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1 Atomic Structure and Periodic Table. 2 What are we going to learn ? Part 1: Atomic structure Historical background Dalton Thomson Rutherford/ Bohr Inside.

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Presentation on theme: "1 Atomic Structure and Periodic Table. 2 What are we going to learn ? Part 1: Atomic structure Historical background Dalton Thomson Rutherford/ Bohr Inside."— Presentation transcript:

1 1 Atomic Structure and Periodic Table

2 2 What are we going to learn ? Part 1: Atomic structure Historical background Dalton Thomson Rutherford/ Bohr Inside the atom Orbits and sub-orbits Atomic number and Atomic mass Electron configuration of elements Part 2: Periodic Table

3 3 Part 1 : Atomic structure Historical background

4 4 Dalton’s atomic theory John Dalton, English scientist Matter is made up of atoms All atoms of an element have the same mass and the same properties Atoms are indestructible Atoms combine to form compounds The main deficiency in Dalton’s theory was that the atom was considered indivisible. It could not explain concepts like charge, electromagnetism, radiation etc. John Dalton

5 5 Fluroscent screen Glass tube filled with gas under low pressure Positive and negative plates generating electric field High voltage source (10000 V) Cathode ë Anode The discovery of the internal structure of the atom: Cathode Ray Tube The scientist J.J.Thomson answered these questions Experiments using electric discharge tube and cathode ray tube helped in discovering the internal structure of an atom It was observed that the ray emanating from the cathode would deviate under the influence of electric field between the positive and negative plates Why should this happen? Was it because  the ray was made of light waves?  the ray was made of positive particles?  the ray was made of negative particles?

6 6 Thomson stated that Cathode rays are a stream of particles (electrons) ; not light rays Considering their deviation these particles must be negatively charged. Thomson’s atomic model Atoms are positively charged spheres Electrons are microscopic constituents of atoms Negatively charged electrons are embedded in the atom like seeds of a water melon The scientist Ernest Rutherford answered these questions J.J.Thomson But more doubts emerged !  How do we know that the atom is solid ?  How are positive charges distributed in the atom ?  Why are electrons the only particles coming out of atoms ?

7 7 Rutherford’s experiment Thin gold foil Polonium Alpha particle detector screen Box lined with Lead Alpha ray Rutherford fired alpha particles at high velocity on a thin gold foil Alpha particles: Minute positively charged particles. Their source : Polonium Thickness of gold foil 1 / cm Out of approx alpha particles about passed through the foil without deviation ; nine particles were scattered in various directions; only one particle took a U turn and deviated by almost 180 degrees Questions !  If the atom was solid would most alpha particles have gone through the foil without deviating ?  If positive particles were distributed uniformly inside the atom would only nine alpha particles have been scattered ?  Only one alpha particle seems to have collided against a solid part of the atom and come right back. Would this solid part be smaller or larger compared to the size of the atom?

8 8 Rutherford’s planetary model of the atom The mass and positive charge of an atom are concentrated in the centre (called as nucleus) Negatively charged electrons revolve around the nucleus in circular or elliptical orbits just like the planets which orbit around the sun The atom is largely hollow Atomic radius is cm while the radius of the nucleus is only cm i.e times smaller than atomic radius. Nucleus Electron The scientist Niels Bohr further improved this model by stating that electrons can only occupy ‘allowed’ orbits whose energy levels are stable

9 9 Progressive changes in the understanding of the atom Dalton (1808) The smallest indivisible particle of an element Thomson (1897) negatively charged electrons embedded in a positively charged solid sphere Rutherford (1911) Planetary model. Negatively charged electrons orbiting around extremely small positively charged solid nucleus Bohr (1913) Electrons can occupy only ‘allowed’ orbits having stable energy levels

10 10 Inside the atom Part 1: Atomic structure (contd)

11 11 Inside the atom The fundamental particles The nucleus contains Z number of positively charged protons Z is called the atomic number The nucleus contains N number of chargeless neutrons A = Z + N is called the atomic mass number Negatively charged electrons rotate around the nucleus in orbits (or shells) X A Z Mass number Atomic number Symbol of the element H 1 1 Protons = ? Electrons = ? Neutrons = ? Ca Na The convention of indicating the atomic number and mass number of an element Protons = ? Electrons = ? Neutrons = ? Protons = ? Electrons = ? Neutrons = ?

12 12 Inside the atom Fundamental particles The attraction between positively charged nucleus and negatively charged electrons keeps the electrons within the atom An orbit with orbit number ‘n’ can contain maximum 2 n 2 electrons In neutral atoms the number of protons is equal to the number of electrons Protons and neutrons have the same mass ( 1.6 x 10 –24 gm ) The mass of an electron is 1837 times less than that of a proton The chemical properties of an element depend upon the electrons in the outermost orbit

13 13 Inside the atom Orbit, sub-orbit and energy levels Electrons can orbit around the nucleus only in ‘allowed’ orbits These orbits contain circular and elliptical sub-orbits Sub-orbits are named as : s, p, d, f, g… s circular, p elliptical, d more elliptical,… The energy level of elliptical sub-orbits is greater than that of the circular sub-orbit In every orbit, electrons in s sub-orbit have the least energy level, electrons in p sub-orbit have a little more energy and so on E s < E p < E d < E f … The number of sub-orbits in an orbit are equal to the number of the orbit First orbit has 1 sub-orbit (called s) Second orbit has 2 sub-orbits ( s, p) Third orbit has 3 sub-orbits ( s, p, d) 3S 2P 2S Nucleus 1S

14 14 Inside the atom Orbits, sub-orbits and the number of electrons Orbit No.Number of sub-orbits Names of sub-orbits Maximum Number of electrons in the sub-orbits Maximum number of electrons in the orbits 111s22 222s 2p s 3p 3d s 4p 4d 4f

15 15 Inside the atom Shapes of sub-orbits S sub-orbitp sub-orbit d sub-orbit

16 16 Inside the atom Electron configuration of elements Rules 1.S sub-orbit: max 2 electrons, p sub-orbit: max 6, d sub-orbit: max 10… 2.The sub-orbit with the least energy ‘1s’ is filled first å 3.Thereafter electrons occupy the remaining sub-orbits in the order of increasing energy levels 4.The order of increasing energy is as shown 5s 4s 3s 2s 1s 2p 3p 4p 3d 4d Energy Shouldn’t 3d have come after 3p? Is there something wrong?

17 17 Inside the atom Electron configuration of elements - Hydrogen 1s2s2p3s H 1 1 1s 1

18 18 Inside the atom Electron configuration of elements - Helium 1s2s2p3s He 2 4 1s 2

19 19 Inside the atom Electron configuration of elements - Lithium Li 3 7 1s2s2p3s 1s 2, 2s 1

20 20 Inside the atom Electron configuration of elements - Beryllium 1s2s2p3s Be 4 9 1s 2, 2s 2

21 21 Inside the atom Electron configuration of elements - Boron B s2s2p3s 6 5 1s 2, 2s 2, 2p 1

22 22 Inside the atom Electron configuration of elements - Carbon C s2s2p3s 6 6 1s 2, 2s 2, 2p 2

23 23 Inside the atom Electron configuration of elements- Nitrogen N s2s2p3s 7 7 1s 2, 2s 2, 2p 3

24 24 Inside the atom Electron configuration of elements- Oxygen O s2s2p3s 8 8 1s 2, 2s 2, 2p 4

25 25 Inside the atom Electron configuration of elements - Fluorine F s2s2p3s s 2, 2s 2, 2p 5

26 26 Inside the atom Electron configuration of elements - Neon Ne s2s2p3s 1s 2, 2s 2, 2p 6 10

27 27 Inside the atom Electron configuration of elements – Sodium,Chlorine, Argon, Potassium, Calcium, Scandium Na s2s2p3s3p4s3d Cl Ar K Ca Sc

28 28 Inside the atom Isotopes Isotopes : Atoms of an element with the same atomic number but different mass number In other words the number of protons is equal but the number of neutrons varies H 1 1 Hydrogen H 2 1 Deuterium H 3 1 T ritium

29 29 Atomic structure What have we learnt ? The nucleus contains positively charged protons and chargeless neutrons Protons and neutrons have equal mass Atomic number Z = Number of protons in the nucleus Mass Number A = Number of protons + neutrons Negatively charged electrons rotate around the nucleus in ‘allowed’ orbits with stable energy levels In neutral atoms the number of electrons and protons is equal The mass of an electron is 1837 times less than that of a proton The n th orbit can contain maximum 2n 2 electrons Orbits contain circular ( s) and elliptical ( p, d, f, g…) sub-orbits The n th orbit contains n sub-orbits Energy level of elliptical sub-orbits is more than that of circular sub-orbits s sub-orbit has the least energy ; p sub-orbit has a little more and so on. E s < E p < E d < E f …

30 30 Atomic structure What have we learnt ? Electron configuration of elements As atomic number increases electrons in atoms occupy various orbits/- sub-orbits Rules of electron configuration Max 2 electrons in s sub-orbit, max 6 in p sub-orbit and so on 1s, the sub-orbit with the least energy level, is filled first Thereafter remaining sub-orbits are filled in the order of increasing energy level The order of sub-orbits with increasing energy levels is : 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p… H : 1s B : 1s 2, 2s 2, 2p O : 1s 2, 2s 2, 2p Na : 1s 2, 2s 2, 2p 6, 3s K : 1s 2, 2s 2, 2p 6, 3s 2, 3p 6, 4s

31 31 Part 2 Periodic table Based on our knowledge of electron configuration of elements we shall see how the elements can be logically ordered

32 32 Periodic table Periods : Seven rows In each period the chemical properties of elements change progressively from left to right Group : Eighteen columns Properties of elements in the same group have some similarities Periodic table : Arrangement of elements according to their increasing atomic numbers Period Group

33 33 Periodic table Periods Period 2 and 3 : Short periods Each contains 8 elements Period 4 and 5 : Long periods Each contains 18 elements Period 6 : Extra long period 32 elements After Lanthanum (La) fourteen elements are shown separately at the bottom Period 7 : 32 elements Many of these elements are man- made and short-lived After Actinide (Ac) 14 elements are shown separately at the bottom

34 34 Periodic table Alkali metals (Group 1) electron in outermost orbit Good reducing agents React with water and release Hydrogen

35 35 Periodic table Alkaline earth metals (Group 2) Two electrons in outermost orbit Fairly good reducing agents They release CO 2 when their carbonate compounds are heated

36 36 Periodic table Transition elements and other metals Transition elements Metallic properties reduce from left to right Other metals

37 37 Periodic table Non-metals and metalloids Metalloids Non-metals

38 38 Periodic table Halogens (Group 17) Halogens 7 electrons in the outermost orbit Good oxidising agents

39 39 Periodic table Inert gases ( group 18) Outer orbits are fully filled with electrons Chemically inactive

40 40 Periodic table Classification according to external sub-orbit of atom 1 H 2 He 3 Li 4 Be 5B5B 6C6C 7N7N 8O8O 9F9F 10 Ne 11 Na 12 Mg 13 Al 14 Si 15 P 16 S 17 Cl 18 Ar 19 K 20 Ca 21 Sc 22 Ti 23 V 24 Cr 25 Mn 26 Fe 27 Co 28 Ni 29 Cu 30 Zn 31 Ga 32 Ge 33 As 34 Se 35 Br 36 Kr 37 Rb 38 Sr 39 Y 40 Zr 41 Nb 42 Mo 43 Tc 44 Ru 45 Rh 46 Pd 47 Ag 48 Cd 49 In 50 Sn 51 Sb 52 Te 53 I 54 Xe 55 Cs 56 Ba Hf 73 Ta 74 W 75 Re 76 Os 77 Ir 78 Pt 79 Au 80 Hg 81 Tl 82 Pb 83 Bi 84 Po 85 At 86 Rn 87 Fr 88 Ra Rf 105 Db 106 Sg 107 Bh 108 Hs 109 Mt 110 Uun 111 Uuu 112 Uub 113 Uut 114 Uuq 115 Uup 116 Uuh 117 Uus 118 Uuo 57 La 58 Ce 59 Pr 60 Nd 61 Pm 62 Sm 63 Eu 64 Gd 65 Tb 66 Dy 67 Ho 68 Er 69 Tm 70 Yb 71 Lu 89 Ac 90 Th 91 Pa 92 U 93 Np 94 Pu 95 Am 96 Cm 97 Bk 98 Cf 99 Es 100 Fm 101 Md 102 No 103 Lr S Block û D Block P Block û f Block

41 41 4s 3s 2s 1s 2p 3p 3d Energy H He Li Be B C N O F Ne Na MgAl Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe CsBa Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn Fr Ra La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Ac Th Pa U Periodic table Electron configuration S block d blockp block f block

42 42 Periodic table: What have we learnt ? Periodic table : Arrangement of elements in the order of their atomic number Contains 18 columns (called ‘Groups’) and 7 rows (called ‘Periods’) Elements in the same group have similar chemical properties First group: Alkali metals (Good reducing agents) Second group: Alkaline earth metals (Fairly good reducing agent) Seventeenth group: Halogens (Good oxidising agents) Eighteenth group : Inert gases In a period, as you go from left to right, metallic properties reduce while non-metallic properties increase å Second and third period : Short periods (8 elements) Fourth and fifth periods : Long periods (18 elements) Sixth and seventh period : Extra long period (32 elements)

43 43 The End


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