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Matter Classification Matter Metals Metallic Bonds Giant metallic strcuture Atoms Ions Molecules Periodic Table Ionic Bonds Covalent Bonds Ionic compounds Covalent compounds Giant ionic strcuture Giant covalent strcuture Simple molecular structure Semi-metals or Metalloids Non-metals van der Waals' forces Atoms Z is the atomic number A Z X = number of protons = number of electrons A is the mass number = no. of protons + no. of neutrons Atoms atomic number of Cl = 17 35 17 Cl = 17 protons = 17 electrons mass number = 35 = no. of protons + no. of neutrons = 17 + no. of neutrons no. of neutrons = 35 – 17 = 18 Electronic arrangement and electronic diagram 35 37 Electronic arrangement of or Cl 17 17 Cl = 2, 8, 7 Electronic diagram Cl Isotopes 35 17 Cl 37 17 Cl Isotopes are atoms of the same element with equal number of protons but different number of neutrons. OR Isotopes are atoms of the same element with equal atomic number but different mass number. Isotopes have similar chemical properties because they have the same number of outermost shell electrons. Isotopes have different physical properties because their atomic masses are different. Atomic mass The actual mass of one 35 = g 35 17 Cl atom 6.02 1023 It is meaningless to remember such value. Moreover, it is found that mass of an electron is just 1 of the 1840 mass of a proton. As a result, the mass of an atom is mainly due to mass of nucleus, i.e. total mass of protons and neutrons. Relative isotopic mass 12 Scientist assigned the mass of an C atom = 12.000 atomic mass unit (a.m.u.) Carbon-12 consists of 6 protons and 6 neutrons in the nucleus, 12 sub-atomic particles totally. As a result, relative mass of proton = relative mass of neutron = 1 a.m.u. Relative isotopic mass Relative isotopic mass = 1 12 mass of mass of isotope carbon 12 79 Relative isotopic mass of 35 Br = 79 a.m.u. (79 sub-atomic particles in the nucleus) Relative isotopic mass Elements contain isotopes and each isotope has its own abundance. Usually, we mention the names of reagents required in a reaction without specifying which isotopes. E.g. 23g of sodium burns in chlorine to form sodium chloride. What is the mass of chlorine gas required for the complete reaction? As a result, we have to find the weighted average of chlorine isotopes. Relative atomic mass Due to the presence of isotopes, atomic mass of an element should not be an integer. It should be the weighted means of the isotopes. Relative atomic mass = weighted average of the mass of 1 mass of 12 carbon 12 isotope Isotopes 35 17 Cl 37 17 Cl Relative abundance = 75% : 25% = 3 : 1 Relative atomic mass of Cl = 35 x 75% + 37 x 25% = 35.5 a.m.u. Isotopes 69 Ga 71 Ga If the relative atomic mass of Ga = 69.8, find the relative abundance of each isotope. 69 71 Ga Let the relative abundance of and Ga be x% and (100 – x)% respectively 69(x%) + 71(100-x)% = 69.8 x = 60 Isotopes Ga has two isotopes 69Ga and xGa . If the relative abundance of 69Ga is 60% and the relative atomic mass of Ga = 69.8. Find the value of x. 69(60%) + x(40)% = 69.8 x = 71