Solution 8.<\/strong><\/span><\/p>\n(a) The properties that reappear at regular intervals, or in which there is a gradual variation at regular intervals, are called periodic properties and the phenomenon is known as the periodicity of elements.
\n(b) The third period elements, Na, Mg, Al, Si, P and Cl summarize the properties of their respective groups and are called typical elements.
\n(c) The elements of the second period show resemblance in properties with the elements of the next group of the third period leading to a diagonal relationship. Such elements are called bridge elements.<\/p>\n
Solution 9.<\/strong><\/span><\/p>\nBeryllium and magnesium will show similar chemical reactions as calcium. Since these elements belong to same group 2 and also have two electrons in their outermost shell like calcium.<\/p>\n
Solution 10.<\/strong><\/span><\/p>\n\n- Metals: Lithium, Beryllium, Sodium, Magnesium, Aluminium, Potassium, Calcium<\/li>\n
- Metalloids: Boron, Silicon<\/li>\n
- Non-metals: Hydrogen, Helium, Carbon, Nitrogen, Oxygen, Fluorine, Neon, Phosphorous, Sulphur, Chlorine, Argon<\/li>\n<\/ol>\n
Solution 11.<\/strong><\/span><\/p>\n(i) Properties: Non-metallic, highest\u00a0electronegativity<\/span>\u00a0in the respective periods, highest ionisation potentials in the respective periods, highest electron affinity in the respective periods
\n<\/span>\u00a0(ii) Salt-forming; hence, the common name is halogens.<\/span><\/p>\nSolution 12.<\/strong><\/span><\/p>\nThe main characteristic of the last element in each period of the periodic table is they are inert or chemically\u00a0unreactive.
\nThe general name of such elements is ‘Noble gases’.<\/p>\n
Solution 13.<\/strong><\/span><\/p>\nAccording to atomic structure, the number of valence electrons determines the first and the last element in a period.<\/p>\n
Solution 14.<\/strong><\/span><\/p>\n\n\n\nElements<\/strong><\/td>\nValency<\/strong><\/td>\nFormula of oxides<\/strong><\/td>\n<\/tr>\n\nNa<\/td>\n | 1<\/td>\n | Na2<\/sub>O<\/td>\n<\/tr>\n\nMg<\/td>\n | 2<\/td>\n | MgO<\/td>\n<\/tr>\n | \nAl<\/td>\n | 3<\/td>\n | Al2<\/sub>O3<\/sub><\/td>\n<\/tr>\n\nSi<\/td>\n | 4<\/td>\n | SiO2<\/sub><\/td>\n<\/tr>\n\nP<\/td>\n | 5<\/td>\n | P2<\/sub>O5<\/sub><\/td>\n<\/tr>\n\nS<\/td>\n | 2<\/td>\n | SO2<\/sub><\/td>\n<\/tr>\n\nCl<\/td>\n | 1<\/td>\n | Cl2<\/sub>O<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Solution 15.<\/strong><\/span><\/p>\n(i<\/span>) Noble gases \n(ii) Representative elements \n(iii) Transition elements \n(iv) Halogens \n(v) Alkaline Earth metals<\/p>\nSolution 16.<\/strong><\/span><\/p>\n(i<\/span>) 30 \n(ii) It belongs to group 12 and fourth period. \n(iii) It is a metal. \n(iv) The name assigned to this group is IIB.<\/p>\nSolution 17.<\/strong><\/span><\/p>\n(i) Electronic configuration of P: 2,8,5 \n(ii) 15th<\/sup>\u00a0Group and 3rd<\/sup>\u00a0Period. \n(iii) Valency of P = 8 – 5 = 3 \n(iv) Phosphorus is a non-metal. \n(v) It is an oxidizing agent. \n(vi) Formula with chlorine = PCl3<\/sub><\/p>\nExercise Intext 2<\/strong><\/span><\/p>\nSolution 1.<\/strong><\/span><\/p>\nAtomic size is the distance between the centre of the nucleus of an atom and its outermost shell. \nIt’s measured in Angstrom and Picometre.<\/p>\n Solution 2.<\/strong><\/span><\/p>\n(i) The atomic size of an atom increases when we go down a group from top to bottom. \n(ii) It increases as we move from right to left in a period.<\/p>\n Solution 3.<\/strong><\/span><\/p>\nSecond Period: Fluorine <Neon< Oxygen< Nitrogen < Carbon < Boron< Beryllium < Lithium. \nThird Period: Chlorine < Argon < Sulphur < Phosphorus < Silicon < Aluminum < Magnesium < Sodium.<\/p>\n Solution 4.<\/strong><\/span><\/p>\n(i) The size of Neon is bigger compared to fluorine because the outer shell of neon is complete(octet).As a result, the effect of nuclear pull over the valence shell electrons cannot be seen. Hence the size of Neon is greater than fluorine. \n(ii) Since atomic number of magnesium is more than sodium but the numbers of shells are same, the nuclear pull is more in case of Mg atom. Hence its size is smaller than sodium.<\/p>\n Solution 5.<\/strong><\/span><\/p>\n(i) An atom is always bigger than\u00a0cation\u00a0since\u00a0cation\u00a0is formed by the loss of electrons; hence protons are more than electrons in a\u00a0cation. So the electrons are strongly attracted by the nucleus and are pulled inward. \n(ii) An anion is bigger than an atom since it is formed by gain of electrons and so the\u00a0number of electrons are\u00a0more than protons. The effective positive charge in the nucleus is less, so less inward pull is experienced. Hence the size expands. \n(iii) Fe\u00a02+<\/sup>\u00a0is bigger than Fe3+\u00a0<\/sup>since Fe\u00a02+<\/sup>\u00a0has more number of electrons than Fe3+\u00a0<\/sup>and hence the inner pull by nucleus is less strong on it as compared to the pull on Fe3+<\/sup>.<\/p>\nSolution 6.<\/strong><\/span><\/p>\n\n- In increasing metallic character: F < O < N < C < B < Be < Li<\/li>\n
- In decreasing non-metallic character:\u00a0Cl\u00a0> S > P > Si > Al > Mg > Na<\/li>\n<\/ol>\n
Solution 7.<\/strong><\/span><\/p>\n(i) Across a period, the chemical reactivity of elements first decreases and then increases. \n(ii) Down the group, chemical reactivity increases as the tendency to lose electrons increases down the group.<\/p>\n Solution 7.<\/strong><\/span><\/p>\nThe periodic variation in electronic configuration as one move sequentially in increasing order of atomic number produces a periodic variation in properties. \nAs the elements are arranged in increasing order of atomic number, the metals with tendency to lose electrons are placed on the left and the metallic character decreases from left to right and increases down a group and non-metals with tendency to gain electrons are placed automatically on the right and the non-metallic character increase across a period and decreases down a group.<\/p>\n Solution 8.<\/strong><\/span><\/p>\n(i) The metallic character decreases as we go from left to right in a period. \n(ii) It increases as we go down a group.<\/p>\n Solution 9.<\/strong><\/span><\/p>\n(i) The element from the 17th<\/sup>\u00a0group has 7 electrons in its outermost shell. \n(ii) The name of the element is chlorine. \n(iii)\u00a0Chlorine belongs to the halogen family. \n(iv) The element has\u00a013<\/sub>Y27\u00a0<\/sup>three electrons in its outermost shell which it can donate; hence, its\u00a0valency\u00a0is three. While the\u00a0valency\u00a0of chlorine is 1. Thus,\u00a013<\/sub>Y27<\/sup>\u00a0which is Aluminium\u00a0can donate three electrons, and\u00a0chlorine can accept 1 electron to get the stable electronic configuration. \nTherefore, the formula of the compound is AlCl3<\/sub>.<\/p>\nSolution 10.<\/strong><\/span><\/p>\n(i) Yes, these elements belong to the same group but are not from the same period. \n(ii) We know that\u00a0m.p. decreases on going down the group. Hence, from the above table, the elements can be ordered according to their period as follows:<\/p>\n \n\n\nElements<\/strong><\/td>\nB<\/td>\n | C<\/td>\n | A<\/td>\n<\/tr>\n | \nm.p<\/strong>.<\/strong><\/td>\n180.0<\/td>\n | 97.0<\/td>\n | 63.0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n The metallic character increases as one\u00a0moves\u00a0down the group. \nHence, the order of the given elements with increasing metallic character is as follows: \nB<\/p>\n Solution 10.<\/strong><\/span><\/p>\nThe melting and boiling points of metals decrease on going down the group. \nExample: Observe the trend in group 1 elements given in the following table: \n<\/p>\n Solution 11.<\/strong><\/span><\/p>\nCorrect option: (ii) Potassium<\/p>\n Solution 12.<\/strong><\/span><\/p>\nCorrect option: (iii) I–<\/sup><\/p>\nSolution 13.<\/strong><\/span><\/p>\n(i)\u00a0\u00a0Barium will form ions most readily as the outermost valence electron which experiences the least force of attraction\u00a0by positively charged nucleus can be given away readily to form\u00a0cations<\/span>. \n(ii) All Group II elements have two valence electrons.<\/span><\/p>\nSolution 14.<\/strong><\/span><\/p>\n<\/p>\n Solution 15.<\/strong><\/span><\/p>\n\n- Group = 1<\/li>\n
- Period = 4<\/li>\n
- Valence electrons = 1<\/li>\n
- Valency\u00a0= 1<\/li>\n
- Metal<\/li>\n<\/ol>\n
Solution 16.<\/strong><\/span><\/p>\n(i)\u00a0It belongs to group II and has 2 valence electrons,\u00a0so it\u00a0is a metal. \n(ii)\u00a0Barium is placed below calcium in the group. Since the reactivity increases below the group, barium is more reactive than calcium. \n(iii)\u00a0It needs to lose 2 valence electrons to complete its octet configuration, so its valency is 2. \n(iv)\u00a0The formula of its phosphate will be Ba3\u00a0<\/sub>(PO4<\/sub>)2. \n(v)\u00a0As we move from left to right in a period, the size decreases, so it will be smaller than caesium.<\/p>\nSolution 17.<\/strong><\/span><\/p>\nSincethe size of the atom increases down the group, the ionic radii will also increase. Hence, the order of increasing atomic numbers in the group is Z < Y < X.<\/p>\n Solution 18.<\/strong><\/span><\/p>\n(i)\u00a0All groups do not contain both metals and non-metals. Group I and II contain only metals. \n(ii)\u00a0Atoms of elements in the same group have same number of valence electrons. They have same number of electrons present in their outermost shell. \n(iii)\u00a0The non-metallic character increases across a period with increase in atomic number. This is because across the period, the size of atom decreases and the valence shell electrons are held more tightly. \n(iv)\u00a0On moving from left to right in a period, the reactivity of elements first decreases and then increases, while in groups, chemical\u00a0reactivity of metals increases going down the group whereas reactivity of non-metals is decreases down the group.<\/p>\n Solution 19.<\/strong><\/span><\/p>\n(i)\u00a0A metal of valency one = 19 \n(ii)\u00a0A solid non-metal of period 3 = 15 \n(iii)\u00a0A rare gas = 2 \n(iv)\u00a0A gaseous element with valency 2 = 8 \n(v)\u00a0An element of group 2 = 4<\/p>\n Solution 20.<\/strong><\/span><\/p>\n(i) The properties of the elements are a periodic function of their\u00a0atomic number.<\/strong> \n(ii) Moving across a\u00a0period\u00a0of the periodic table, the elements show increasing\u00a0non-metallic<\/strong>\u00a0character. \n(iii) The elements at the bottom of a group would be expected to show\u00a0more\u00a0<\/strong>metallic character than the elements at the top \n(iv) The similarities in the properties of a group of elements are because they have the same\u00a0number of outer electrons.<\/strong><\/p>\nSolution 21(i).<\/strong><\/span><\/p>\nAn anion is formed by the gain of electrons. In the chloride ion, the number of electrons is more than the number of protons. The effective positive charge in the nucleus is less, so the less inward pull is experienced. Hence, the size expands. \n<\/p>\n Solution 21(ii).<\/strong><\/span><\/p>\nThe inert gas argon is the next element after chlorine in the third period.<\/p>\n In a period, the size of an atom decreases from left to right due to an increase in nuclear charge with an increase in the atomic number. However, the size of the atoms of inert gases is bigger than the previous atom of halogen in the respective period. This is because the outer shell of inert gases is complete. They have the maximum number of electrons in their outermost orbit; thus, electronic repulsions are\u00a0maximum. Hence, the size of the atom of an inert gas is bigger.<\/p>\n Solution 21(iii).<\/strong><\/span><\/p>\nIonisation potential of the element increases across a period because the atomic size decreases due to an increase in the nuclear charge, and thus, more energy is required to remove the electron(s).<\/p>\n Solution 21(iv).<\/strong><\/span><\/p>\nAlkali metals are strong reducing agents because they lose electrons easily to complete their octet.<\/p>\n Solution 22(i).<\/strong><\/span><\/p>\nNeon (Atomic number = 10) \nElectronic configuration = 1s2<\/sup>2s2<\/sup>2p6<\/sup><\/p>\nSolution 22(ii).<\/strong><\/span><\/p>\nElectronic configuration = 2, 8, 3 \nHence, atomic number = 13 \nThe element having atomic number 13 is Aluminium.<\/p>\n Solution 22(iii).<\/strong><\/span><\/p>\nThe element has a total of three shells; hence, the element belongs to the third period. \nFive valence electrons indicate that the element belongs to the fifth group (VA). \nHence, the element is phosphorus.<\/p>\n Solution 22(iv).<\/strong><\/span><\/p>\nThe element has a total of four shells; hence, the element belongs to the fourth period. \nTwo valence electrons indicate that the element belongs to the second group (IIA). \nHence, the element is calcium.<\/p>\n Solution 22(v).<\/strong><\/span><\/p>\nTwice as many electrons in its second shell as in its first shell indicates electronic configuration 1s2<\/sup>2s2<\/sup>. \nFrom the electronic configuration, the total number of electrons is 4. \nWe know that \nNumber of electrons = Number of protons = Atomic number \nThe element with atomic number 4 is beryllium.<\/p>\n | | | | | | | | | | | |