CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES

Transcription

1 CCP 1 CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES Syllabus : Modern periodic law and present form of the periodic table, s, p, d and f block elements, periodic trends inproperties of elementsatomic and ionic radii, ionization enthalpy, electron gain enthalpy, valence, oxidation states and chemical reactivity.

2 CCP 2 C O N C E P T S C1 Dabereiner : grouped elements in Traids. He pointed out that there were sets of three elements (Ttaids) which showed similar chemical properties. He also noted that the atomic weight of the central element of the Triad was approximately the mean of the atomic weights of the other two members. The properties of the middle element were in between of those end members. e.g. Li, Na, K, Ca, Sr, Ba or Cl, Br, I etc. John Newland : He developed a law of octaves. He observed that similar elements are repeated at 8th place like the 8th note of music. The elements are arranged in the order of increase of atomic weights. Similar element means that physical & chemical properties of element will be same. e.g. Li has the same property as of Na. Lother Meyer arrangement : He studied the physical properties such as atomic volume, melting point and boiling points of various elements. On this basis he poltted a graph between Atomic volume (cm 3 ) Vs. Atomic weights. (iv) (v) (vi) (vii) (viii) (ix) (x) Observation : The most electropositive alkali metals (Li, Na, K, Rb and Cs) occupy the peaks on the curve. The less strongly electropositive elements i.e. alkaline earth metals (Be, Mg, Ca, Sr and Ba) occupy the descending positions on the curve. The most electronegative elements i.e., halogens (F, Cl, Br and I) occupy the ascending positions on the curve. On the basis of these observations, Lother Meyer proposed that the physical properties of the elements are a periodic functions of their atomic weights. Mendeleev s Periodic law and table : Mendeleev arranged all the elements in the order of increase of atomic weight. A table formed with the help of classification of elements is called periodic table. The method of arranging similar elements in one group and seprating them from dissimilar elements is called classification of elements. He prepared the periodic table on the basis of periodic law i.e., The properties of elements are periodic function of their atomic weight. Mendeleev s periodic table conists of seven horizontal rows known as periods and nine vertical column known as groups. Periods : Out of seven periods, first three periods are short periods while the fourth, fifth and sixth periods are called long periods. There are nine groups in all including 8th group of transition elements and zero group of inert gases. All the group from I to VII (except zero and VIII) were divided into sub-groups. The group number represents the valency. The elements of same sub group resemble to each other more closely and differ from other sub groups. He predicted the properties of the missing elements from the known properties of the other elements in the same group. e.g. gallium and germanium were not discovered at that time. He named these elements as Eka-Aluminium and Eka-silicon.

3 Defects in Mendeleev s Periodic Table : CCP 3 1. Position of Hydrogen : Hydrogen resembles both the alkali metal and halogen. Hence its position in periodic table is undecided. 2. Position of Isotopes : According to Mendeleev s periodic table, isotopes should occupy different positions in the periodic table, but this is not so. 3. Position of VIII group elements : Nine elements in the VIII group do not fit into the system. 4. Positions of Lanthanides and Actinides : Their position was not justified according to the periodic law and cannot be arranged in the order of their increasing atomic weight. 5. Dissimilar elements placed in the same group : Alkali metals (Li, Na, K etc.) are placed with coinage metals (Cu, Ag, Au). 6. Similar elements placed Apart : Chemically similar elements like Cu and Hg, Ag and Ti, Au and Pt have been placed in different groups. 7. Anomalous pair of elements : Some elements of higher atomic weight have been placed before the elements of lower atomic weight. e.g. Argon (At. wt. = 39.9) has been placed before potassium (At. wt. = 39.1); cobalt (At. wt. = 58.94) is placed before nickel (At. wt. = 58.69); Tellurium (127.5) has been placed before iodine (126.9). (e) Modern Periodic law and the present form of periodic table : As a result of modern researches it is estabished that atomic number is a fundamental property not the atomic weight. Thus this led Moseley to change the basis of calssification of elements from atomic weight to atomic number. The modern periodic law given by Moseley is : The properties of elements are periodic functions of their atomic numbers, i.e., if elements are arranged in the order of their atomic numbers. Similar elements are repeated after regular intervals. He also gave the following formulae i.e., = a(z b) ; = frequency of X-rays (iv) (v) (vi) (vii) C2 a, b = constant for all lines in a given series of X-rays z = atomic number Now we will discuss why elements with similar properties reoccurs after certain regular intervals. Cause of Periodicity : The cause of periodicity in properties is the repeatition of similar outer electronic configuration at certain regular intervals which indeed determines the physical and chemical properties of the elements and their compounds. A modern version of table contains horizontal rows known as periods (which Mendeleev called series). Elements having similar outer electronic configuration in their atoms are grouped in vertical columns; these are referred as Groups or Families. According to IUPAC (International Union of pure and Applied Chemistry), the groups are numbered from 1 to 18 replacing the older notation of groups O, IA, II A... VIII B. There are seven periods (three short periods and four long ones). The first period contains 2 elements. The subsequent periods consists of 8, 8, 18, 18 and 32 elements respectively. The 7th period is incomplete. Till now elements upto 112 and 114 have been discovered. Elements with z = 113, 115 and beyond are not known. Arrangement of Elements in Periodic Table is according to Electronic Configuration of the Elements : Electronic configuration in Periods : Each successive period in the periodic table is associated with the filling of next higher principal energy shell i.e. n = 1, n = 2 etc. Number of atomic orbitals in each period is twice the number of atomic orbitals available in the energy level is being filled. The first period starts with the filling of the lowest energy level (1s) and has the two elements hydrogen (1s 1 ) and helium (1s 2 ).

4 (iv) (v) (vi) (vii) (viii) (ix) (x) (xi) C3 (iv) (v) (vi) (vii) Second period starts with lithium. CCP 4 The third period begins with sodium and added electrons enters a 3s orbital. This shell has nine orbitals (one 3s, three 3p and five 3d) but 3d orbital are of higher energy than 4s according to (n + l) rule. Therefore 3d orbitals are only filled after filling the 4s-orbitals. Thus it contains only eight elements. In the fourth period, the filling of electrons is in the fourth energy level i.e., n = 4. It starts with 4s. But in this filling of 4d and 4f orbital does not takes place. After filling 4s orbital, filling of 3d orbital and then 4p orbitals takes place. 4d and 4f are of higher energy than 5s. Thus it contains 18 elements. In the fifth period the filling of electrons starts with 5s orbital and then 4d orbitals are filled and then three 5p orbitals and filled. Sixth Period : Corresponds to filling of sixth energy level i.e. n = 6. In this period filling takes place in (one 6s, seven 4f, five 5d and three 6p) orbitals.there are 16 orbitals are available, thus 32 elements can be there. Filling up of the 4f orbital begins with cerium (z = 58) and ends at lutetium (z = 71) to give the 4f-inner transition series called the Lanthanoide Series. They are placed at the bottom of the periodic table. Similar to the sixth period, the seventh period corresponds to the filling of seventh energy shell i.e. n = 7. It is also expected to contain thirty two elements corresponding to filling of sixteen orbitals i.e. one 7s, seven 5f, five 6d and three 7p. Filling up of 5f orbitals after actinium (z = 89) gives the 5f inner tansition series known as Actinoid Series. Thus 4f, 5f transition series of elements are placed seprately in the periodic table to maintain its structure. Group wise electronic configuration Elements in the same vertical column or group have similar electronic configuration, have same number of electrons in the outer orbitals and have similar properties. Types of elements : s-, p-, d-, f- blocks -s Block elements : These elements contain 1 or 2 electrons in the s-orbital of their respective outer most shell. The elements of group 1 having outer-most electronic configuration ns 1 are called as alkali metals. The elements of group 2 having outer-most electronic configuration ns 2 are are called alkaline earth metals. Properties of s- block elements : They are reactive metals with low ionization energy. They lose the outermost electron readily to form +1 oxidation state in case of alkali metals. Alkaline earth metals can loose two electrons to aquire +2 oxidation state very easily. Metallic character and reactivity increases as we move down the group. The compounds of s-block are predominantly ionic with exception of Be (beryllium) P-block Elements : These elements contain 1-6 electrons in the P-orbital of their respective outermost shells. General electronic configuration of outermost shell is ns 2 np 1-6, where n 2-7. (iv) (v) (vi) (vii) (viii) (ix) These include elements belonging to group of 13, 14, 15, 16, 17 and 18 excluding helium. Properties of P-Block Elements : All the orbitals in the valence shell of the noble gases are completely filled by electrons. Thus it is difficult to alter this stable arrangement by addition or removal of electrons. Thus noble gases exhibit low chemical reactivity. Group - 17 elements are known as halogens and then have high negative electron gain enthalpy. Similarly group - 16 elements i.e., oxygen family are also known as chalcogens, have high tendency to gain electrons. The non-metallic character increases as we move from left to right in a period. Metallic character increases as we move down the group. Their ionization energies are higher than s-block elements. They mostly form covalent compounds. Some of them show more than one oxidation states in their compounds.

5 CCP 5 d-block Elements : These elements characterise by filling of inner d-orbital by electrons and therefore referred to d-block elements. General electronic configuration of d-block elements is (n 1) d 1-10 ns 0-2. (iv) (v) (vi) (iv) (v) C4 They are the elements belonging to 3 to 12 groups. Properties of d-block Elements : There ionization energies are between 5 and p-block elements. They show variable oxidation states. They form both ionic and covalent compounds Their compounds are generally coloured and paramagnetic. Most of transition metals form alloys. Most of transition elements are used as catalyst i.e., V, Cr, Mn, Fe, Co, Ni, Cu etc. Exception : Zn, Hg, Cd have (n 1)d 10 ns 2 electronic configuration, do not show most of properties of transition elements as they have complete d subshell and in them last electron enters the s-subshell not the d-subshell. Similarly of Zn, Cd, Hg with transition elements are : they form complexes like d-block elements. they form covalent compounds. first ionization energies are much higher f-block Elements : The two rows at the bottom of periodic table called Lanthanoids and Antinoids have outer most electronic configuration as : (n 2)f 1-14 (n 1)d 0-1 ns 2 Last electron enters the f-subshell. Thus two series elements are called f-block elements or inner-transition elements. Properties of f-block elements : They are all metals. They show variable oxidation states. There compounds are generally coloured. Most of the elements of actinide series are radioactive. In this series after uranium elements are called as transuranium elements. Classification of periodic table can be the basis of metals and non-metals. Properties of Metals They are good conductors of heat and electricity They are usually solids at room temperature They are malleable (can be flattened into thin sheets by hammering) and ductile (can be drawn into wires) Properties of Non-Metals They are bad conductor of heat and electricity They are usually solids or gases at room temperature They cannot be drawn into thin sheets or wires. * Metallic character increases down the group. * Metallic character decreases along the period. * The change from metals to metals in periodic table is not abrupt. The elements on the border line are semimetals or metalloids e.g. (Si, As, Sb, Te). C5 Prediction of period, group and block of given elements : Period of an element corresponds to principal quantum number of the valence shell. The block of an element is type of orbital which receives the last electron. Group is predicted as follows : for s-block elements : group number is equal to the number of valence electrons.

6 for p-block elements : group number is equal to 10 + number of valence electrons. CCP 6 for d-block elements : group number is equal to number of electrons in (n 1) d subshell + number of electrons in valence shell (nth shell) C6 Periodic trends in properties of elements : 1. Atomic radii : is the distance from the centre of nuclei to the point upto which the density of electron cloud is maximum. It is of four types : (iv) covalent radii vander wall radii metallic radii Ionic radii Covalent radii : r covalent = ½ [Internuclear distance between two covalently bonded atoms of same molecule] = ½ [bond length] Vander wall radii : r vander wall = ½ [Internuclear distance between two non-bonded atoms] of different or neighbouring molecules Metallic radii : = ½ [internuclear distance between two adjacent atoms in the metallic lattice] Variation of Atomic radii in periodic table : 1. Along the period it decreases as nuclear charge increases. Exception : The size of atoms of inert gases are however larger than the halogen elements. Reason : As we move along the period charge increases while the number of shells remain the same thus along the period size decreases. 2. Along the group the atomic radii of elements increases with increase in atomic number as we move from top to bottom of group. Reason : As we move down the number of shell increases thus distance between the outer electrons and nucleus increases. Also with increase of atomic number the nuclear charge down the group increases. Thus atomic radii should decreases, but effect of increased nuclear charge is reduced due to screening or sheilding effect on the valence electrons by the electrons present in the inner shells. Comparison of the ionic radii with atomic radii of same atom Mg > Mg 2+ Reason : In Mg n p = 12, 12 n e Mg 2+ n p = 12, 10 n e Thus in Mg 12 protons are attracting by the 12 electrons outer nuclear part. Whereas in Mg 2+ the 12 protons are attracting 10 e outside the nucleus thus 12 protons will attract 10 e electrons more strongly thus size of Mg 2+ decreases as compared to Mg.

7 CCP 7 * Atoms or ions with same electronic configuration are called isoelectronic. If we consider a series of isoelectronic species (atoms or ions) then size decreases with increase of atomic number. e.g. O 2, I, Ne, Na +, Mg 2+ (1.40) (1.36) (1.31) (0.95) (0.65) Atomic number * The size of same cation decreases with increase of magnitude of positive charge i.e. Fe 3+ is smaller than Fe 2+, Cu 2+ is smaller than Cu + so on... Ionisation Energy First I.E. : Amount of energy required to remove a single electron from the outer shell of a neutral gaseous atom. M(g) M + (g) + e... IE 1 M + M 2+ + e...ie 2 (IE 2 ) Second Ionisation Energy : Amount of energy required to remove the second electron from an atom who has already lost one electron. IE 3 > IE 2 > IE 1 As the number of electrons in outer shell decreases so attraction of nucleus for remaining electrons increases thus I.E. increases. Trends of first I.E. along the period and down the group is as follows : First I.E. decreases as we move down the group. Reason is that as we move down the group no. of shell increases thus nuclear attraction decreases. Although nuclear charge also increases but its effect is weakend by sheilding supplied by the inner shells to the outer most shell. As we move along the period ionisation energy increases. The reason for this is because of decrease of size of atom along the period. As the number of electrons are added to same shell along the period thus nuclear attraction for the outer electrons increases with increase of nuclear charge. Exception : (1) I.E. (B) < I.E. (Be) Electronic Configuration : B = 1s 2 2s 2 2p 1, Electronic configuration Be = 1s 2 2s 2 As in Be e is to be removed from completely filled shell thus its I.E. is more than B. Here is extra stability of subshell is the cause of this irregularity (2) I.E. of O < I.E. N Electronic configuration N = 1s 2 2s 2 2p x 2p y 2p z O = 1s 2 2s 2 2p 2 z 2p x 2p y The extra stability of half-shell is cause of irregularity in IE pattern. (3) I.E. of Al < I.E. of Mg Electronic configuration Al = 1s 2 2s 2 2p 6 3s 2 3p 1 Mg = 1s 2 2s 2 2p 6 3s 2

8 CCP 8 * The electrons in different orbitals (s, p, d, f) beloging to the same energy level experience different pull of the nucleus. The I.E. for pulling out an s-electron is maximum and it decreases in pulling out p-electron. Hence we can say that I.E. for pulling out an electron from a given energy level decreases in the order s > p > d > f orbitals. Electron Affinity : It is defined as energy given out when an extra electron is taken up by a neutral gaseous atom. X(g) + e X (g) E. A measures the tightness with which an atom binds an extra electron to it. E.A. decreases down the group, because an atom gets larger, the attractions of positive nucleus for an outside electron decreases. Exception : E.A. of F < E.A. of Cl Reason : It is due to extremely small size of F atom as compare to Cl atom. Extra electron create strong electron-electron repulsion among all the electrons. Along the period : Along the period electron affinity increases as we move from left to right. E.A. of noble gases are zero. E.A of N and Be atoms are quite low due to extra stability of half filled orbitals (p 3 in N & s 2 in Be) After taking up an extra electron an atom becomes negatively charged (anion) and now second electron is to be added to it. The anion will repel the incoming of an electron and an additional energy will be required to add it to the anion. First E.A. negative (energy released) Second E.A. positive (energy released) Electronegativity : It is the measure of the ability of an atom in a combined state (i.e. in a molecule) to attract itself to the electrons within a chemical bond or tendency to attract bond pair towards itself. * Non-metals have high value of electronegativity than metals. F, O, N & Cl are highly electronegative than [k, Rb, Cs] (metals) which are electropositive in nature. * Electronegativity along the period increases & down the group decreases. * It is measured with the help of pauling scale & mulliken scale. Screening (sheilding) effect : In d-block elements (transition element) while writing electronic configuration of elements, it is seen that new electrons are added to inner shells i.e. penultimate shells. Thus nuclear attraction for out electons gets affected. As the new electrons enter the inner shells they tend to sheild or screen the outer shell electrons from nucleus and thus decreases the nuclear attractive force. This is called as screening effect. Due to this effect, the atomic size of transition elements remain same as we move along the period which should decrease as we move from left to right. Thus ionisation energy, electron affinity and other properties remains nearly same as we move along the period. C7 Hydration and Hydration Energy : Hydration energy is the enthalpy change that accompanies the dissolving of one mole of gaseous ions in water. Li + (g) + H 2 O [Li(H 2 O)] +, H = 806 kj mol 1 Size of the ion and its charge determines extent of hydration. Greater the charge, smaller the size of the ion, greater the attraction for the lone pair of O of H 2 O, hence greater the extent of hydration and hence greater the hydration energy. size of the hydrated ions increases, ionic mobility decreases [heavier (hydrated) ions moves slower]

9 C8 Acid-Base character of oxides : CCP 9 On moving across a period, the basic character of the oxides gradually changes first into amphoteric and finally into acidic character. On moving down the group, reverse behaviour is observed, i.e., from more acidic to more basic. Oxides of the element M in H 2 O produce MOH If electronegativities difference of M and O is greater than that of H and O in H 2 O then MOH is acidic due to formation of H 3 O + M O H + H 2 O H 3 O + + MO If electronegativities difference of M and O is less than that of H and O in H 2 O then MOH is basic due to formation of OH M O H + H O H [MOH 2 ] + + OH Stability of oxides decreases across a period. (Min. Max) Oxides of the following elements are amphoteric H, Be, Al, Ga, In, Tl, Sn, Pb, Sb, Bi, Po H 2 O is amphoteric (also called amphiprotic) H 2 O + H 2 O H 3 O + + OH Since it is H + acceptor (base) as well as H + donor (acid). BeO, Al 2 O 3, SnO 2, PbO 2,... are amphoteric since they form salts with acid as well as with base Al O 6HCl 2AlCl 2 3 base 3H Al O 2NaOH 3H O 2Na[Al(OH) ] 2 3 acid base oxide is acidic if it reacts with a base. oxide is basic if it reacts with an acid O 4

10 CCP 10 E X E R C I S E (PERIODICITY) 1. If Aufbau rule is not followed, K-19 will be placed in...block : s p d f 2. First, second and third I.P. values are 100 ev, 150 ev and 1500 ev. Element can be Be B F Na 3. Which has maximum ionisation potential? N O O + Na 4. N 0 /2 atoms of X(g) are converted into X + (g) by energy E 1.N 0 /2 atoms of X(g) are converted into X (g) by energy E 2. Hence ionisation potential and electron affinity of X (g) are 2E1 2(E1 E2), N N 0 2E N 0 1 2E, N ( E1 E N ) 2E, N none is correct statement 5. Which is maximum hydrated? NaCl MgCl 2 AlCl 3 SiCl 4 6. Which has maximum polarising power in cation? Li + Mg 2+ Al 3+ O 2 7. M(g) M + (g) + e, H = 100 ev M(g) M 2+ (g) + 2e, which is incorrect statement(s)? I 1 of M(g) is 100 ev I 1 of M+(g) is 150 ev I 2 of M(g) is 250 ev I 2 of M(g) is 150 ev 0 2 H = 250 ev 8. Which set has all the coloured ions Cu +, Cu 2+, Ni 2+ Cu 2+, Fe 2+, Co 2+ Cu 2+, Co 2+, Sc 3+ Na +, Mg 2+, Al Gd (64) has...electrons in f-electrones with sum of spin... 7, 3.5 8, 3 6, 3 none 10. Consider the isoelectronic ions : K +, S 2, Cl and Ca 2+ The radii of these ionic species follow the order Ca 2+ > K + > Cl > S 2 Cl > S 2 > K + > Ca 2+ S 2 > Cl > K + > Ca 2+ K + > Ca 2+ > S 2 > Cl 11. Astatine is the last element in halogen group (VII). It is expected to be more electronegative than iodine composed of diatomic molecules limited to an oxidation number of 1 in its compounds a solid at room temperature 12. The first ionisation potential (in ev) of N and O atoms are 14.6, , , , Atomic radii of F and Ne in Å are given 0.72, , , 0.72 none of these 14. Match List-I (Atomic number of elements) with list- II (Position of elements in periodic table) and select the correct answer using the codes given below the lists : List-I List-II A p-block B f-block C d-block D s-block A B C D Consider the following statements : 1. Cs + is more highly hydrated than the other alkali metal ions. 2. Among the alkali metals Li, Na, K and Rb, lithium has the highest melting point. 3. Among the alkali metals only lithium forms a stable nitride by direct combination Of these statements 1, 2 and 3 are correct

11 CCP 11 1 and 2 are correct 1 and 3 are correct 2 and 3 are correct 16. Match List I (Atomic number of the element) with List II (Position in the Periodic Table) and select the correct answer using the codes gives below the lists : List I List II A s-block B p-block C d-block D f-block Codes : A B C D The electronegativity difference between two elements A and B is 0.5. The magnitude of percent ionic character in single A B bond would be : An increase in both atomic and ionic radii with atomic number occurs in any group of the ionic radii of Ti(IV) and Zr(IV) ions are 0.68 Å and 0.74 Å respectively; but for Hf(IV) ion the ionic radius of 0.75Å which is almost the same as that for Zr(IV) ion. This is due to greater degree of covalency in compound of Hf 4+ lanthanide contraction difference in the co-ordination number of Zr 4+ and Hf 4+ in their compounds actinide contraction 19. Consider the following statements : For a given ionic concentration, the extent of ionpair formation is greater 1. the smaller the size of the ions. 2. the higher their valence 3. The higher the dielectric constant of the solvent. Of these statements 1 and 2 are correct 1 and 3 are correct 2 and 3 are correct 1, 2 and 3 are correct 20. The first ionization potentials of Na, Mg, Al and Si are such that Na < Mg < Al > Si Na < Al < Mg < Si Na > Mg > Al > Si Na < Mg < Al > Si 21. The electron affinities of N, O, S and Cl are such that N < O < S < Cl O < N < Cl < S O Cl < N S O < S < Cl < N 22. Fluorine has the highest electronegative among the ns 2 np 5 group on the Pauling scale but the electron affinity of fluorine is less than that of chlorine because the atomic number of fluorine is less then that of chlorine fluorine being the first member of the family behaves in an nusual manner chlorine can accommodate an electron better than fluorine by utilising its vacant 3d orbital small size, high electron density and an increased electron repulsion makes addition of an electron to fluorine less favourable than that in the case of chlorine. 23. The ionic radii of O 2, F, Na + and Mg 2+ are 1.35, 1.34, 0.95 and 0.66 Å respectively. The radius of the Ne atom is 1.39 Å 1.12 Å 0.85 Å 0.50 Å 24. The element which does not exist in liquid state at room temperature are Na Br Hg Ga 25. Which one of the following has the maximum number of unpaired electrons? Mg 2+ Ti 3+ V 3+ Fe The following acids have been arranged in the order of decreasing acid strength. Identify the correct order ClOH(I) BrOH(II) IOH(III) I > II > III II > I > III III > II > I I > III > II 27. The statement is not true for the long form of the periodic table it reflects the sequence of filling the electrons in the order of the sub-energy shells s, p, d and f

12 CCP 12 it helps to predict the stable valency states of the elements it reflects trends in physical and chemical properties of the elements. it helps to predict the relative inicity of the bond between any two elements. 28. The electronic configuration 1s 2, 2s 2, 2p 6, 3s 2, 3p 6, 3d 10, 4s 2, 4p 6, 4d 10, 5s 2 is for f-block element d-block element p-block element s-block element 29. Which of the following statements is false : elements of I-B and II-B groups are transition elements elements of V-B group do not contain metalloids elements of I-A and II-A groups are normal elements elements of IV-B group are neither strongly electronegative nor strongly electropositive 30. Transition metals are characterised by the properties : variable valency coloured compounds high melting and boiling points all of the above 31. The atomic number of an element is 16. This element in Periodic Table belongs to 32. Ionic radii of group VI and period II period III and group VI group IV and period II period III and IV Ti 4+ > Mn Cl < 37 Cl K + > Cl P 3+ < P Which of the following ions has the smallest radius? Ti 2+ Pt 2+ Ni 2+ Zr When the following five anions are arranged in order of decreasing ionic radius, the correct sequence is Se 2, I, Br, O 2, F I, Se 2, O 2, Br, F Se 2, I, Br, F, O 2 I, Se 2, Br, O 2, F 35. Which of the following ions has the largest heat of hydration? Na + Al 3+ F Sr Which of the following anions is most easily polarized? Cl Se 2 Br Te Of the four H values needed to calculate a lattice energy using the Born-Haber cycle, the one that is most difficult to measure is the heat of sublimation of the metal the heat of formation of gaseous atoms of the non-metal the ionization energy of the metal the electron affinity of the non-metal 38. The melting point of RbBr is C while that of NaF is C. The principal reason that the melting point of NaF is much higher than that of RbBr is that the molar mass of NaF is smaller than that of RbBr. the bond in RbBr has more covalent character than the bond in NaF the difference in electronegativity between Rb and Br is smaller than the difference between Na and F. the internuclear distance, r c + r a is greater for RbBr than for NaF. 39. Going down in a group from F to I, which of the following properties does not decreases ionic radius ionisation energy oxidising power electronegativity 40. Which of the following will have maximum electron affinity? 1s 2 2s 2 2p 5 1s 2 2s 2 2p 6 1s 2 2s 2 2p 6 3s 2 3p 5 1s 2 2s 2 2p 6 3s 2 3p Size of cation is smaller than that of the atom because of the whole of the outer shell of electrons removed increase in effective nuclear charge due to gain of electrons statement, that cation is smaller than atom, is wrong

13 CCP The sizes of the second and third row transition elements are almost the same. This is due to d- and f-orbitals do not shield the nuclei charge very effectively lanthanide contraction both true none is true 43. The factors that influence the ionisation energies are the size of the atom the charge on the nucleus how effectively the inner electron shell screen the nuclear charge all the above 44. Following are the values of the electron affinity of the formation of O and O 2 from O 142, , , , Covalency is favoured in the following cases a smaller cation a larger anion large charges on catio or anion all the above 46. A molecule H X will be 50% ionic electronegativity difference of H and X is 1.2 ev 1.4 ev 1.5 ev 1.7 ev 47. Representative elements belong to s- and p-block d-block d- and f-block f-block 48. Inert pair effect is shown by s-block p-block d-block f-block 49. Among the following stability of ions of Ge, Sn and Pb will be in order except Ge 2+ < Sn 2+ < Pb 2+ Ge 4+ > Sn 4+ > Pb 4+ Sn 4+ > Sn 2+ Pb 2+ < Pb Which is true statement Tl 3+ salts are better oxidising agents Ga + salts are better reducing agents Pb 4+ salts are better oxidising agents all of above 51. The first element of a group in many ways differs from the other heavier members of the group. This is due to the small size the high electronegativity the unavailability of d-orbitals all of above 52. Catenation properties of C, Si, Ge, Sn, Pb in order C >> Si > Ge Sn >> Pb C < Si < Ge < Sn < Pb C > Si > Sn > Ge > Pb none is correct 53. Melting points of NaCl, NaBr, NaI and NaF will be in order NaI < NaBr < NaCl < NaF NaF < NaCl < NaBr < NaI NaBr < NaF < NaCl < NaI NaCl < NaI < NaF < NaBr 54. Which is amphoteric oxides BeO SnO ZnO All 55. Atomic number 64 will have electronic configuration 1. c 2. a 3. c 4. b 5. d 6. c 7. c 8. b 9. d 10. c 11. d 12. a 13. a 14. b 15. d [Xe] 54 6s 2 4f 8 [Xe] 54 6s 2 4f 7 5d 1 [Xe] 54 4f 10 [Xe] 54 6s 2 4f 7 5p 1 A N S W E R S 16. a 17. a 18. b 19. b 20. b 21. a 22. c 23. a 24. a 25. d 26. a 27. d 28. b 29. d 30. d 31. b 32. a 33. c 34. d 35. b 36. d 37. d 38. d 39. a 40. c 41. b 42. a 43. d 44. b 45. d 46. d 47. a 48. b 49. d 50. d 51. d 52. a 53. a 54. d 55. b

14 CCP 14 TEST YOURSELF 1. Electron affinity is positive when O is formed from O O 2 is formed from O O + is formed from O electron affinity is always a negative value 2. Following triad has approximately equal size : Na +, Mg 2+, Al 3+ (iso-electronic) F, Ne, O 2 (sio-electronic) Fe, Co, Ni Mn +, Fe 2+, Cr (iso-electronic) 3. Stability order of + 3 and + 1 states of group IIIA (boron family) elements is Ga 3+ < In 3+ < Ti 3+ Ga + > In + > Tl + Ga + < In + < Tl + Ga 3+ < Ga + 4. If Aufbau and Hund s rule are not used, then K + would be coloured ion Na will be in same s-block (if these rules are true) both and are correct statements none 5. The first ionisation potential of Al is smaller than that of Mg because the atomic size of Al > Mg the atomic size of Al < Mg Al has one unpaired electron in p orbital the atomic number of Al > Mg 6. Fluorine does NOT form any polyhalide as other halogens because : it has maximum ionic character it has low F F bond energy (38.5 kcal mol 1 ) of the absence of d-orbitals in the valence shell of fluorine it beings about maximum coordination number in other elements 7. When an isotope undergoes K-capture, its mass number : remains the same while the atomic number increases by one remains the same while the atomic number increases by two remains the same while the atomic number decreases by one as well as the atomic number decreases by one 8. The electronegativities of N, C, Si and P are such that P < Si < C < N Si < P < N < C Si < P < C < N P < Si < N < C 9. The statement that is not correct for the periodic classification of elements is the properties of elements are the periodic functions of their atomic numbers non-metallic elements are lesser in number than metallic elements the first ionisation energies of elements along a period do not vary in a regular manner with increase in atomic number for transition elements the d-subshells are filled with electrons monotonically with increase in atomic number. 10. The correct order of increasing ionic character is BeCl 2 < MgCl 2 < CaCl 2 < BaCl 2 BeCl 2 < CaCl 2 < MgCl 2 < BaCl 2 BaCl 2 < CaCl 2 < MgCl 2 < BeCl 2 MgCl 2 < CaCl 2 < BeCl 2 < BaCl 2 1. b 2. c 3. c 4. b 5. c 6. c 7. c 8. c 9. d 10. a ANSWERS