\n3. The atoms of an element are alike in all respect and differ from atoms of other elements.<\/td>\n | 3.\u00a0The atoms of an element may not be alike in all respects, as it is seen in the case of isotopes. Isotopes which are atoms of the same element having the same atomic number but different mass numbers.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Solution 2.<\/strong><\/span><\/p>\n(a) Inert elements: The elements which have complete outer most shell i.e. 2 or electrons. They ordinarily do not enter into any reaction.<\/p>\n (b) These exist as\u00a0monoatoms\u00a0because molecules of these elements contain only one atom.<\/p>\n (c)\u00a0Valence electrons:<\/strong>\u00a0The number of electrons present in the outermost shell or valence shell is known as valence electrons.<\/p>\nSolution 3.<\/strong><\/span><\/p>\nThe three isotopes of hydrogen differ only due to their mass number which is respectively 1,2 and 3 and named protium, deuterium and tritium. \n<\/p>\n Solution 4.<\/strong><\/span><\/p>\n\n\n\nAtomic number<\/strong><\/td>\nName with\u00a0valency<\/strong><\/td>\n<\/tr>\n\n4<\/td>\n | –<\/td>\n<\/tr>\n | \n15<\/td>\n | A solid non-metal of\u00a0valency\u00a03.<\/td>\n<\/tr>\n | \n8<\/td>\n | A gas of\u00a0valency\u00a02.<\/td>\n<\/tr>\n | \n19<\/td>\n | A metal of\u00a0valency\u00a01.<\/td>\n<\/tr>\n | \n14<\/td>\n | A non-metal of\u00a0valency\u00a04.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Solution 5.<\/strong><\/span><\/p>\n\n\n\nAtom<\/strong><\/td>\nAtomic number<\/strong><\/td>\nAtomic mass<\/strong><\/td>\nNo. of Protons<\/strong><\/td>\nNo. of Electrons<\/strong><\/td>\nNo. of Neutrons<\/strong><\/td>\nElectronic configuration<\/strong><\/td>\n<\/tr>\n\n(a) Sodium<\/td>\n | 11<\/td>\n | 23<\/td>\n | 11<\/td>\n | 11<\/td>\n | 12<\/td>\n | 2, 8, 1<\/td>\n<\/tr>\n | \n(b) Chlorine<\/td>\n | 17<\/td>\n | 35<\/td>\n | 17<\/td>\n | 17<\/td>\n | 18<\/td>\n | 2, 8, 7<\/td>\n<\/tr>\n | \n(c) Oxygen<\/td>\n | 8<\/td>\n | 16<\/td>\n | 8<\/td>\n | 8<\/td>\n | 8<\/td>\n | 2, 6<\/td>\n<\/tr>\n | \n(d) Carbon<\/td>\n | 6<\/td>\n | 12<\/td>\n | 6<\/td>\n | 6<\/td>\n | 6<\/td>\n | 2, 4<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n <\/p>\n Solution 6.<\/strong><\/span><\/p>\nThe significance of the number of protons found in the atoms in each of different element is fixed its place in periodic table.<\/p>\n Solution 7.<\/strong><\/span><\/p>\nAtomic numbers of –<\/p>\n \n\n\nX<\/strong><\/td>\nY<\/strong><\/td>\nZ<\/strong><\/td>\n<\/tr>\n\n6<\/strong><\/td>\n9<\/strong><\/td>\n12<\/strong><\/td>\n<\/tr>\n\n(2,4)<\/strong><\/td>\n(2,7)<\/strong><\/td>\n(2,8,2)<\/strong><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n (a) Y (2,7) forms Anion. \n(b) Z (2, 8,\u00a02) forms\u00a0Cation. \n(c) X (2,4) has four electrons in the valence shell.<\/p>\n Solution 8.<\/strong><\/span><\/p>\n(a) X+1 \n<\/sup>(b)\u00a0Oxidising\u00a0agent, because it has ability to donate electron.<\/p>\nSolution 9.<\/strong><\/span><\/p>\n(a) Mass number:<\/strong>The atomic mass number is defined as the sum of the number of protons and neutrons contained in the nucleus of an atom of that element. It is denoted by the\u00a0symbol A<\/strong>.<\/p>\n(b) Ion:<\/strong>\u00a0An atom or molecule that carries a positive or negative charge because of loss or gain of electrons.<\/p>\n(c)\u00a0Cation:<\/strong>\u00a0It is positively charged ion that is formed when an atom loses one or more electrons e.g. Na+<\/sup>, Hg2+<\/sup>, Ca2+<\/sup>\u00a0etc.<\/p>\n(d) Atom:<\/strong>\u00a0It is defined as the smallest unit of matter which takes part in a chemical reaction.<\/p>\n(e) Element<\/strong>: It is a substance which cannot be split up into two or simpler substances by usual chemical methods of applying heat, light or electric energy.\u00a0e.g. Hydrogen, Oxygen, Chlorine etc.<\/p>\n(f) Orbit:<\/strong>\u00a0It is defined as a circular path around the nucleus in which electrons of the atom revolve.<\/p>\nSolution 10.<\/strong><\/span><\/p>\nAtomic number = 2 Mass number = 4<\/p>\n Solution 11.<\/strong><\/span><\/p>\n(a)\u00a0(i) Atom E contains 7 protons. \n(ii) Atom E has an electronic configuration 2, 7. \n<\/strong><\/p>\n(b) Atom C Stands for\u00a07<\/sub>3<\/sup>Li \nAtom D stands for\u00a08<\/sub>16<\/sup>O \nCompound formula = Li2<\/sub>O<\/p>\n(c)\u00a0Metals are: A and C Non-metals are: E, D, E<\/p>\n Solution 12.<\/strong><\/span><\/p>\nNo of electrons in M Shell = 2 \nNumber of electrons in K and L shell will be 2, 8 and respectively. \nTherefore, Electronic configuration will be: 2, 8, 2. \nAtomic number = 2\u00a0+\u00a08\u00a0+\u00a02 =\u00a012<\/strong>,\u00a0Since, atomic number = Number of Protons \nNo of Protons =\u00a012<\/strong><\/p>\nSolution 13.<\/strong><\/span><\/p>\n \n(a) (ii)\u00a0<\/strong>Electronic configuration = 2, 8, 2 \n(b)\u00a0<\/strong>Mass numbers are different of two isotopes of magnesium because of different number of neutron, that is, 12 and 14 respectively.<\/p>\nSolution 14.<\/strong><\/span><\/p>\nNucleons:<\/strong>\u00a0Particles which constitute nucleus are called nucleons. Proton and neutrons are the nucleons. \nAt. weight of phosphorus = 31 Atomic number = 15 \nTotal number of nucleons = 31 (No. of P + No. of N)\u00a0No. of neutrons = 31 – 15 = 16 \nElectronic configuration \nNo. of electrons = 15 = 2,8,5 \n<\/p>\nSolution 15. \n<\/strong><\/span><\/p>\n(a)\u00a0<\/strong>Atoms of the same elements differing in the number of neutrons in their nuclei are known as isotopes. Thus, isotopes of an element have the same atomic number but different atomic mass number. \nThe fundamental\u00a0particles is\u00a0Neutrons which differs.<\/p>\nUses of isotopes:<\/strong><\/p>\n\n- Some isotopes are\u00a0Redioactive;\u00a0isotopes\u00a0of cobalt are used for treating cancer and other diseases.<\/li>\n
- An isotopes\u00a0of uranium\u00a0235<\/sup>U is used as a fuel in nuclear reactor.<\/li>\n<\/ol>\n
(b)<\/p>\n <\/p>\n Solution 16.<\/strong><\/span><\/p>\nIn chemical reactions only electrons take part. The chemical properties depend upon the electronic configuration.<\/p>\n The isotopes of element\u00a017<\/sub>35<\/sup>Cl and\u00a017<\/sub>37<\/sup>Cl have same atomic number and hence, the\u00a0same configuration. So they have same chemical properties. These differ only in physical contents and weights because neutrons contribute to the mass of an atom.<\/p>\n17<\/sub>35<\/sup>Cl and\u00a017<\/sub>37<\/sup>Cl have different number of neutrons 18 and 20 respectively.<\/p>\nSolution 17.<\/strong><\/span><\/p>\nThe atomic masses of the isotopes of chlorine are 35 and 37. However in any given sample of chlorine gas, the isotopes occur in approximate\u00a03 :\u00a01, 75% of Cl35<\/sup>, and 25% of Cl37<\/sup>. Therefore, the relative atomic mass or atomic weight of chlorine is 35.5.<\/p>\nFractional atomic weight of chlorine<\/p>\n <\/p>\n Solution 18.<\/strong><\/span><\/p>\n(a) Atomic number:<\/strong>\u00a0The number of protons present in the nucleus of an atom is the atomic number of that atom. It is represented by the\u00a0symbol Z<\/strong>. \nAtomic number (Z) = Number of protons (p)<\/strong><\/p>\n(b)<\/strong><\/p>\n\n\n\n<\/td>\n | No. of Protons<\/strong><\/td>\nNo. of Electrons<\/strong><\/td>\nNo. of Neutrons<\/strong><\/td>\nAtomic number<\/strong><\/td>\nMass\u00a0<\/strong>number<\/strong><\/td>\n<\/tr>\n\n35<\/sup><\/strong>\u00a0Cl \n<\/strong>17<\/sup><\/strong><\/td>\n17<\/td>\n | 17<\/td>\n | 18<\/td>\n | 17<\/td>\n | 35<\/td>\n<\/tr>\n | \n37<\/sup><\/strong>\u00a0Cl \n<\/strong>17<\/sup><\/strong><\/td>\n17<\/td>\n | 17<\/td>\n | 20<\/td>\n | 17<\/td>\n | 37<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n (c)\u00a0<\/strong>Electronic configuration of chlorine is 2, 8,\u00a07.<\/p>\nSolution 19.<\/strong><\/span><\/p>\n(a) Hydrogen \n(b) Element of zero group i.e. He (Helium) \n(c) Calcium (2, 8, 8, 2). Therefore, 2 electrons in valance shell. Hence\u00a0valency\u00a0is 2. \n(d) Chlorine atoms: 17<\/sub>35<\/sup>Cl and\u00a017<\/sub>37<\/sup>Cl \n(e) K shell.<\/p>\nSolution 20.<\/strong><\/span><\/p>\n(a)\u00a0<\/strong>Physical properties depend on the Atomic mass and isotopes have different mass number. (A) i.e. they have different number of neutrons. So, isotopes have different physical properties.<\/p>\n(b)\u00a0<\/strong>Argon does not react as, Argon has completely filled outer-most orbit. The atomic number of argon is 18. Therefore, electronic configuration is 2, 8,\u00a08. There are 8 electrons in the outermost or valance shell. Therefore, argon does not react.<\/p>\n(c)\u00a0<\/strong>Actual Atomic Mass is greater than mass number (P + N) since mass number is a whole number approximation of atomic mass unit. In fact Neutrons are slightly heavier than protons and atom includes the existence of over 200 sub-atomic particles.<\/p>\n(d)\u00a0<\/strong>17<\/sub>35<\/sup>Cl and\u00a017<\/sub>37<\/sup>Cl\u00a0are isotopes of chlorine element which differ in number of\u00a0neutrons. Whereas chemical properties are determined by electronic configuration\u00a0of an atom. Isotopes of an element are chemically alike.<\/p>\nSolution 21.<\/strong><\/span><\/p>\nElement A<\/strong><\/p>\nAtomic number = 7 \nElectronic configuration: = 2, 5 \nValency\u00a0of element A = 8-5 =\u00a0(3<\/strong>–<\/sup><\/strong>)<\/strong><\/p>\nElement B<\/strong><\/p>\nElectronic configuration 2,8,8\u00a0Valency\u00a0of element B =\u00a0 | | | | | | | |
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