CLASS
XI
CBSE-i
UNIT-12
CHEMISTRY
Some p-Block Elements TEACHERS’ MANUAL
Shiksha Kendra, 2, Community Centre, Preet Vihar, Delhi-110 092 India
CBSE-i CHEMISTRY
Some p-Block Elements TEACHERS’ MANUAL
CLASS
XI
UNIT-12
Shiksha Kendra, 2, Community Centre, Preet Vihar, Delhi-110 092 India
The CBSE-International is grateful for permission to reproduce and/or translate copyright material used in this publication. The acknowledgements have been included wherever appropriate and sources from where the material may be taken are duly mentioned. In case any thing has been missed out, the Board will be pleased to rectify the error at the earliest possible opportunity. All Rights of these documents are reserved. No part of this publication may be reproduced, printed or transmitted in any form without the prior permission of the CBSE-i. This material is meant for the use of schools who are a part of the CBSE-International only.
Preface Education plays the most important role in acquiring professional and social skills and a positive attitude to face the challenges of life. Curriculum is a comprehensive plan of any educational programme. It is also one of the means of bringing about qualitative improvement in an educational system. The Curriculum initiated by Central Board of Secondary Education -International (CBSE-i) is a progressive step in making the educational content responsive to global needs. It signifies the emergence of a fresh thought process in imparting a curriculum which would restore the independence of the learner to pursue the learning process in harmony with the existing personal, social and cultural ethos. The CBSE introduced the CBSE-i curriculum as a pilot project in few schools situated outside India in 2010 in classes I and IX and extended the programme to classes II, VI and X in the session 2011-12. It is going to be introduced in classes III, VII and for Senior Secondary classes with class XI in the session 2012-13. The Senior Secondary stage of education decides the course of life of any student. At this stage it becomes extremely important for students to develop the right attitude, a willingness to learn and an understanding of the world around them to be able to take right decisions for their future. The senior secondary curriculum is expected to provide necessary base for the growth of knowledge and skills and thereby enhance a student's potential to face the challenges of global competitiveness. The CBSE-i Senior Secondary Curriculum aims at developing desired professional, managerial and communication skills as per the requirement of the world of work. CBSE-i is for the current session offering curriculum in ten subjects i.e. Physics Chemistry, Biology, Accountancy, Business-Studies, Economics, Geography, ICT, English, Mathematics I and Mathematics II. Mathematics at two levels caters to the differing needs of students of pure sciences or commerce. The Curriculum has been designed to nurture multiple intelligences like linguistic or verbal intelligence, logicalmathematical intelligence, spatial intelligence, sports intelligence, musical intelligence, inter-personal intelligence and intra-personal intelligence. The Core skills are the most significant aspects of a learner's holistic growth and learning curve. The objective of this part of the core of curriculum is to scaffold the learning experiences and to relate tacit knowledge with formal knowledge. This involves trans-disciplinary linkages that would form the core of the learning process. Perspectives, SEWA (Social Empowerment through Work and Action), Life Skills and Research would be the constituents of this 'Core'. The CBSE-i Curriculum evolves by building on learning experiences inside the classroom over a period of time. The Board while addressing the issues of empowerment with the help of the schools' administering this system strongly recommends that practicing teachers become skilful and lifelong learners and also transfer their learning experiences to their peers through the interactive platforms provided by the Board. The success of this curriculum depends upon its effective implementation and it is expected that the teachers will make efforts to create better facilities, develop linkages with the world of work and foster conducive environment as per recommendations made in the curriculum document. I appreciate the effort of Dr.Sadhana Parashar, Director (Training), CBSE, Dr. Srijata Das, Education Officer, CBSE and Ms. Anjali Chhabra, Assistant Education Officer, CBSE and their teams involved in the development of this document. The CBSE-i website enables all stakeholders to participate in this initiative through the discussion forums. Any further suggestions on improving the portal are always welcome. Vineet Joshi Chairman, CBSE
Acknowledgements Advisory Shri Vineet Joshi, Chairman, CBSE Dr. Sadhana Parashar, Director (Training), CBSE Ideators Classes XI and XII Prof. A K Bakshi Dr. N K Sehgal Prof. Kapil Kapor Ms. Renu Anand Dr. Barkatullah Khan Ms. Avnita Bir
Conceptual Framework Shri G. Balasubramanian, Former Director (Acad), CBSE Ms. Abha Adams, Consultant, Step-by-Step School, Noida Dr. Sadhana Parashar, Director (Training), CBSE
Ms. P Rajeshwari Ms. Gyatri Khanna Mrs. Anita Makkar Prof. Biswajit Nag Ms. Usha Sharma
Dr. Niti Nandini Chatnani Dr. Anil K Bali Dr. Preeti Tewai Dr. Deeksha Bajpai Mr. S K Agarwala
Ms. Neeta Rastogi Dr. Anshu Dr. Rajesh Hassija Mr. Mukesh Kumar Dr. Om Vikas
Material Production Groups: Classes XI-XII English : Ms. Gayatri Khanna Ms. Renu Anand Ms. P Rajeshwary Ms. Sandhya Awasthi Ms. Manna Barua Ms. Veena Bhasin Ms. Urmil Guliani Ms. Sudha Ravi Mr. Anil Kumar Ms. Vijaylaxmi Raman Ms. Neerada Suresh Ms. Himaal Handoo Chemistry : Dr. G S Sodhi Dr. Vimal Rarh Dr. Shalini Baxi Dr. Vinita Arora Dr. Vandana Soni Ms. Charu Maini Ms. Rashmi Sharma Ms. Kavita Kapoor
Biology : Dr. Ranjana Saxena Dr. Neeraja Sood Dr. P Chitralekha Ms. Mridula Arora Ms. Lucy Jad Ms. Priyanka Choudhury Ms. Prerna Gosain Ms. Malini Sridhar
Geography: Dr. Preeti Tewari Ms. Rupa Das Mr. S Fazal Daoud Firdausi Ms. Neena Phogat Ms. Sujata Sharma Ms. Deepa Kapoor Ms. Bharti Malhotra Ms. Isha Kaushik Mr. Riyaz Khan
Physics : Dr. B. Biswal Ms. Namarata Alwadhi Mr. Dhirender Sharma Ms. Vandana Banga Mr. Vivek
Economics: Mr. S K Agarwala Ms. Ambika Gulati Ms. Nidhi Singh Ms. Malti Modi Ms. Sapna Das Ms. Ingur Agarwal Ms. Shankar Kulkarni Mr. Sandeep Sethi
Mathematics : Dr. Sushil Kumar Mrs. Monica Talwar Mrs. Charu Dureja Mrs. Seema Juneja Dr. H L Bhatia Dr. Sushma Bansal Mrs. Neeru Aggarwal Dr. Saroj Khanna
Accountancy : Mr. S S Sehrawat Dr. K Mohna Dr. Balbir Singh Ms. Bhupendra Kriplani Ms. Shipra Vaidya Mr. Sandeep Sethi Business Studies : Dr. S K Bhatia Ms. Meenu Ranjan Arora Mrs. Shegorika Mr. Sandeep Sethi Ms. Usha Sharma Ms. Komal Bhatia Ms. Ravisha Aggarwal ICT : Mr. Mukesh Kumar Ms. Nancy Sehgal Ms. Purvi Srivastava Ms. Gurpreet Kaur
Coordinators: Ms. Sugandh Sharma, EO
Dr Rashmi Sethi, EO
Ms. S. Radha Mahalakshmi, EO Mr. Navin Maini, RO (Tech)
Ms. Madhuchhanda, RO (Inn) Shri Al Hilal Ahmed, AEO
Ms. Anjali Chhabra, AEO
Shr. R. P. Singh, AEO
Shri R. P. Sharma, Consultant (Science)
Ms. Reema Arora, Consultant (Chemistry)
Mr. Sanjay Sachdeva, SO
Ms. Neelima Sharma, Consultant (English)
Contents Preface Acknowledgement Syllabus Coverage
1
Learning Outcomes
2
Lesson Plan Matrix
3
Cross-curricular links
6
Mind Map
7
Teachers' Notes Contents Student Worksheet
8-15 16-20
Summary
21
Rubrics of Assessment for learning
23
Flowchart & Crossword Puzzle
24
Interesting facts
25
Additional Resource Links
28
Unit – 12 Some p-Block Elements SYLLABUS COVERAGE 11.1
General Introduction
11.2
Group 13 elements
11.3
-
Electronic configuration
-
Inert pair effect
-
Reactivity
-
Compounds
Group 14 elements -
Electronic configuration
-
General properties
-
Catenation
-
Allotropic forms of carbon
-
Carbides
-
Compounds
1
LEARNING OUTCOMES At the end of this unit students would be able to –
Deduce the variation in oxidation states within Group 13 and Group 14.
Understand the reactions of boron and aluminium with air, halogens, acids and alkalis.
Comprehend the concept of catenation.
List the allotropic forms of carbon and describe their general characteristics, including a brief idea about fullerenes.
Compare the reactivity of silicon tetrachloride and carbon tetrachloride.
Describe the preparation, properties and structures of orthoboric acid, borax and diborane.
Understand the classification and structures of silicates.
Know the preparative methods and industrial importance of silicones.
2
Lesson Plan Matrix CONTENT
A. Warm up -
B. Pre-requisite
STEPS TO BE FOLLOWED
SKILL
TEACHER’S TIP
STUDENT’S TIP
DEVELOPED
Emphasize that within the p-block, the periodic trends are not as regular as amongst the sblock elements. A good number of irregularities in physical parameters, such as atomic radii, ionic radii and ionization enthalpy are observed in Group 13 and 14.
Unlike, the s-block elements, where all members are metals, the p-block houses metals, nometals and semimetals (metalloids). Hence the chemical reactivities vary a great deal within Group 13 and 14.
Imagination and visualisation, identification, infer, compare, analyse, correlation
Recapitulate the Recall the periodic periodic properties trends and reasons and trends. . behind the trends
Recall, Identification, comprehension
Analytical and problem solving skills, Creative thinking
Scientific and analytical thinking 11.1 General Introduction
Discuss the position of Group 13 and 14 elements in the periodic table. Emphasize that these elements have smaller size, higher ionization enthalpies and lower reactivities
The metallic character increases on going down the group. This is most evident in Group 14, where the first element (carbon) is a non-metal, the next two (silicon and germanium) 3
Recall, identification, infer, compare
11.2 Group 13 elements
11.3 Group 14 elements
than the corresponding elements of Group 1 and 2.
are metalloids, while the last two (indium and tin) are true metals.
Discuss the general trends within Group 13. Introduce the concept of inert pair effect. List important chemical reactions of boron and aluminium. Describe the preparation, properties and structures of some industrially important compounds of Group 13 elements.
The Group 13 elements are harder and less reactive than the s-block elements. A few compounds of gallium and indium find applications in semiconductor devices. Diborane and orthoboric acid have interesting structural properties, while borax is commercially important.
Student Activity 1
Student Worksheet 1
Emphasize the importance of catenation, explaining why it is more important for carbon than for the other members of the group. A description of the allotropic forms of carbon, both the crystalline and amorphous varieties. The variation in
Elucidate the reason as to why carbon forms such a large number and variety of compounds. The variation of metallic character within the group. Preparation and properties of different categories of carbides. Knowhow of silicon-based 4
Decisionmaking, observation, correlation, Scientific and analytical thinking
Organisation, identification, infer, compare, analyse, correlation
reactivities of the compounds of carbon and silicon. The basis of the classification of carbides. Industrial importance and structures of silicates and silicones.
polymers. Student Worksheet 2
Student Activity 2 C. Summary
Review the highlights of the chapter. Emphasize the importance of variable oxidation states, catenation and allotropy.
Solve the crossword puzzle. Understand why the variation of metallic character is more marked in Group 13 and 14, than in Group 1 and 2 and to what consequence.
Compare and contrast the properties of sand p-block elements.
Student Worksheet 3
5
Analyse, infer, application Selforganisation, selfdisciplined, dealing with new situations or problems, adaptability.
CROSS CURRICULAR LINKS
Biology-To examine the importance of carbon compounds in life processes.
Mathematics-To calculate the lattice energy of the compounds of those elements which show inert pair effect and compare the values for different oxidation states.
Environment-To describe the applications of silicon-based solar cells as devices for conservation of energy.
Physics-To highlight the utility of gallium, silicon and germanium in semiconductor devices.
Computers-To describe the significance of silicon chips in computer applications.
Geology-To study abundance of Group 13 and 14 elements under the earth.To follow the course of carbon cycle in nature.
PRE-REQUISITES Recall the following concepts already learnt in previous classes. (i)
Position of Group 13 and 14 elements in periodic table.
(ii)
Distinction between metals, non-metals and metalloids.
(iii)
Formation of ionic and covalent bonds.
(iv)
Variation of ionic character on the basis of Fajan’s rule.
6
MIND - MAP 1. Group 13 elements
2. Group 14 elements
Electronic configuration
Electronic configuration
Physical properties
Physical properties
Chemical properties
Chemical properties
Inert pair effect
Catenation
Reactivity
Allotropic forms
Compounds
Carbides
Compounds
7
Prerequisite Recapitulate the periodic table and the positioning of p-block. Discuss some periodic properties and trends.
11.1
General Introduction Emphasize that within the p-block, the periodic trends are not as regular as amongst the s-block elements. A good number of irregularities in physical parameters, such as atomic radii, ionic radii and ionization enthalpy are observed in Group 13 and 14. Discuss the position of Group 13 and 14 elements in the periodic table. Emphasize that these elements have smaller size, higher ionization enthalpies and lower reactivities than the corresponding elements of Group 1 and 2.
11.2
Group 13 elements Discuss the general trends within Group 13. Introduce the concept of inert pair effect. List the important chemical reactions of boron and aluminium. Describe the preparation, properties and structures of some industrially important compounds of Group 13 elements.
8
Tell the students to perform Student Activity 1 and Student Worksheet 1. Extension Some More Physical Properties of Group 13 Elements Melting points and Boiling points Fact
Explanation
In comparison to Group 2: The melting and boiling points of Group 13 are much higher than those of Group 2 elements.
The very high melting point of boron is due to its unusual crystal structure. The small size and high ionisation enthalpy makes boron a non-metallic element, thus, metallic bonding does not exist. The structure of boron is icosahedral (20-faced) with boron at all 12 corners.
Fig: Icosahedral structure of Boron Gallium also has an unusual structure. Ga has melting point of 30oC. In the structure of Ga, diatomic molecules exist which accounts for its low melting point. Trend in the group: The melting points of Group 13 elements do not show a regular trend. The boiling points of Group 9
The regular gradation of boiling point corresponds to the expected pattern as no unusual structures exist in liquid phase.
13 elements decrease regularly as we descend the group.
Figure 12.1 : Melting points of Group 13 elements
Figure : Boiling points of the Group 13 elements
Density Fact
Explanation
Trend in the group: Densities increase on descending the group.
This is due to increase in atomic mass of the element which outweighs the effect of increased atomic size. Thus the density increases on descending the group.
Figure 12.2 : Densities of the Group 13 elements 10
Standard reduction potential: The standard reduction potential, Eo(M3+ M),becomes more negative in going from B to Al indicating the increase in metallic nature from B to Al. After Al, the values become less and less negative and for Tl become positive indicating M3++ 3e- M becomes easier. This explains the +3 oxidation state becoming less stable in aqueous solution on descending the group. The Eo (M+| M) value for Tl is more negative than that of In indicating the higher stability of TI+ over In+. Anomalous Behaviour of Boron Boron differs from the other members of Group 13 because of (i)
small atomic size
(ii) high electronegativity (iii) high Ionisation enthalpy. The major points of difference are as follows: (i)
Boron is a non-metal and a bad conductor of electricity.
(ii) Boron exists in two allotropic forms i.e. crystalline and amorphous. (iii) The melting point and boiling point of boron are much higher than the other elements in the group. (iv) Boron is hard and almost unreactive at ordinary temperature. (v) Boron forms only covalent compounds because of its high electronegativity and Ionisation enthalpy.
Diagonal Relationship of Boron with Silicon Boron shows anomalous behaviour in its group because of its small size and non-availability of d-orbitals. Boron resembles silicon, the second member of the next group. 1.
Both boron and silicon do not occur in the free state but are found in the combined state mostly in the form of borates and silicates.
2.
Boron and silicon exhibit properties of non-metals and exist in allotropic forms.
3.
Boron and
silicon,
both
have 11
high melting
points
and
are
semiconductors. 4.
5.
Both form solid oxides, boron oxide B 2O3 and silica SiO2, which are acidic and dissolve in alkalies to form borates and silicates respectively. B2O3 + 6NaOH
2Na3BO3 + 3H2O
SiO2 + 2NaOH
Na2SiO3 + H2O
The hydroxides of boron and silicon, B(OH)3 and Si(OH)4 both are weak acids. B(OH)3 + 6NaOH Si(OH)4 + 2NaOH
6.
2Na3BO3 +3H2O Na2SiO3 + 3H2O
Both boron and silicon form several volatile and spontaneously inflammable hydrides called boranes and silanes respectively. The hydrides are readily hydrolysed. The lower hydrides can be obtained by the reduction of chlorides with LiAlH4. 4BCl3 + 3LiAlH4 3AlCl3 + 3LiCl + 2B2H6 SiCl4 + LiAlH4
7.
AlCl3 + LiCl + SiH4
The halides of both boron and silicon are covalent, volatile and hygroscopic. These are easily hydrolysed by water to boric acid and silicic acid, respectively. BCl3+ 3H2O
H3BO3 + 3HCl
SiCl4 + 4H2O
H4SiO4+ 4HCl
Borax bead test. When the glassy bead is mixed with some coloured cations such as Ni2+, Co2+, Cr3+, Cu2+, Mn2+, etc. and heated again, it gives characteristic coloured beads of the metaborate of different ions. The test is performed on a platinum wire with the salts containing these cations. On heating, the salts are converted into their oxides which form colouredmetaborates with boron oxide. The characteristic colour imparted to the bead gives an indication of metallic radical due to colouredmetaborate formation. This is known as the borax bead test. NiO + B2O3 Ni (BO2)2 Nickel metaborate (brown) 12
CoO + B2O3
Co(BO2)2 Cobalt metaborate (blue)
Cr2O3 + 3B2O3
2Cr(BO2)3 Chromium metaborate (green)
MnO + B2O3
Mn(BO2)3 Managanese metaborate (pink)
CuO + B2O3
Mn(BO2)2 Cupric metaborate (blue) Certain metaborates are reduced to the free metal in reducing flame by carbon. 2Cu(BO2)2 + C Cupric metaborate (blue) 2CuBO2 + C Metal (Red)
2CuBO2 + B2O3 + CO Cuprous metaborate (colourless) 2Cu + B2O3 + CO
Structure of Borates Structure of complex borate anions is difficult to be predicted from the stoichiometry of their compounds. However, they are generally cyclic or linear polymers. Structure consists of: a) Boron atom linked either to three oxygen atom (BO3 units) or four oxygen atoms (BO4 tetrahedron) b) Polynuclear anions are formed by corner-sharing of boron oxygen triangles or tetrahedrons.
13
11.3
Group 14 Elements Emphasize the importance of catenation, explaining why it is more important for carbon than for the other members of the group. A description of the allotropic forms of carbon, both the crystalline and amorphous varieties. The variation in reactivities of the compounds of carbon and silicon. The basis of the classification of carbides, structures of silicates and silicones. Tell the students to perform Student Activity 2 and Student Worksheet 2. Extension Some more Physical Properties of Group 14 elements Melting point: Fact
Explanation
Trend in the group: On descending the Group, the melting points decrease with the exception of Pb whose melting point is slightly more than Sn.
C has an extremely high melting point due to very strong C-C bonds in the network of C atoms in the diamond lattice. Si and Ge also have a diamond type of lattice and thus have a high melting point. The decrease in melting points from C to Si to Ge is due to the weakening of M-M bond due to increase in covalent radii of the element.
Figure 12.3 : Melting Points of the Group 14 Elements The melting point of Sn and Pb are low. They do not use all four electrons 14
for metallic bonding. BOILING POINTS Fact
Explanation
Trend in the group: On descending the group boiling points of Group 14 elements decrease.
As we descend the group the sizes of atoms increase and hence forces of attraction decrease, thus causing decrease in boiling point.
DENSITY Fact
Explanation
Trend in the group: The densities of Group 14 increase as we descend the group.
There is a greater increase in the atomic mass as compared to the atomic size and thus density increases on descending the group.
Structure of Trisilylamine The compound trisilylamine has the formula (SiH 3)3N. Electronic
1S
2S
2P
Structure of N (ground state) In trisilylamine, three sp2 orbitals are used for bonding, giving a planar triangular stnucture. The lone pair of electrons occupy a p orbital at right angles to the plane triangle. This overlaps with the empty d orbitals on each of the three silicon atoms, and results in bonding. This is known as bonding because the empty d-orbital gets a lone pair of electrons from the full p-orbitals. This shortens the bond length N - Si. Towards the end of the unit, review the highlights of the chapter. Emphasize the importance of variable oxidation states, catenation and allotropy. Compare and contrast the properties of s- and p-block elements. 15
STUDENT WORKSHEETS Student Worksheet 1 1.
Which of the following metal exists as a liquid in extreme summers? a) Boron b) Gallium c) Indium d) Thallium
2.
The compound MCl is more stable than MCl 3. M is – a) Boron b) Aluminium c) Gallium d) Thallium
3.
The hydride of which element possesses 2-electron 3-center bonds? a) Boron b) Aluminium c) Indium d) Thallium
4.
Which of the following halides show back bonding? a) BCl3 b) AlCl3 c) GaCl3 d) CCl4
5.
Which is the strongest Lewis acid? a) BF3 b) BCl3 16
c) BBr3 d) BI3 6.
Compare the structure of aluminium(III) chloride in solid state and in aqueous solution.
7.
Write chemical equations for the reaction of aluminium with (a) air; (b) hydrochloric acid; and (c) sodium hydroxide.
8.
Why is diborane referred to as an electron deficient compound?
9.
Write a note on ‘inert pair effect’.
10.
Draw the structure of orthoboric acid. Answers 1.
b
2.
d
3.
a
4.
a
5.
d
17
Student Worksheet 2 1.
Carbon shows the property of catenation because – a) It does not possess d orbitals b) It is reactive towards most non-metals c) It readily forms carbides d) The C – C bond strength is very large
2.
The largest number of allotropic forms are shown by – a) Carbon b) Silicon c) Germanium d) Tin
3.
Which of the following is the most unstable chloride? a) CCl4 b) SiCl4 c) SnCl4 d) PbCl4
4.
Graphite forms intercalation compounds most readily with – a) Lithium b) Sodium c) Potassium d) Rubedium
5.
Asbestos is a form of – a) Silicone b) Silicate c) Carbide d) Fullerene 18
6.
Explain why carbon tetrachloride is inert, while silicon tetrachloride is extremely reactive.
7.
How are carbides classified? Give two examples of each type.
8.
Differentiate between the characteristics of graphite and diamond.
9.
Write chemical equations for the reaction of lead with (a) concentrated sulphuric acid; (b) concentrated nitric acid; and (c) sodium hydroxide.
10.
Outline the method for synthesis of cross-linked silicones. What is the commercial importance of silicones?
Answers 1)
d
3)
c
2)
d
4)
b
19
Student Worksheet 3 1.
Explain why BF3 has no dipole moment, while PF3 has a substantial dipole.
2.
Giving reason, explain why tin(II) chloride is a solid, while tin(IV) chloride is a liquid.
3.
Why do BF3 and BrF3 have different geometries?
4.
Explain why carbon dioxide is a gas, but silicon dioxide is a solid.
5.
The strength of orthoboric acid increases on adding glycol. Why?
6.
Explain why there is no back bonding in Aluminium chloride.
7.
Giving reason, explain why doesn’t BCl3 dimerize like AlCl3.
20
SUMMARY Group 13 Physical Property
Trend in the Group
1. Electronic configuration ns2np1 2. Atomic radii and ionic radii
Increase
3. Metallic radii
does not decrease linearly
4. Ionisation energy
does not increase smoothly (d block contraction)
5. Oxidation states
+3 state and +1state (inert pair effect)
6. Electropositive character
increases (B to Al) and then decreases (Al to Tl)
7. Nature of bonds (ionic bonds)
Increases
Chemical Property
Trend in the Group
1. Reaction with water
No reaction
2. Oxides - Acidic Character
Decreases
3. Halides - p -p
BF3> BCl3> BBr3
bond
Group 14 Physical Property
Trend in the Group (on descending)
Trend in Comparison to Group 15
1. Atomic radii
Increases
decreases
2. Ionisation energy
decreases (C > Si >Ge>Sn
increases
3. Oxidation states
+4 (stability decreases), +2 (stability increases, Inert Pair)
4. Electropositivity
Increases
decreases
5. Electronegativity
Decreases
increases
6. Catenation
Decreases 21
Chemical Property
Trend in the Group
1. Hydrides
Stability decreases
2. Halides
MX4 - covalent - tetrahedral
3. Oxides
MO2 - dioxides, MO - monoxide (except silicon)
4. Silicones
Organosilicon compounds (R2SiO units) held by Si - O- Si
Boron compounds are electron deficient.
BH3 has a dimeric nature and exists as diborane. It has four normal covalent B H bonds i.e. two centre, two electron bonds which lie in same plane and two bridge bonds; B ... H ... B i.e. three centre two electron bonds or banana bonds.
Acidic strength of boron trihalides: BI3> BBr3> BCl3> BF3.
Boron on strong heating gives a glassy bead called borax bead which forms the basis of borax bead test.
Boric acid is a weak monobasic acid and it is not a proton donor but acts like Lewis acid. B(OH)3 + H – OH
[B(OH)4]–+H+
Carbon shows various allotropic forms like diamond, graphite, coke, charcoal, lampblack, etc. Fullerene is the
60C
allotrope of carbon. It consists of 20 six
membered and 10 five membered rings.
Carbon reacts with elements of lower or equal electronegativity fo form ionic, covalent and interstitial carbides.
Carbon has maximum tendency for catenation due to stronger C - C bonds.
22
Rubrics of Assessment for Learning Parameter
Beginning Approaching (1) (2)
Write the valence shell electronic configuration of Group 13 and 14 elements. Comment on the variation of oxidation states within Group 13 and Group 14 elements. Comment on the significance of catenation. How does catenation vary within Group 13. Discuss the important allotropic forms of carbon Explain the structure of diborane. Write the structures of the trichlorides of boron and aluminium in solid states.. Comment on the basis of classifying carbides. List the important classes of silicates. Compare the reactivity of carbon tetrachloride and silicon tetrachloride. Outline the applications of silicones.
23
Meeting (3)
Exceeding (4)
FLOW CHART 2.
1. General characteristics of p-block elements and their position in the periodic table.
Group 13 elements. Physical and chemical properties. Inert pair effect. Industrially important compounds.
3. 3.
4.
Group 4 elements. Physical and chemical properties. Catenation. Allotropic forms of elements. Industrially important compounds.
Comparison and contrast between members of Group 13 and 4, with special reference to the structure of their compounds.
CROSSWORD 1.
A member of Group 13 known for conductivity related applications. ALUMINIUM
2.
Hardest known substance. DIAMOND
3.
Conducting allotropic form of carbon. GRAPHITE
4.
A compound with banana bonds. DIBORANE
5.
Other name for intercalation compounds. LAMELLAR
6.
Inorganic benzene. BORAZINE
7.
A boron-based compound synthesized from colemanite. BORAX
8.
Compounds containing boron and a metal. BORIDES
9.
A process by which atoms of an element indulge in self-linkage. CATENATION 24
10.
An element used in storage batteries. LEAD
11.
Binary compounds of carbon. CARBIDES
12.
Common name for C60 fullerene. BUCKYBALL
13.
Silicates based on discrete tetrahedral units. ORTHOSLICATES
14.
Metal which forms a liquid tetrachloride. TIN
15.
Used for making solar cells. SILICON
16.
Member of Group 13 which shows inert pair effect. THALLIUM
17.
An ore of aluminium. BAUXITE
18.
An assemblage of carbon atoms to give cylindrical structure. NANOTUBE
19.
An extremely poisonous gas whose molecules contain only carbon and nitrogen. CYANOGEN
20.
Silicone-based polymers used as a heat transfer media. SILICONES
MNEMONICS Boring Aluminum Galley’s Indigestible Tally-list (B, Al, Ga, In, Tl) Can Silly Getty Snatch Pebbles (C, Si, Ge, Sn, Pb)
INTERESTING FACTS
Boranes: Although boron is expected to form hydrides like BH3, this compound is unstable at room temperature. However, large number of higher hydrides of boron is known. Boranes fall into two series: Nido-boranes with a general formula BnH(n+4) Arachno-boranes with a general formula BnH(n+6). This is a less stable series. The members of the series are as follows:
25
Table: Two series of Boranes Nido-boranes : BnH(n+4)
Arachno-boranes: BnH(n+6)
B2H6 diborane
B4H10tetraborane
B5H9pentaborane - 9
B5H11pentaborane - 11
B6H10hexaborane - 10
B6H12 hexaborane - 12
B8H12octaborane -12
B8H14octaborane - 14
B10H14decaborane
B9H15nonaborane or enneaborane
Out of these, diborane is one of the simplest and most studied of the hydrides. It is an important reagent in synthetic organic chemistry. The fullerene saga In 1996, the noble prize in chemistry was shared by two American scientists named Richard.E.Smalley and Robert.F.Curl of Rice university, Huston, Texas, USA and a British scientist. Harold W. Kroto for their discovery of fullerenes in 1985. This fascinating discovery has excelled the interests of chemists, phycists and material scientist in chemistry. Kroto had shown that linear chain molecules of carbon and nitrogen i.e. polyynesHC nN were present in interstellear space. So he got interested in knowing the method to produce long chains in the laboratory. Smalley had built up an apparatus to produce clusters of virtually any element in periodic table by 'leaser vaporization supersonic beam' technique. Curl was an expert in laser spectroscopy of molecules and transient species Now, Kroto mentioned this idea to his friend Curl and Curl who was collaborating Smalley from 1982 on semi-conductor clusters told him that Smalley had the apparatus suited to produce carbon clusters. Thus, all the three came together and carried out their research in Rice University in 1985. Laser evaporation of graphite didn't give any evidence for the formation of linear molecules. In addition, other carbon clusters containing 40 to 100 of carbon atoms were formed. By the use of mass spectrometry, they noticed 26
that one peak at atomic unit (U) 720 corresponding to C60 was predominantly present in evaporation experiments. Another peak, which was at 840 u, corresponded to C70. This molecule was named Buck minsterfullerene in honor of American architect Buchminster Fuller, who designed geodesic domes. Several other experiments were carried out in different countries and the general name 'fullerene' was given to these species formed by the condensation of carbon vapour. They care also called bucky balls or tubes. Another breakthrough came in 1990 when Kractechnor and Huffman found a practical method for the production of fullereness in large quantities. They passed an electric arc through graphite rod in an atmosphere of helium to produce carbon root. The extraction of soot with an organic solvent gave a soluble fraction which contained C60 in large quantity and smalle fractions of C70 and other fullerenes. Then, C60 and C70 were isolated by chromatography. C70 has the shape like a rugby ball. Carbon nanotubes are also produced by electric arc evaporation of graphite which consists of cylindrical tubes formed by graphite layers which are capped by fullerne like hemispheres. These bucky balls have applications in catalysis, nanotechnology and lectronics. Kroto calls C60 as 'the celestial sphere that fell on earth'.
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ADDITIONAL RESOURCE LINKS en.wikipedia.org/wiki/Boron_group http://www.rsc.org/chemsoc/visualelements/pages/data/intro_groupiii_data. html en.wikipedia.org/wiki/Carbon_group http://www.tulane.edu/~inorg/PDF%20Files/Group%2014%20Elements.pdf chemistry.about.com/od/elementgroups/a/Carbon-Family.html
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