Atomic Structure and Periodic Table

1. Atomic Structure and Periodic Table

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. Part 1 : Atomic structure Historical background

4. The main deficiency in Dalton’s theory was that the atom was considered indivisible. It could not explain concepts like charge, electromagnetism, radiation etc. 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 John Dalton 1766 - 1844

5. Positive and negative plates generating electric field Glass tube filled with gas under low pressure Anode Cathodeë • Why should this happen? Was it because • the ray was made of light waves? • the raywas made of positive particles? • the raywas made of negative particles? High voltage source (10000V) Fluroscent screen The discovery of the internal structure of the atom: Cathode Ray Tube • 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 The scientist J.J.Thomson answered these questions

6. J.J.Thomson 1856 - 1940 Thomson’s atomic model • 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 ? • Thomson stated that • Cathode rays are a stream of particles (electrons) ; not light rays • Considering their deviation these particles must benegatively 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

7. Thin gold foil Alpha ray Polonium Alpha particle detector screen Box lined with Lead Rutherford’s experiment • Questions ! 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? • 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 1/50000cm • Out of approx. 20000 alpha particles • about 19990 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

8. Nucleus Electron 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 10-8cm while the radius of the nucleus is only 10-13 cm i.e 100000 times smaller than atomic radius. The scientist Niels Bohr further improved this model by stating that electrons can only occupy ‘allowed’ orbits whose energy levels are stable

9. 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 Progressive changes in the understanding of the atom

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

11. Symbol of the element A X Mass number Z 40 Ca 23 Na 1 H 20 11 1 Protons = ? Protons = ? Protons = ? Electrons = ? Electrons = ? Electrons = ? Neutrons = ? Neutrons = ? Neutrons = ? Inside the atomThe 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) The convention of indicating the atomic number and mass number of an element Atomic number

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 2n2 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. Nucleus 2S 2P 1S 3S Inside the atomOrbit, 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, pelliptical,dmore 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 Es < Ep < Ed < Ef … • 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)

14. Inside the atomOrbits, sub-orbits and the number of electrons

15. Inside the atomShapes of sub-orbits S sub-orbit p sub-orbit d sub-orbit

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

17. 1 H 1 1s 2s 2p 3s Inside the atomElectron configuration of elements - Hydrogen 1s1

18. 4 He 2 1s 2s 2p 3s Inside the atomElectron configuration of elements - Helium 1s2

19. 7 Li 3 1s 2s 2p 3s Inside the atomElectron configuration of elements - Lithium 1s2, 2s1

20. 9 Be 4 1s 2s 2p 3s Inside the atomElectron configuration of elements - Beryllium 1s2, 2s2

21. 11 B 5 1s 2s 2p 3s 6 5 Inside the atomElectron configuration of elements - Boron 1s2, 2s2, 2p1

22. 12 C 6 1s 2s 2p 3s 6 6 Inside the atomElectron configuration of elements - Carbon 1s2, 2s2, 2p2

23. 14 N 7 1s 2s 2p 3s 7 7 Inside the atomElectron configuration of elements- Nitrogen 1s2, 2s2, 2p3

24. 16 O 8 1s 2s 2p 3s 8 8 Inside the atomElectron configuration of elements- Oxygen 1s2, 2s2, 2p4

25. 19 F 9 1s 2s 2p 3s 10 9 Inside the atomElectron configuration of elements - Fluorine 1s2, 2s2, 2p5

26. 20 Ne 10 1s 2s 2p 3s 10 10 Inside the atomElectron configuration of elements - Neon 1s2, 2s2, 2p6

27. 1s 2s 2p 3s 3p 4s 3d 40 45 35 23 40 39 Ca K Na Cl Sc Ar 20 17 18 11 19 21 Inside the atomElectron configuration of elements–Sodium,Chlorine, Argon, Potassium, Calcium, Scandium . .

28. 1 2 3 Hydrogen H H H Deuterium Tritium 1 1 1 Inside the atomIsotopes • 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

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 2n2 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. Es < Ep < Ed < Ef …

30. 1 H :1s1 11 B :1s2, 2s2, 2p1 1 5 23 16 39 Na : 1s2, 2s2, 2p6, 3s1 K : 1s2, 2s2, 2p6,3s2, 3p6, 4s1 O : 1s2, 2s2, 2p4 8 11 19 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…

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. 1 18 2 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 3 4 5 6 7 Group Period Periodic table • Periodic table : Arrangement of elements according to their increasing atomic numbers • 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

33. 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 • Period 2 and 3 : Short periods • Each contains 8 elements • Period 4 and 5 : Long periods • Each contains 18 elements 18 1 2 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 3 4 5 6 7 Periodic tablePeriods

34. 18 1 • 1 electron in outermost orbit • Good reducing agents • React with water and release Hydrogen 2 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 3 4 5 6 7 Periodic tableAlkali metals (Group 1)

35. 18 1 • Two electrons in outermost orbit • Fairly good reducing agents • They release CO2 when their carbonate compounds are heated 2 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 3 4 5 6 7 Periodic tableAlkaline earth metals (Group 2)

36. 18 1 Other metals • Transition elements • Metallic properties reduce from left to right 2 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 3 4 5 6 7 Periodic tableTransition elements and other metals

37. Non-metals Metalloids Periodic tableNon-metals and metalloids 18 1 2 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 3 4 5 6 7

38. 18 1 • Halogens • 7 electrons in the outermost orbit • Good oxidising agents 2 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 3 4 5 6 7 Periodic tableHalogens (Group 17)

39. 18 1 • Outer orbits are fully filled with electrons • Chemically inactive 2 13 14 15 16 17 1 2 3 4 5 6 7 8 9 10 11 12 3 4 5 6 7 Periodic tableInert gases(group 18)

40. Periodic tableClassification according to external sub-orbit of atom P Blockû D Block f Block S Blockû 1 2 3 4 5 6 7

41. 3d 4s 3p 3s 2p 2s 1s Periodic tableElectron configuration Energy S block d block p block f block

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. The End