BSc in Applied Biotechnology
BO0034 - CHEMISTRY (ORGANIC AND PHYSICAL)
Summer 2015 (4 Credit)
No Q 1
Marks Total Marks 10
Define an orbital. List and discuss the shapes of orbitals. ( Unit 2 ; Section 2.10 )
Defining Orbital An orbital is the region of space around the nucleus within which the probability of finding an electron of given energy is maximum.
Listing the shapes of orbitals 1) s-orbital 2) p-orbital 3) d-orbital
Discussing the shape of s-orbital • The s-orbitals are non-directional and symmetrical about the nucleus and only one orientation is possible.
• The size of an s-orbital depends upon value of the principal quantum number n • The 1s and 2s orbitals are the shapes of s-orbitals • The 2s-orbital has a spherical shell within this orbital where the probability of finding the electron is zero which is called as node or nodal surface, it has only one spherical node.
Discussing the shapes of p-orbitals • p-orbitals can have three possible orientations which are equal in energy but differ in their orientations.
• p-orbital consists of two lobes which are symmetrical about a particular axis. • Depending upon the orientation of the lobes, these p-orbitals are denoted as 2px , 2pyand 2pz accordingly. • p-orbitals have dumb bell shape and have directional character.
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• The probability of finding the electron is equal in both the lobes. • The p-orbitals of higher energy levels have similar shapes although their size are bigger. Discussing the shape of d-orbital • d- orbitals can have five orientations which are represented by dxy, dyz, dzx, dx2-y2 and dz2.
• The dxy, dyz and dzx orbitals have clover leaf shape but they lie in XY, YZ and ZX planes respectively. • The dz2 orbital is symmetrical about Z-axis and has a dumb - bell shape with a doughnut shaped electron cloud in the centre. • The dx2-y2 orbital is also clover leaf shaped but its leaves are directed along the X and Y- axis. • The d-orbital has four lobes in any nd orbital lies in the fact that the d - orbitals have two nodes.
Define hybridisation. Explain sp, sp2 and sp3 hybridisation.
( Unit 4 ; Section 4.6 )
Definition of hybridisation Hybridisation is the process of mixing the atomic orbitals to form new orbitals suitable for bonding.
Explaining sp hybridisation • sp hybridisation involves the mixing of one s and one p orbital resulting in the formation of two equivalent sp hybrid orbitals.
• The suitable orbitals for sp hybridisation are s and pz, if the hybrid orbitals are to lie along the z-axis. • The sp hybrid orbitals has 50% s-character and 50% p-character. • If a molecule in which the central atom is sp-hybridised and linked directly to two other central atoms possesses linear geometry. This type of hybridisation is also known as diagonal hybridisation. • The two sp hybrids point in the opposite direction along the z-axis with projecting positive lobes and very small negative lobes, which provides more effective overlapping resulting in the formation of stronger bonds.
Explaining sp2 hybridisation • sp2 hybridisation involves one s and two p-orbitals in order to form three equivalent sp2 hybridised orbitals.
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• For example, in BCl3 molecule, the ground state electronic configuration of central boron atom is 1s22s22p1. • In the excited state, one of the 2s electrons is promoted to vacant 2p orbital as a result boron has three unpaired electrons. • These three orbitals (one 2s and two 2p) hybridise to form three sp2 hybrid orbitals. • The three hybrid orbitals so formed are oriented in a trigonal planar arrangement and overlap with 2p orbitals of chlorine to form three B-Cl bonds. • The geometry of BCl3 is trigonal planar with Cl-B-Cl bond angle of 120°.
Explaining sp3 hybridisation • In CH4 molecule the one s-orbital and three p-orbitals of the valence shell are mixed to form four sp3 hybrid orbital of equivalent energies and shape.
• In each sp3 hybrid orbital there is 25% s-character and 75% p character. • The four sp3 hybrid orbitals so formed are directed towards the four corners of the tetrahedron. • The angle between sp3 hybrid orbital is 109.5°
( Unit 3 ; Section 3.6 )
Define Ionization enthalpy. Discuss the factors that influence ionization enthalpy of an atom.
Definition of Ionization enthalpy The energy required to remove an electron from an atom is known as ionization enthalpy (IE) or ionization energy.
Discussing the factors influencing ionization enthalpy of an atom 1) Size of the atom 2) Charge on the nucleus 3) Screening effect of inner electrons 4) Penetration effect of electrons 5) Effect of half-filled and completely filled sub-levels
Explain the IUPAC rules for naming branched alkanes, alkenes and alkynes using examples.
( Unit 10 ; Section 10.3 )
explaining IUPAC rules for naming branched alkanes 1) Find the longest continuous carbon chain present in the molecule and use the name of that chain as the parent name. 2) If two different chains of equal length are present, select the chain with the
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larger number of branch points as the parent. 3) The complete name of the branched alkane is written as one word by prefixing the name of the alkyl group to the name of the parent alkane. 4) When two or more different alkyl groups are present on the parent chain, assign position – number to each and list alphabetically with the hyphen in between 5) When two or more identical groups are present, indicate this by the use of the prefixes di, tri, tetra, etc., immediately before the alkyl group.
Explaining the IUPAC rules for naming branched alkenes 1) The longest continuous chain is selected that contains both carbons of the double bond and the name of the corresponding alkane name is changed from -ane to -ene 2) The carbon atoms are numbered in the chain beginning from the end which is nearer to the double bond. 3) The name and position of the substituent attached to the long chain is indicated
explaining IUPAC rules for naming branched alkynes 1) The hydrocarbons with the carbon – carbon triple bond (C C) are called alkynes. 2) The functional group of alkynes is C C which is designated by the suffix ‘yne’. 3) The longest chain containing both carbons of the triple bond as the parent chain are selected. 4) The position of the triple bond by prefixing number of the first carbon of the triple bond is indicated.
Describe the structure and properties of benzene.
( Unit 11 ; Section 11.5.1 )
Describing the structure of benzene • The molecular formula of benzene indicates the presence of unstauration and the Kekule proposed alternate single and double bonds between carbon atoms.
• It does not undergo the usual reactions of alkenes such as addition, oxidation and reduction. • It does not decolourize bromine water or potassium permanganate solution, which is characteristic of unsaturated compounds. • The structure of benzene account for the formation of a single mono substituted product and three di-substituted isomers (-O, -M and P-) since all six carbon atoms and all six hydrogen atoms are equivalent. • It is a flat hexagonal molecule with all carbon and hydrogen lying in the same plane with a bond angle of 120o. Each carbon atom is sp2 hybridised.
Describing the properties of benzene 1) Physical properties: colour less, insoluble in water but miscible with organic solvents such as benzene, chloroform, etc., in all proportions. Ver : BScBT_0708
2) Chemical properties: Nitration Sulphonation Oxidation Reduction Halogenation Q 6
Discuss the physical properties of liquids. (Unit 8 ; Section 8.3 )
10 important physical properties of the liquids are listed below. 1) Vapour pressure: • The vapour pressure of a liquid is defined as the pressure exerted by the vapour on the surface of the liquid when there is equilibrium between the two phases. • The vapour pressure of a liquid depends upon the temperature. • As the temperature rises, the kinetic energy of the molecules increases. • With the result more number of molecules escape to the vapour phase increasing vapour pressure. 2) Boiling points: • The boiling point of a liquid is that temperature at which the vapour pressure of the liquid becomes equal to the external pressure. • If the external pressure is one atmosphere or 760mm of Hg it is known as normal boiling point. • Different liquids have different boiling points depending upon the extent of the forces of attraction between the molecules and also the presence of hydrogen bonding. 3) Surface tension: • Surface tension is another property of a liquid which arises due to the intermolecular forces of attraction. • In fact the surface tension is the phenomenon which explains the interesting property of liquids like capillary rise. This also explains why a drop of water assumes a spherical shape. 4) Viscosity: • Some liquids like alcohol and water can be poured into a vessel quickly.
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• Some liquids such as castor oil and honey can not poured so quickly. • These liquids take more time for the flow. • The difference in the flow is due to the difference in the viscosity of the liquids. • The viscosity of a liquid is related to its fluidity. In fact the viscosity is the reciprocal of the fluidity. 5) Refraction
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