The document outlines the development of atomic structure theories from ancient Greek philosophers like Democritus and Aristotle to modern scientists in the 19th and 20th centuries like Dalton, Rutherford, Bohr, Chadwick and others. Key developments included evidence that atoms are made of even smaller particles like electrons and nuclei, discoveries of subatomic particles like protons and neutrons, and the emerging theories of quantum mechanics. This led to a new understanding of atoms and molecules at the quantum level in terms of electrons, isotopes, nuclear reactions and molecular geometry.

1. ATOMIC STRUCTURE PRESENTED BY: RENNALYN JOY L. DELOS SANTOS BSN-1B/F2

2. D E M O C R I T U S G R E E K E R A Suggested that the world was made of empty space and tiny, invisible particles called ATOMS. "by convention bitter, by convention sweet, but in reality atoms and void“

3. A R I S T O T L E G R E E K E R A Believed that matter was composed of 4 basic elements: WATER, FIRE, AIR and EARTH He was a well respected so everyone discounted his atomic theory and believed Aristotle’s theory without question.

4. 1800 1803 1832 1859 1869 1873 1874 1879 1886 1895 1896 1897 1898 1898 1900 ELEMENTS Dalton Faraday Plucker Mendeleev Maxwell Stoney Crookes Goldstein Roetgen Becquerel Thomson Rutherford Curie ATOMIC STRUCTURE

5. J O H N D A L T O N 1 8 0 3 He defined an atom as the smallest part of a substance that can participate in a chemical reaction. He proposed that elements are composed of identical atoms and that elements combine in definite proportions, STOICHIOMETRY . Dalton also produced an early table of atomic weights.

6. M I C H A E L F A R A D A Y 1 8 3 2 Studied the effect of electricity on solutions, coined term ELECTROLYSIS as a splitting of molecules with electricity, developed laws of electrolysis.

7. J U L I U S P L U C K E R 1 8 5 9 Built the first cathode ray tube, used for gas discharge..

8. D M I T R I M E N D E L E E V 1 8 6 9 He arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the PERIODIC LAW .

9. J A M E S C L E R K M A X W E L L 1 8 7 3 Maxwell’s equation demonstrated that electricity , magnetism and even light are manifestations of the same phenomenon : the ELECTRO MAGNETIC FIELD.

10. G E O R G E J O H N S T O N E S T O N E Y 1 8 7 4 Proposed that electricity was made of discrete negative particles he called ELECTRONS . He was also the first to propose a system of NATURAL UNITS for physical quantities.

11. S I R W I L L I A M C R O O K E S 1 8 7 9 Discovered cathode rays had the following properties: travel in straight lines from the cathode; cause glass to fluoresce ; impart a negative charge to objects they strike ; are deflected by electric fields and magnets to suggest a negative charge ; cause pinwheels in their path to spin indicating they have mass .

12. E U G E N E G O L D S T E I N 1 8 8 6 Used a Cathode ray tube to study CANAL RAYS which had electrical and magnetic properties opposite of an electron. He was an early investigator of discharge tubes . The discoverer of ANODE RAYS. Sometimes credited with the discovery of the PROTON.

13. W I L H E L M R O E T G E N 1 8 9 5 Using a Cathode ray tube, he observed that nearby chemicals glowed. Further experiments found very penetrating rays coming from the CRT that were not deflected by a magnetic field. He named them X-RAYS.

14. H E N R I B E C Q U E R E L 1 8 9 6 He discovered some chemicals spontaneously decompose and give off very penetrating rays.

15. J O S E P H J O H N T H O M S O N 1 8 9 7 He discovered the ELECTRON , the first subatomic particle. He also was the first to attempt to incorporate the electron into a structure for the atom. Studied "canal rays" and found they were associated with the proton H + .

16. R U T H E R F O R D 1 8 9 8 Studied radiations emitted from uranium and thorium and named them ALPHA and BETA.

17. M A R I E S K L O D O W S K A C U R I E 1 8 9 8 She and her husband Pierre also discovered the radioactive elements: POLONIUM and RADIUM . Provides the THEORY OF RADIOACTIVITY. Known for the techniques for isolating radioactive ISOTOPES .

18. ATOMIC STRUCTURE 1900 1900 1903 1904 1905 1906 1909 1911 1914 1916 1919 1920 Soddy; Planck Nagaoka Abegg Einstein Geiger Millikan Rutherford Moseley Lewis Aston ELECTRONIC STRUCTURE

19. S O D D Y 1 9 0 0 Observed spontaneous disintegration of radioactive elements into variants he called ISOTOPES or totally new elements. He also discovered HALF-LIFE , made initial calculations on energy released during decay.

20. M A X P L A N C K 1 9 0 0 He used the idea of quanta (discrete units of energy) to explain hot glowing matter. Founder of QUANTUM THEORY .

21. H A N T A R O N A G A O K A 1 9 0 3 Postulated a SATURNIAN MODEL of the atom with flat rings of electrons revolving around a positively charged particle.

22. R I C H A R D A B E G G 1 9 0 4 Discovered that inert gases had a stable electron configuration which lead to their chemical inactivity. Pioneer of valence Theory. Because of his research he proposed that the difference of the maximum positive and negative valence of an element tends to be eight. This has become to be called ABEGG’S RULE .

23. A L B E R T E I N S T E I N 1 9 0 5 Einstein showed that if light consisted of particle-like quantised photons, where the energy of the photon depended upon its wavelength, the photoelectric effect could be explained. This work led to a revolution in the understanding of both the electron and light. Light could behave as both a wave and a particle, depending upon the experiment.

24. H A N S G E I G E R 1 9 0 6 Co-inventor of the GEIGER COUNTER and for the GEIGER-MARSDEN EXPERIMENT which discovered the ATOMIC NUCLEUS.

25. R O B E R T A N D R E W S M I L L I K A N 1 9 0 9 He worked on an OIL-DROP EXPERIMENT (since repeated, with varying degrees of success, by generations of physics students) in which they measured the charge on a single ELECTRON .

26. E R N E S T R U T H E R F O R D 1 9 1 1 Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) GOLD FOIL METHOD . He established that the nucleus was: very dense, very small and positively charged. He also assumed that the electrons were located outside the nucleus.

27. H E N R Y M O S E L E Y 1 9 1 4 Using x-ray tubes, determined the charges on the nuclei of most atoms. He wrote that the “atomic number of an element is equal to the number of protons in the nucleus”. This work was used to reorganize the periodic table based upon atomic number instead of atomic mass.

28. G I L B E R T N E W T O N L E W I S 1 9 1 6 Lewis proposed 2 ELECTRON CHEMICAL BOND , later named the COVALENT BOND by Langmuir. He contributed to the study of thermodynamics, atomic structure, and bonding, as well as to the theory of acids and bases and the teaching of thermodynamics as applied to chemistry. His atomic model, known as the LEWIS – LANGMUIR OCTET and his distinction between ionic and covalent bonds marked great progress in understanding chemical bonding.

29. F R A N C I S W I L L I A M A S T O N 1 9 1 9 Discovered the existence of isotopes through the use of a mass spectrograph. He obtained definite evidence for the existence of two isotopes of the inert gas neon.

30. 1920 ELECTRONIC STRUCTURE 1922 1923 1927 1929 1930 Bohr Broglie Heisenberg Cockroft & Walton Schrodinger & Dirac ELECTRONIC STRUCTURE 1930 Chadwick & Pauling 1932 Hellman & Feynaman 1937 1938 Meitner, Hahn & Strassman 1940 MOLECULES

31. N I E L S B O H R 1 9 2 2 The BOHR MODEL or OLD QUANTUM THEORY of the atom, the theory that electrons travel in discrete orbits around the atom's His atomic model had atoms built up of successive orbital shells of electrons. The LIQUID DROP MODEL of the atomic nucleus. He identified the ISOTOPE OF URANIUM that was responsible for slow-neutron fission

32. L O U I S D E B R O G L I E 1 9 2 3 Discovered that electrons had a dual nature-similar to both particles and waves – PARTCLE/WAVE DUALITY.

33. W E R N E R H E I S E N B E R G 1 9 2 7 He is best known as a founder of QUANTUM MECHANICS , the new physics of the atomic world, and especially for the UNCERTAINTY PRINCIPLE in quantum theory. Proposed PRINCIPLE OF INDETERMINANCY- you can not know both the position and velocity of a particle.

34. C O C K R O F T & W A L T O N 1 9 2 9 They built an early linear accelerator and bombarded lithium with protons to produce ALPHA PARTICLES . Produced the first NUCLEAR REACTION using artificially accelerated particles, bombarding and disintegrating lithium nuclei with protons accelerated to several hundred keV.

35. E R W I N S C H R O D I N G E R 1 9 3 0 Viewed electrons as continuous clouds and introduced WAVE MECHANICS as a mathematical model of the atom. He made important contributions to the development of Quantum Mechanics.

36. P A U L D I R A C 1 9 3 0 Proposed ANTI-PARTICLES . [Anderson discovered the anti-electron (positron) in 1932 and Segre/Chamberlain detected the anti-proton in 1955.] Dirac made fundamental contributions to the early development of both QUANTUM MECHANICS and QUANTUM ELECTRODYNAMICS . He formulated the DIRAC EQUATION , which describes the behavior of FERMIONS and which led to the prediction of the existence of ANTIMATTER.

37. J A M E S C H A D W I C K 1 9 3 2 Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the NEUTRON . Chadwick proved the existence of neutrons, preparing the way towards the fission of Uranium 235 and the creation of the atomic bomb.

38. L I N U S P A U L I N G 1 9 3 2 Linus Pauling used empirical heat of reaction data to introduce the elemental property of electronegativity which he defined as: " The desire of an atom to attract electrons to itself ". Introduced ELECTRONEGATIVITY which defined the new atomic property as: " The power of an atom in a molecule to attract electrons to itself .“

39. H A N S H E L L M A N & R I C H A R D F E Y N M A N 1 9 3 7 - 3 9 The Hellmann-Feynman theorem states that once the spatial distribution of electrons has been determined by solving the Schrödinger equation, all the forces in the system can be calculated using classical electrostatics.

40. L I S E M E I T N E R, O T T O H A H N & S T R A S S M A N 1 9 3 8 Conducted experiments verifying that heavy elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction.

41. MOLECULES 1940 1941 1942 1943 Seaborg Fermi VSEPR

42. G L E N N S E A B O R G 1 9 4 1 - 5 1 Synthesized 6 transuranium elements and suggested a change in the layout of the periodic table. Dr. Seaborg and his colleagues are responsible for the identification of more than 100 isotopes of elements throughout the Periodic Table. He is also author of the actinide concept of heavy element electronic structure .

43. E N R I C O F E R M I 1 9 4 2 He conducted the first controlled chain reaction releasing energy from the atoms nucleus. The discovery of new radioactive elements produced by neutron irradiation, and for the discovery of nuclear reactions brought about by slow neutrons. FERMIUM , a synthetic element created in 1952 is named after him.

44. V S E P R 1 9 4 3 V ALENCE S HELL E LECTRON P AIR R EPULSION States that electron pairs (both bonded covalent electron pairs and non-bonded "lone-pairs" of electrons) repel each other. Is a super-simple technique for predicting the geometry of atomic centres in small molecules and molecular ions.