioxygen, chlorine and sulphur provides an astonishing array of materials ranging from living tissues to drugs and plastics.

color{green}(★) Organic chemistry is devoted to carbon containing compounds. It is an essential constituent of all living organisms.

color{green}(★) Naturally occurring carbon contains two stable isotopes :color{red}(text()^(12)C) and color{red}(text()^(13)C). In addition to these, third isotope, color{red}(text()^(14)C) is also present. It is a radioactive isotope with halflife color{red}(5770) years and used for radiocarbon dating.

color{green}(★) Silicon is the second (color{red}(27.7 %) by mass) most abundant element on the earth’s crust and is present in nature in the form of silica and silicates. Silicon is a very important component of ceramics, glass and cement.

color{green}(★) Germanium exists only in traces. Tin occurs mainly as cassiterite, color{red}(SnO_2) and lead as galena, color{red}(PbS).

color{green}(★) Ultrapure form of germanium and silicon are used to make transistors and semiconductor devices.

color{green}(★) The important atomic and physical properties of the group 14 elements along with their electronic configuration are given in Table 11.3 Some of the atomic, physical and chemical properties are discussed below :

Electronic Configuration

color{green}(★) The valence shell electronic configuration of these elements is color{red}(ns^2 np^2). The inner core of the electronic configuration of elements in this group also differs.

color{green}(★) There is a considerable increase in covalent radius from color{red}(C) to color{red}(Si), thereafter from color{red}(Si) to color{red}(Pb) a small increase in radius is observed. This is due to the presence of completely filled color{red}(d) and color{red}(f) orbitals in heavier members.

Ionization Enthalpy

color{green}(★) The first ionization enthalpy of group 14 members is higher than the corresponding members of group 13.

color{green}(★) The influence of inner core electrons is visible here also.

color{green}(★) In general the ionisation enthalpy decreases down the group.

color{green}(★) Small decrease in color{red}(Delta_iH) from color{red}(Si) to color{red}(Ge) to color{red}(Sn) and slight increase in color{red}(Delta_iH) from color{red}(Sn) to color{red}(Pb) is the consequence of poor shielding effect of intervening color{red}(d) and color{red}(f) orbitals and increase in size of the atom.

Electronegativity

color{green}(★) Due to small size, the elements of this group are slightly more electronegative than group 13 elements. The electronegativity values for elements from color{red}(Si) to color{red}(Pb) are almost the same.

Physical Properties

color{green}(★) All group 14 members are solids.

color{green}(★) Carbon and silicon are non-metals, germanium is a metalloid, whereas tin and lead are soft metals with low melting points.

color{green}(★) Melting points and boiling points of group 14 elements are much higher than those of corresponding elements of group 13.

Chemical Properties

color{green}("𝐎𝐱𝐢𝐝𝐚𝐭𝐢𝐨𝐧 𝐬𝐭𝐚𝐭𝐞𝐬 𝐚𝐧𝐝 𝐭𝐫𝐞𝐧𝐝𝐬 𝐢𝐧 𝐜𝐡𝐞𝐦𝐢𝐜𝐚𝐥 𝐫𝐞𝐚𝐜𝐭𝐢𝐯𝐢𝐭𝐲 :")

color{green}(★) The group 14 elements have four electrons in outermost shell.

color{green}(★) The common oxidation states exhibited by these elements are +4 and +2.

color{green}(★) Carbon also exhibits negative oxidation states.

color{green}(★) Since the sum of the first four ionization enthalpies is very high, compounds in +4 oxidation state are generally covalent in nature.

color{green}(★) In heavier members the tendency to show +2 oxidation state increases in the sequence color{red}(Ge < Sn < Pb). It is due to the inability of color{red}(ns^2) electrons of valence shell to participate in bonding. The relative stabilities of these two oxidation states vary down the group.

color{green}(★) Carbon and silicon mostly show +4 oxidation state. Germanium forms stable compounds in +4 state and only few compounds in +2 state. Tin forms compounds in both oxidation states (color{red}(Sn) in +2 state is a reducing agent).

color{green}(★) Lead compounds in +2 state are stable and in +4 state are strong oxidising agents.

color{green}(★) In tetravalent state the number of electrons around the central atom in a molecule (e.g., carbon in color{red}(C Cl_4)) is eight.

color{green}(★) Being electron precise molecules, they are normally not expected to act as electron acceptor or electron donor species. Although carbon cannot exceed its covalence more than 4, other elements of the group can do so. It is because of the presence of d orbital in them. Due to this, their halides undergo hydrolysis and have tendency to form complexes by accepting electron pairs from donor species. For example, the species like, color{red}(SiF_6^(2–)), color{red}([GeCl_6]^(2–)), color{red}([Sn(OH)_6]^(2–)) exist where the hybridisation of the central atom is color{red}(sp^3d^2).

color{green}("(𝐢) 𝐑𝐞𝐚𝐜𝐭𝐢𝐯𝐢𝐭𝐲 𝐭𝐨𝐰𝐚𝐫𝐝𝐬 𝐨𝐱𝐲𝐠𝐞𝐧 :")

color{brown}(★) All members when heated in oxygen form oxides.

color{brown}(★) There are mainly two types of oxides, i.e., monoxide and dioxide of formula color{red}(MO) and color{red}(MO_2) respectively.

color{brown}(★) color{red}(SiO) only exists at high temperature.

color{brown}(★) Oxides in higher oxidation states of elements are generally more acidic than those in lower oxidation states.

color{brown}(★) The dioxides color{red}(— CO_2, SiO_2) and color{red}(GeO_2) are acidic, whereas color{red}(SnO_2) and color{red}(PbO_2) are amphoteric in nature.

color{brown}(★) Among monoxides, color{red}(CO) is neutral, color{red}(GeO) is distinctly acidic whereas color{red}(SnO) and color{red}(PbO) are amphoteric.

color{green}("(𝐢𝐢) 𝐑𝐞𝐚𝐜𝐭𝐢𝐯𝐢𝐭𝐲 𝐭𝐨𝐰𝐚𝐫𝐝𝐬 𝐰𝐚𝐭𝐞𝐫 : ")

color{brown}(★) Carbon, silicon and germanium are not affected by water.

color{brown}(★) Tin decomposes steam to form dioxide and dihydrogen gas.

color{red}(Sn + 2H_2O overset(Delta)→ SnO_2+2H_2)

color{brown}(★) Lead is unaffected by water, probably because of a protective oxide film formation.

color{green}("(𝐢𝐢𝐢) 𝐑𝐞𝐚𝐜𝐭𝐢𝐯𝐢𝐭𝐲 𝐭𝐨𝐰𝐚𝐫𝐝𝐬 𝐡𝐚𝐥𝐨𝐠𝐞𝐧: ")

color{brown}(★) These elements can form halides of formula color{red}(MX_2) and color{red}(MX_4) (where color{red}(X = F, Cl, Br, I) ).

color{brown}(★) Except carbon, all other members react directly with halogen under suitable condition to make halides. Most of the color{red}(MX_4) are covalent in nature. The central metal atom in these halides undergoes color{red}(sp^3) hybridisation and the molecule is tetrahedral in shape. Exceptions are color{red}(SnF_4) and color{red}(PbF_4), which are ionic in nature. color{red}(PbI_4) does not exist because color{red}(Pb)—I bond initially formed during the reaction does not release enough energy to unpair color{red}(6s^2) electrons and excite one of them to higher orbital to have four unpaired electrons around lead atom. Heavier members color{red}(Ge) to color{red}(Pb) are able to make halides of formula color{red}(MX_2). Stability of dihalides increases down the group. Considering the thermal and chemical stability, color{red}(GeX_4) is more stable than color{red}(GeX_2), whereas color{red}(PbX_2) is more than color{red}(PbX_4). Except color{red}(C Cl_4), other tetrachlorides are easily hydrolysed by water because the central atom can accommodate the lone pair of electrons from oxygen atom of water molecule in d orbital.

color{brown}(★) Hydrolysis can be understood by taking the example of color{red}(SiCl_4). It undergoes hydrolysis by initially accepting lone pair of electrons from water molecule in color{red}(d) orbitals of color{red}(Si), finally leading to the formation of color{red}(Si(OH)_4) as shown below :

Q 3245212163

Select the member(s) of group 14 that (i) forms the most acidic dioxide, (ii) is commonly found in +2 oxidation state, (iii) used as semiconductor.

Solution:

(i) carbon

[SiF_6]^(2-) is known whereas [SiCl_6]^(2-) not.Give possible reasons.
(i) six large chloride ions cannot be accommodated around Si^(4+) due to limitation of its size.
(ii) interaction between lone pair of chloride ion and Si^(4+) is not very strong.