Atomic Structure PDF

CH M1 7 2 1 21 CH M1 7 2 1 22  Atomic Structure Atoms Atom consist of tiny nucleus (with diameter of about 10-13 cm) and electrons that moves about the nucleus at an average distance of about 10-8 cm from it. The radius of an atom is therefore a...

CH M1 7 2 1 21 CH M1 7 2 1 22  Atomic Structure Atoms Atom consist of tiny nucleus (with diameter of about 10-13 cm) and electrons that moves about the nucleus at an average distance of about 10-8 cm from it. The radius of an atom is therefore approximately 105 times larger than that of its nucleus 1.1 Constituation of the atom: The Nucleus:. The nucleus contains two kinds of fundamental particles: protons and neutrons. Protons are positively charged, neutrons have no charge. Electrons has a negative unit charge (1,60. 10 C ) -19. The number of protons in the nucleus is equal to the number of electrons outside the nucleus. An atom is completely specified by the formula X: is the chemical symbol of the element A: is the mass number Z: is the atomic number N : is the neutron number 24  Mass Number A ZX Element Symbol Atomic Number Complete the following table : Isotopes Isotopes : atoms with the same number of protons and different number of neutrons (same atomic number but different mass number) ISOTOPES Definition : Isotopes are atoms of the same element which contains the same number of protons but different number of neutrons Example What‛s the difrence between these two? In the nucleus, In the nucleus, thi s thi s one has 6 one has 6 protons protons and 6 and 7 neutrons. neutrons. 27  ISOBARS: Definition : Isobars are atoms of diferrents elements which contains the same mass numbers but different atomic number ISOTONES: Definition : Isotones are atoms of differrents elements which contains the same number of neutrons but different number of protons ISOELECTRONIC: Definition : Isoelectronic are atoms of differrents elements which contains the same number of electrons CH M1 7 2 1 29 30 CH M1 7 2 1 31  Electrical charge Mass Proton +1.602.10 -19 C 1,6726.1O -27 Kg =1836 me Neutron 0 1,6749.10 -27 Kg =1839me Electron -1,602.1O- 19 C 9,1094.10 -31 Kg 32 ATOMIC MASS Unit.Definition: It is the mass equal to one twelfth (1/12 ) of the mass of one atom of carbon -12 (C12) It called one a.m.u Votre texte ici Let‛s look for the mass of one atom of C ! We know that atoms of carbon weigh 12 gram. and 1 atom of carbon weigh than the a.m.u correspond to : 33 CH M1 7 2 1 34 Average Atomic Mass ‫اﻟﻛﺗﻠﺔ اﻟذرﯾﺔ اﻟﻣﺗوﺳطﺔ‬ (abandances of different isotopes of élément) there atomic mass There CH M1 7 2 1 35 CH M1 7 2 1 37 1- The électron revolves in circular orbits arround the nucleus only in certain energy states called stastionary states or energy levels (as the earth revolves around the sun) CH M1 7 2 1 39 2- Each orbit has a fixed energy and these these circular orbits are also known as energy levels. 3- Electrons in stable orbits or shell do not radiate 4 - Electrons can change orbits by - radiating (larger to smaller) - absorbing radiation (smaller to larger) 40  Bohr Radius The Bohr Radius (a0) is a physical constant, approximately aqual to the most probable distance between the nucleus and the electron in a hydrogen atom in its ground state (lowest-energy level). The value of Bohr Radius is5.2917721067x10-11 m or 0.53 Å Equation: n = principal quantum number of thé orbit h = Plank’s constant m = mass of électron e = charge of electron Z = Atomic number CH M1 7 2 1 41 Bohr Radius of Hydrogen Atom Orbit Radius n =1 r1≃ 0.53 Å n=2 r2 = 4 r1 = 2.116 Å n=3 r3 =9 r1 =4.761 Å n=4 r4 =16 r1 =8.464 Å n = infinity ∞ CH M1 7 2 1 42  Orbit Radius Orbit Radius n =1 r1= 0.53 Å n=1 0.2642 Å n=2 r2 = 4 r1 = 2.116 Å n =2 1.058 Å n=3 r3 =9 r1 =4.761 Å n =3 2.3805 Å n=4 r4 =16 r1 =8.464 Å n=4 4.232 Å n = infinity ∞ n = infinity ∞ CH M1 7 2 1 43 Equation: h= Plank’s constant = 6.63x10 -38Js 1 eV = 1,602 x 10 -19 J 1 m = 10 10Å CH M1 7 2 1 44  Energy of électron in H -atom E ionization 0 eV -_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_- n = ∞ Orbit Energy n =1 E1= -13.6 eV -0,85 eV n=4 -1,51 eV second excited state n=2 E2 =-3.4 eV n=3 n=3 E3 = -1.51eV n=4 E4 =- 0.85 eV -3,4 eV first excited state n=2 n = infinity 0 eV -13,6 eV’ ground state n=1 45 Différence between Excitation Energy and Ionisation Energy Of Hydrogen atom Excitation Energy Ionisation Energy It is the amount of energy required by an The energy required to Knock an electron electron to jump from the ground state n 1 Completely out of the atom to any one of the excited state n x From n1 to n∞ ΔE =E f -Ei 46  ΔE =E f -Ei n = ∞- - - - - - - - - - - - - - - - - - - - - - -0- * n=4 E4 =- 0.85 * ΔE= 0– (- 13,6) =13,6 eV n=3 E3 = -1.51 n=2 * E2 =-3.4 ΔE= -1,5 – (- 13,6) =12,1 eV ΔE= -3,4 – (- 13,6) =10,2 eV n=1 * * * E1= -13.6 CH M1 7 2 1 47 Absorption Emission E3 E3 λ E1 CH M1 7 2 1 48 Wave length Wave number CH M1 7 2 1 49