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Chemistry Case study (4 Marks)

The p-Block Elements · Gujarat Board (GSEB) STD 11 Science (GSEB - English Medium). 5 questions.

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Case study (4 Marks)

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Question 14 Marks
Read the passage given below and answer the following questions from $1$ to $5$.
It is prepared by complete combustion of Carbon and carbon containing fuels in excess Of air.
$\text{C(s)}+\text{O}_2\text{(g)}\xrightarrow{\triangle}\text{CO}_2\text{(g)}$
$\text{CH}_4\text{(g)}+2\text{O}_2\text{(g)}\rightarrow\text{CO}_2\text{(g)}+2\text{H}_2\text{O}\text{(g)}$
In the laboratory it is conveniently Prepared by the action of dilute HCl on calcium Carbonate.
$CaCO_3 (s) + 2HCl (aq) \rightarrow CaCl_2 (aq) + CO_2(g) + H_2O(l)$
$\text{H}_2\text{CO}_3(\text{aq})+\text{H}_2\text{O}\text{(l)}\rightleftharpoons\text{HCO}_3^-\text{(aq)}+\text{H}_3\text{O}^+\text{(aq)}$
$\text{H}\text{CO}_3^-(\text{aq})+\text{H}_2\text{O}\text{(l)}\rightleftharpoons\text{CO}_3^{2-}\text{(aq)}+\text{H}_3\text{O}^+\text{(aq)}$
Buffer system helps to Maintain pH of blood between $7.26$ to $7.42$. Being acidic in nature, it combines with alkalies To form metal carbonates. Carbon dioxide, which is normally present To the extent of $\sim0.03 %$ by volume in the Atmosphere, is removed from it by the process Known as photosynthesis. It is the process By which green plants convert atmospheric $CO_2$ into carbohydrates such as glucose. The Overall chemical change can be expressed as:
$6\text{CO}_2+12\text{H}_2\text{O}\xrightarrow[\text{Chlorophyll}]{\text{hv}}\text{C}_6\text{H}_{12}\text{O}_6+6\text{O}_2$
By this process plants make food for Themselves as well as for animals and human Beings. Unlike $CO$, it is not poisonous. But the Increase in combustion of fossil fuels and Decomposition of limestone for cement Manufacture in recent years seem to increase The $CO_2$ content of the atmosphere. This may Lead to increase in green house effect and Thus, raise the temperature of the atmosphere Which might have serious consequences. Carbon dioxide can be obtained as a solid In the form of dry ice by allowing the liquified $CO_2$ to expand rapidly. Dry ice is used as a Refrigerant for ice-cream and frozen food. Gaseous $CO_2$ is extensively used to carbonate Soft drinks. Being heavy and non-supporter Of combustion it is used as fire extinguisher. A Substantial amount of $CO_2$ is used to Manufacture urea. In $CO_2$ molecule carbon atom undergoes Sp hybridisation. Two sp hybridised orbitals Of carbon atom overlap with two p orbitals of Oxygen atoms to make two sigma bonds while Other two electrons of carbon atom are involved.

In $\text{p}\pi-\text{p}\pi$ bonding with oxyglargeen atom. This Results in its linear shape $[$with both $C–O$ bonds Of equal length $(115 pm)]$ with no dipole Moment. The resonance structures are shown Below: Resonance structures of carbon dioxide.
Silicon Dioxide, $SiO_2 95 \%$ of the earth’s crust is made up of silica And silicates. Silicon dioxide, commonly known As silica, occurs in several crystallographic Forms. Quartz, cristobalite and tridymite are Some of the crystalline forms of silica, and they Are interconvertable at suitable temperature. Silicon dioxide is a covalent, three-dimensional network solid in which each silicon atom is Covalently bonded in a tetrahedral manner to Four oxygen atoms. Each oxygen atom in turn Covalently bonded to another silicon atoms as Shown in diagram. Each corner is Shared with another tetrahedron. The entire Crystal may be considered as giant molecule In which eight membered rings are formed with Alternate silicon and oxygen atoms. Silica in its normal form is almost non- Reactive because of very high $Si—O$ bond Enthalpy. It resists the attack by halogens, Dihydrogen and most of the acids and metals Even at elevated temperatures. However, it is Attacked by HF and NaOH.
$SiO_2 + 2NaOH \rightarrow Na2SiO_3 + H_2O SiO_2 + 4HF \rightarrow SiF_4 + 2H_2O$
Quartz is extensively used as a piezoelectric Material; it has made possible to develop extremely Accurate clocks, modern radio and television Broadcasting and mobile radio communications. Silica gel is used as a drying agent and as a support For chromatographic materials and catalysts. Kieselghur, an amorphous form of silica is used In filtration plants.
Silicones are a group of organosilicon polymers, Which have $(R_2SiO)$ as a repeating unit. The Starting materials for the manufacture of Silicones are alkyl or aryl substituted silicon Chlorides, RnSiCl(4–n), where R is alkyl or aryl Group. When methyl chloride reacts with Silicon in the presence of copper as a catalyst At a temperature $573K$ various types of methyl substituted chlorosilane of formula $MeSiCl_3, Me_2SiCl_2, Me3SiCl$ with small amount of $Me4Si$ Are formed. Hydrolysis of dimethyl- Dichlorosilane, $(CH_3) 2SiCl_2$ followed by Condensation polymerisation yields straight Chain polymers.
A large number of silicates minerals exist in Nature. Some of the examples are feldspar, Zeolites, mica and asbestos. The basic structural unit of silicates is $SiO_4^{4–}$ In which silicon atom is bonded to four Oxygen atoms in tetrahedron fashion. In Silicates either the discrete unit is present or A number of such units are joined together Via corners by sharing $1, 2, 3$ or $4$ oxygen Atoms per silicate units. When silicate units Are linked together, they form chain, ring, Sheet or three-dimensional structures. Negative charge on silicate structure is Neutralised by positively charged metal ions. If all the four corners are shared with other Tetrahedral units, three-dimensional network Is formed. Two important man-made silicates are Glass and cement. Zeolites If aluminium atoms replace few silicon atoms In three-dimensional network of silicon dioxide, Overall structure known as aluminosilicate, Acquires a negative charge. Cations such as $Na+, K+$ Or $Ca_2+$ balance the negative charge. Examples are feldspar and zeolites.
Zeolites are Widely used as a catalyst in petrochemical Industries for cracking of hydrocarbons and Isomerisation, e.g., $ZSM-5$ (A type of zeolite) Used to convert alcohols directly into gasoline. Hydrated zeolites are used as ion exchangers In softening of “hard” water.
  1. … is used as a Refrigerant for ice-cream and frozen food.
  1. Dry ice
  2. Wet ice
  3. Crescent Ice
  4. Nugget Ice
  1. $H_2CO_3$ is a …
  1. strong dibasic acid
  2. weak dibasic acid
  3. weak diacidic base
  4. Strong diacidic base
  1. … is extensively used as a piezoelectric Material.
  1. Glass
  2. Ferrite
  3. Quartz
  4. Saphire
  1. … an amorphous form of silica is used In filtration plants.
  1. Ferrite
  2. Quartz
  3. Saphire
  4. Kieselghur
  1. Which of the following is not an example of silicate mineral ?
  1. feldspar
  2. mica
  3. asbestos
  4. hematite
Answer
  1. (a) Dry ice
  2. (b) weak dibasic acid
  3. (c) Quartz
  4. (d) Kieselghur
  5. (d) hematite
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Question 24 Marks
Read the passage given below and answer the following questions from 1 to 5.
Oxidation state and trends in chemical Reactivity Due to small size of boron, the sum of its first Three ionization enthalpies is very high. This Prevents it to form +3 ions and forces it to form Only covalent compounds. But as we move from B to Al, the sum of the first three ionisation Enthalpies of Al considerably decreases, and Is therefore able to form $Al^{3+}$ ions. In fact, Aluminium is a highly electropositive metal. However, down the group, due to poor Shielding effect of intervening d and f orbitals, The increased effective nuclear charge holds ns Electrons tightly (responsible for inert pair Effect) and thereby, restricting their Participation in bonding. As a result of this, Only p-orbital electron may be involved in Bonding. In fact in Ga, In and Tl, both +1 and +3 oxidation states are observed. The relative Stability of +1 oxidation state progressively Increases for heavier elements: A l< Ga < In< Tl. In Thallium +1 oxidation state is predominant whereas the +3 oxidation state is highly Oxidising in character. The compounds in +1 oxidation state, as expected from energy Considerations, are more ionic than those in +3 oxidation state.
Important trends and anomalous properties of boron – certain important trends can be observed in the chemical behaviour of group 13 elements. The tri-chlorides, bromides and iodides of all these elements being covalent in nature are hydrolysed in water. Species like tetrahedral $[M(OH)_4]^–$ and octahedral $[M(H_2O)6]^{3+}$, except in boron, exist in aqueous medium. The monomeric trihalides, being electron deficient, are strong Lewis acids. Boron trifluoride easily reacts with Lewis bases such as $NH_3$ to complete octet around boron. It is due to the absence of d orbitals that the maximum covalence of B is 4. Since the d orbitals are available with Al and other elements, the maximum covalence can be expected beyond 4. Most of the other metal halides (e.g., $AlCl_3$) are dimerised through halogen bridging (e.g., $Al2Cl_6$). The metal species completes its octet by accepting electrons from halogen in these halogen bridged molecules.
i) Reactivity towards air Boron is unreactive in crystalline form. Aluminium forms a very thin oxide layer on The surface which protects the metal from Further attack. Amorphous boron and Aluminium metal on heating in air form $B_2O_3$ And $Al_2O_3$ respectively. With dinitrogen at high Temperature they form nitrides. The nature of these oxides varies down the Group. Boron trioxide is acidic and reacts with Basic (metallic) oxides forming metal borates. Aluminium and gallium oxides are amphoteric And those of indium and thallium are basic in Their properties.
ii) Reactivity towards acids and alkalies Boron does not react with acids and alkalies Even at moderate temperature; but aluminium Dissolves in mineral acids and aqueous alkalies And thus shows amphoteric character. Aluminium dissolves in dilute HCl and Liberates dihydrogen.
$2Al(s) + 6HCl (aq) \rightarrow 2Al_3^+ (aq) + 6Cl^– (aq) + 3H_2 (g)$
However, concentrated nitric acid renders Aluminium passive by forming a protective Oxide layer on the surface. Aluminium also reacts with aqueous alkali And liberates dihydrogen.
$2Al (s) + 2NaOH(aq) + 6H_2O(l) \rightarrow 2 Na+ [Al(OH)_4]^– (aq) + 3H_2(g)$
Sodium Tetrahydroxoaluminate(III).
iii) Reactivity towards halogens These elements react with halogens to form Trihalides (except TlI3). $2E(s) + 3 X_2 (g) \rightarrow 2EX_3 (s) (X = F, Cl, Br, I)$
Borax- It is the most important compound of boron. It is a white crystalline solid of formula $Na_2B_4O_7⋅10H_2O$. In fact it contains the Tetranuclear units and correct Formula; therefore, is $Na2 [B4O5 (OH) 4].8H2O$. Borax dissolves in water to give an alkaline Solution.
$Na_2B_4O7 + 7H_2O \rightarrow 2NaOH + 4H_3BO_3$
On heating, borax first loses water Molecules and swells up. On further heating it Turns into a transparent liquid, which solidifies Into glass like material known as borax Bead. $Na_2B_4O_7.10H_2O \rightarrow Na^2B_4O_7\rightarrow 2NaBO_2+ B2O_3​​​​​​​$
Metaborate Boric Anhydride The metaborates of many transition metals Have characteristic colours and, therefore, Borax bead test can be used to identify them In the laboratory. For example, when borax is Heated in a Bunsen burner flame with CoO on A loop of platinum wire, a blue coloured Co(BO2) 2 bead is formed.
Orthoboric acid, $H_3BO_3$ is a white crystalline Solid, with soapy touch. It is sparingly soluble In water but highly soluble in hot water. It can Be prepared by acidifying an aqueous solution Of borax.
$Na_2B_4O_7 + 2HCl + 5H_2O \rightarrow 2NaCl + 4B(OH)_3​​​​​​​$
It is also formed by the hydrolysis (reaction With water or dilute acid) of most boron Compounds (halides, hydrides, etc.). It has a layer structure in which planar $BO_3$ units are Joined by hydrogen.
  1. Boron is … in crystalline form.
  1. unreactive
  2. highly reactive
  3. less reactive
  4. only (a) or (c)
  1. Orthoboric acid is …
  1. Amorphous
  2. Crystalline
  3. Polyamorphous
  4. None of above
  1. Aluminium and gallium oxides are … in their properties.
  1. acidic
  2. Basic
  3. amphoteric
  4. None of above
  1. Indium and thallium are … in their properties.
  1. acidic
  2. Alkali
  3. amphoteric
  4. basic
  1. Aluminium is a highly … metal.
  1. electronegative
  2. Neutral
  3. electropositive
  4. None of above
Answer
  1. (a) unreactive
  2. (b) crystalline
  3. (c) amphoteric
  4. (d) basic
  5. (c) electropositive
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Question 34 Marks
Read the passage given below and answer the following questions from 1 to 5 .
Carbon exhibits many allotropic forms; both crystalline as well as amorphous. Diamond and graphite are two wellknown crystalline forms of carbon. In 1985, third form of carbon known as fullerenes was discovered by H.W.Kroto, E.Smalley and R.F.Curl. For this discovery they were awarded the Nobel Prize in 1996.
Diamond It has a crystalline lattice. In diamond each carbon atom undergoes $sp ^3$ hybridisation and linked to four other carbon atoms by using hybridised orbitals in tetrahedral fashion. The C-C bond length is 154 pm . The structure extends in space and produces a rigid three- dimensional network of carbon atoms. It is very difficult to break extended covalent bonding and, therefore, diamond is a hardest substance on the earth. It is used as an abrasive for sharpening hard tools, in making dyes and in the manufacture of tungsten filaments for electric light bulbs. Graphite Graphite has layered structure. Layers are held by van der Waals forces and distance between two layers is 340 pm . Each layer is composed of planar hexagonal rings of carbon atoms. C-C bond length within the layer is 141.5 pm . Each carbon atom in hexagonal ring undergoes $sp ^2$ hybridisation and makes three sigma bonds with three neighbouring carbon atoms. Fourth electron forms a $\pi$ bond. The electrons are delocalised over the whole sheet. Electrons are mobile and, therefore, graphite conducts electricity along the sheet. Graphite cleaves easily between the layers and, therefore, it is very soft and slippery. For this reason graphite is used as a dry lubricant in machines running at high temperature, where oil cannot be used as a lubricant.
Fullerenes Fullerenes are made by the heating of graphite in an electric arc in the presence of inert gases such as helium or argon. The sooty material formed by condensation of vapourised Cn small molecules consists of mainly C60 with smaller quantity of C70 and traces of fullerenes consisting of even number of carbon atoms up to 350 or above. Fullerenes are the only pure form of carbon because they have smooth structure without having 'dangling' bonds. Fullerenes are cage like molecules. C60 molecule has a shape like soccer ball and called Buckminsterfullerene. It contains twenty six-membered rings and twelve five-membered rings. A six membered ring is fused with six or five membered rings but a five membered ring can only fuse with six membered rings. All the carbon atoms are equal and they undergo $sp ^2$ hybridisation. Each carbon atom forms three sigma bonds with other three carbon atoms. The remaining electron at each carbon is delocalised in molecular orbitals, which in turn give aromatic character to molecule. This ball shaped molecule has 60 vertices and each one is occupied by one carbon atom and it also contains both single and double bonds with C-C distances of 143.5 pm and 138.3 pm respectively. Spherical fullerenes are also called bucky balls in short.
Uses of Carbon Graphite fibres embedded in plastic material form high strength, lightweight composites. The composites are used in products such as tennis rackets, fishing rods, aircrafts and canoes. Being good conductor, graphite is used for electrodes in batteries and industrial electrolysis. Crucibles made from graphite are inert to dilute acids and alkalies. Being highly porous, activated charcoal is used in adsorbing poisonous gases; also used in wateof filters to remove organic contaminators and in airconditioning system to control odour. Carbon black is used as black pigment in black ink and as filler in automobile tyres. Coke is used as a fuel and largely as a reducing agent in metallurgy. Diamond is a precious stone and used in jewellery. It is measured in carats (1 carat = 200 mg ). Carbon Monoxide Direct oxidation of C in limited supply of oxygen or air yields carbon monoxide. $2 C ( s ) O ( g ) \rightarrow$ $2 CO ( g )$

When air is used instead of steam, a mixture of CO and $N_2$ is produced, which is called producer gas.
Water gas and producer gas are very important industrial fuels. Carbon monoxide in water gas or producer gas can undergo further combustion forming carbon dioxide with the liberation of heat. Carbon monoxide is a colourless, odourless and almost water insoluble gas. It is a powerful reducing agent and reduces almost all metal oxides other than those of the alkali and alkaline earth metals, aluminium and a few transition metals. This property of CO is used in the extraction of many metals from their oxides ores.
$\text{Fe}_2\text{O}_3(\text{s})+3\text{CO}(\text{g})\xrightarrow{\triangle}2\text{Fe}(\text{s})+3\text{CO}_2\text{(g)}$
$\text{ZnO}\text{(s)}+\text{CO}\text{(s)}\xrightarrow{\triangle}\text{Zn}(\text{s})+\text{CO}_2(\text{g})$
In CO molecule, there are one sigma and two π bonds between carbon and oxygen: C ≡ O Because of the presence of a lone pair on carbon, CO molecule acts as a donor and reacts with certain metals when heated to form metal carbonyls. The highly poisonous nature of CO arises because of its ability to form a complex with haemoglobin, which is about 300 times more stable than the oxygen-haemoglobin complex. This prevents haemoglobin in the red blood corpuscles from carrying oxygen round the body and ultimately resulting in death.
  1. In diamond each carbon atom undergoes … hybridisation.
  1. sp
  2. $sp^2$
  3. $sp^3$
  4. $sp^3d$
  1. Carbon atom in hexagonal ring undergoes … hybridisation.
  1. $sp$
  2. $sp^2$
  3. $sp^3$
  4. $sp^3d$
  1. C—C bond length within the layer in graphite is … pm.
  1. 5
  2. 5
  3. 180
  4. 90
  1. Fullerenes was discovered by …
  1. W.Kroto
  2. Smalley
  3. F.Curl
  4. All the above
  1. The C–C bond length in diamond is … pm.
  1. 5
  2. 5
  3. 180
  4. 154
Answer
  1. (c)$ sp^3$
  2. (b) $sp^2$
  3. (b)$141.5$
  4. (d) All the above
  5. (d) $154$
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Question 44 Marks
Read the passage given below and answer the following questions from 1 to 5 .
Group 14 elements: the carbon family-Carbon, silicon, germanium, tin lead and Flerovium are the members of group 14. 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. 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 ( $0.03 \%$ ) in air. 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.
The valence shell electronic configuration of These elements is $ns ^2 np ^2$. The inner core of the Electronic configuration of elements in this Group also differs.
Covalent Radius There is a considerable increase in covalent Radius from C to Si, thereafter from Si to Pb a Small increase in radius is observed. This is Due to the presence of completely filled d and f Orbitals in heavier members. Ionization Enthalpy The first ionization enthalpy of group 14 Members is higher than the corresponding Members of group 13. The influence of inner Core electrons is visible here also. In general the lonisation enthalpy decreases down the group. Small decrease in $\Delta iH$ from Si to Ge to Sn and Slight increase in $\Delta i H$ from Sn to Pb is the Consequence of poor shielding effect of Intervening $d$ and $f$ orbitals and increase in size Of the atom. Electronegativity Due to small size, the elements of this group Are slightly more electronegative than group 13 elements. The electronegativity values for Elements from Si to Pb are almost the same.
Physical Properties All members of group14 are solids. Carbon and Silicon are non-metals, germanium is a metalloid, Whereas tin and lead are soft metals with low Melting points. Melting points and boiling points Of group 14 elements are much higher than those Of corresponding elements of group 13.
(i) Reactivity towards oxygen All members when heated in oxygen form Oxides. There are mainly two types of oxides, i.e., monoxide and dioxide of formula MO and $MO _2$ respectively. SiO only exists at high Temperature. Oxides in higher oxidation states Of elements are generally more acidic than Those in lower oxidation states. The dioxides $CO _2$, SiO 2 and $GeO _2$ are acidic, whereas $SnO _2$ and $PbO _2$ are amphoteric in nature. Among monoxides, CO is neutral, GeO is Distinctly acidic whereas SnO and PbO are Amphoteric.
(ii) Reactivity towards water Carbon, silicon and germanium are not Affected by water. Tin decomposes steam to Form dioxide and dihydrogen gas.
$Sn+2 H_2 O \rightarrow SnO_2+2 H_2$
Lead is unaffected by water, probably Because of a protective oxide film formation.
(iii) Reactivity towards halogen These elements can form halides of formula $M X_2$ and $M X_4$ (where $\left.X=F, C l, B r, I\right)$. Except Carbon, all other members react directly with Halogen under suitable condition to make Halides. Most of the $MX _4$ are covalent in nature. The central metal atom in these halides Undergoes $sp ^3$ hybridisation and the molecule Is tetrahedral in shape. Exceptions are $SnF _4$ And $PbF _4$, which are ionic in nature.
Carbon atoms have the tendency to link With one another through covalent bonds to Form chains and rings. This property is called Catenation. This is because C-C bonds are Very strong. Down the group the size increases and electronegativity decreases, and, thereby, Tendency to show catenation decreases. This Can be clearly seen from bond enthalpies Values. The order of catenation is $C > Si > Ge \approx Sn$. Lead does not show catenation.
  1. Which of the following is not the member of group 14 ?
  1. boron
  2. silicon
  3. germanium
  4. tin
  1. … does not show catenation.
  1. Carbon
  2. Lead
  3. Silicon
  4. Germanium
  1. Which of following elements are affected by water ?
  1. carbon
  2. silicon
  3. germanium
  4. All the above
  1. The valence shell electronic configuration of Group 14 elements is …
  1. $ns^2np^4$
  2. $ns^2np^5$
  3. $ns^2np^2$
  4. $ns^2np^3$
  1. Half-life of $^{14}C$ is … years.
  1. 6570
  2. 4570
  3. 5770
  4. 1970
Answer
  1. (a) boron
  2. (b) Lead
  3. (d) All the above
  4. (c) $ns^2np^2$​​​​​​​
  5. (c) 5770
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Question 54 Marks
Read the passage given below and answer the following questions from 1 to 5 .
In p-block elements the last electron enters the outermost p orbital. As we know that the number of p orbitals is three and, therefore, the maximum number of electrons that can be accommodated in a set of p orbitals is six. Consequently there are six groups of p-block elements in the periodic table numbering from 13 to 18 . Boron, carbon, nitrogen, oxygen, fluorine and helium head the groups. Their valence shell electronic configuration is $ns ^2 np ^{1-}$ ${ }^6$ (except for He). The inner core of the electronic configuration may, however, differ. The difference in inner core of elements greatly influences their physical properties (such as atomic and ionic radii, ionisation enthalpy, etc.) as well as chemical properties. The occurrence of oxidation states two unit less than the group oxidation states are sometime attributed to the 'inert pair effect'.
Group 13 elements: the boron family This group elements show a wide variation in properties. Boron is a typical non-metal, aluminium is a metal but shows many chemical similarities to boron, and gallium, indium, thallium and nihonium are almost exclusively metallic in character. Boron is a fairly rare element, mainly occurs as orthoboric acid, $\left( H _3 BO _3\right)$, borax, $Na _2 B_4 O _7 \cdot 10 H _2 O$, and kernite, $Na _2 B_4 O _7 \cdot 4 H _2 O$. In India borax occurs in Puga Valley (Ladakh) and Sambhar Lake (Rajasthan). The abundance of boron in earth crust is less than $0.0001 \%$ by mass. There are two isotopic forms of boron $10 B(19 \%)$ and $11 B(81 \%)$. Aluminium is the most abundant metal and the third most abundant element in the earth's crust ( $8.3 \%$ by mass) after oxygen ( $45.5 \%$ ) and $Si (27.7 \%)$. Bauxite, $Al 2 O 3.2 H _2 O$ and cryolite, Na3AIF6 are the important minerals of aluminium. In India it is found as mica in Madhya Pradesh, Karnataka, Orissa and Jammu. Gallium, indium and thallium are less abundant elements in nature. Nihonium has symbol Nh, atomic number 113 , atomic mass $286 g mol ^{-1}$ and electronic configuration $[R n] 5 f^{14} 6 d^{10} 7 s^2 7 p ^2$. So far it has been prepared in small amount and half life of its most stable isotope is 20 seconds. Due to these reasons its chemistry has not been established. Nihonium is a synthetically prepared radioactive element. Here atomic, physical and chemical properties of elements of this group leaving nihonium are discussed below.
The outer electronic configuration of these elements is $n s 2 n{ }^1$. A close look at the electronic configuration suggests that while boron and aluminium have noble gas core, gallium and indium have noble gas plus 10 d electrons, and thallium has noble gas plus 14 f - electrons plus 10 d -electron cores. Thus, the electronic structures of these elements are more complex than for the first two groups of elements discussed in unit 10. This difference in electronic structures affects the other properties and consequently the chemistry of all the elements of this group. Atomic Radii On moving down the group, for each successive member one extra shell of electrons is added and, therefore, atomic radius is expected to increase. However, a deviation can be seen. Atomic radius of Ga is less than that of Al. This can be understood from the variation in the inner core of the electronic configuration. The presence of additional 10 d -electrons offer only poor screening effect (Unit 2) for the outer electrons from the increased nuclear charge in gallium. Consequently, the atomic radius of gallium ( 135 pm ) is less than that of aluminium (143 pm ).
Boron is non-metallic in nature. It is extremely hard and black coloured solid. It exists in many allotropic forms. Due to very strong crystalline lattice, boron has unusually high melting point. Rest of the members are soft metals with low melting point and high electrical conductivity. It is worthwhile to note that gallium with unusually low melting point ( 303 K ), could exist in liquid state during summer. Its high boiling point ( 2676 K ) makes it a useful material for measuring high temperatures. Density of the elements increases down the group from boron to thallium.
  1. There are … groups of p–block elements in the periodic table.
  1. six
  2. seven
  3. eight
  4. two
  1. Boron is … in nature.
  1. metallic
  2. non-metallic
  3. metalloid
  4. All the above
  1. Boiling point of gallium is …
  1. 303K
  2. 1345K
  3. 2676 K
  4. 1854K
  1. The occurrence of oxidation states two unit less than the group oxidation states are sometime attributed to the …
  1. loan pair effect
  2. middle pair effect
  3. outer pair effect
  4. inert pair effect
  1. Density of the elements … down the group from boron to thallium.
  1. increases
  2. decreases
  3. remains constant
  4. none of above
Answer
  1. (a) six
  2. (b) non-metallic
  3. (c) 2676 K
  4. (d) inert pair effect
  5. (a) increases
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