Modern Atomic theory
- 1. Copyrights Reserved Modern Atomic Theory & Atomic Structure By Prof. Dr. Muhammad.Attique.Khan Shahid
- 3. Copyrights Reserved In The Name Of ALLAHIn The Name Of ALLAH The Most Merciful & BenevolentThe Most Merciful & Benevolent Beyond ReckoningBeyond Reckoning
- 4. The Development of Atomic Theory
- 5. How did different scientists contribute to atomic theory?
- 6. The Greeks • Start of the idea of the atom • In 400 B.C the Greeks tried to understand matter and broke everything down into earth, wind, fire, and air. Fire Water Earth Air ~~ http://www.unit5.org/christjs/site%20map.htm
- 7. The Hellenic Market Fire Water Earth Air ~~ Blend these “elements” in different proportions to get all substances http://www.unit5.org/christjs/site%20map.htm
- 8. Origin of “Mother Earth” statement? http://www.unit5.org/christjs/site%20map.htm
- 9. Greek Model • Greek philosopher • “All matter is made up of tiny particles, invisible to the naked eye, that cannot be divided.” • He called the particles ‘atomos’ • No experiments to support his idea, which was, soon after, lost for about 2000 years. Democritu s “To understand the very large, we must understand the very small.” http://www.unit5.org/christjs/site%20map.htm
- 10. Democritus’s model of atom (no protons, electrons, or neutrons) Solid and INDESTRUCTABLE http://www.unit5.org/christjs/site%20map.htm
- 11. A ‘Model’… • is not a real thing, but is used to explain, mimic or simulate reality, • is used as a tool, • is used to predict what happens in the real world, • is changed or modified until it best fits new information, • may have some limitations or be valid only under certain conditions. Examples: globes, computer simulations, product prototypes
- 14. Copyrights Reserved Dalton’s Atomic Theory - 1808 • All matter is composed of atoms which cannot be subdivided • Atoms of same element are identical (size, mass, reactivity) • Atoms combine to form compounds in simple, whole # ratios • Chemical reactions involve the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction
- 15. Copyrights Reserved Dalton’s Theory • He deduced that all elements are composed of atoms. Atoms are indivisible and indestructible particles. • Atoms of the same element are exactly alike. • Atoms of different elements are different. • Compounds are formed by the joining of atoms of two or more elements.
- 16. Copyrights Reserved Thomson Model • He proposed a model of the atom that is sometimes called the “Plum Pudding” model. • Atoms were made from a positively charged substance with negatively charged electrons scattered about, like raisins in a pudding.
- 17. Copyrights Reserved Thompson • Discovered the electron • Determined the charge-to-mass ratio of an electron
- 18. Copyrights Reserved Cathode Ray Experiments • Any metal worked for anode • Negative electric field repelled beam • Object placed in path of glow blocked beam
- 19. Copyrights Reserved Evidence & Conclusions • cathode rays consisted of subatomic particles from atoms of anode • cathode rays are negatively charged • ∴ must also be positive charge • Millikan calculated electron’s mass to be 9.11 x 10-31 kg
- 20. Copyrights Reserved Thompson’s Atomic Model
- 21. Copyrights Reserved RUTHERFORD ATOMIC MODEL– Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all. – Some of the positively charged “bullets,” however, did bounce away from the gold sheet as if they had hit something solid. He knew that positive charges repel positive charges.
- 22. Copyrights Reserved The Gold Foil Experiment: Setup
- 23. Copyrights Reserved The Gold Foil Experiment: Hypothesis • The α-particles will pass straight through the atoms
- 24. Copyrights Reserved The Gold Foil Experiment: Outcome
- 26. Rutherford’s Model • Rutherford’s model describes an atomatom as mostly empty space, with a centeras mostly empty space, with a center nucleusnucleus that contains nearly all the mass – Like the pit in a peachpit in a peach
- 27. • The nucleus is tiny compared to the atom as a whole. • Image a marble is the nucleus. Place it on the 50 yard line in a stadium. Now place several electrons in random seats. The rest of the stadium/atom is empty!
- 28. Copyrights Reserved Rutherford’s Problems • How is nucleus held together? • Why don’t electrons collapse into nucleus? • H atom has 1 proton & He atom has 2 protons, ∴ mass ratio should be 2:1; instead the ratio is 4:1 …there must be another particle
- 29. Copyrights Reserved The Neutron • Discovered by James Chadwick in 1932. • Neutron is electrically neutral & has slightly greater mass than a proton Mystery solved.
- 30. Copyrights Reserved The Bohr Model
- 31. Copyrights Reserved Bohr Model • According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus.
- 32. Copyrights Reserved Emission Spectrums • When electricity is run through a sample of hydrogen gas, hydrogen atoms gain energy • H atoms loose that energy by emitting photons • Resulting spectrum is discontinuous continuous discontinuous
- 34. Energy Levels The energy that an electron has is based on its location around the nucleus. (Electrons that are closer to the nucleus have less energy than those that are farther away from the nucleus)
- 35. How can bookshelves help you understand the movement of electrons? •Each shelf represents an energy level •Each book represents an electron •You can move a book to a higher or lower shelf with the correct amount of energy. •A book cannot be between shelves (An electron can move by gaining or losing energy but can never be between energy levels)
- 36. Copyrights Reserved Bohr Model • Electrons move in circular orbits around the nucleus • Only certain energy levels are “permitted” (this explains the discrete lines for the emission spectrum of hydrogen)
- 37. Bohr’s Problems • Theory only explained behavior of Hydrogen’s electron • Violates Heisenberg’s Uncertainty principle- claimed to know exactly where an electron is and what it was doing.
- 38. Electron Orbital Notation • e- don’t actually zoom around the nucleus on little electron highways as seen in the Bohr Model of the Atom. • THEREFORE – true electron configuration isn’t that easy!
- 39. What are Quantum Numbers? Quantum number are a set of four values that define the energy state of an electron in an atom. Quantum number values are designated as n, l, m and s (s is often written as ms ) n is called the principal quantum number and ranges from 1, 2, 3, etc. (also refers to the energy level or shell l represents the orbital type and depends on n. It ranges from 0 through n – 1. It often called the azimuthal quantum number m depends on l. It ranges from – l thru 0 to + l. It defines the orbital orientation in space and is call the magnetic quantum number. S is the spin number and is either + ½ or – ½
- 40. Quantum numbers may be view as an electrons address. Just like your address, each has its own distinct set of values. For example in order to receive a letter, the address must contain state and zip, city, street and name. No other person has the exact same set of information. It is similar for electrons. They each have their own address, n, l, m, and s. NO TWO ELECTRON IN AN ATOM CAN HAVE THE EXACT SAME SET OF QUANTUM NUMBERS. QUANTUM NUMBERS ARE ASSIGNED TO EACH EACH ELECTRON USING THE RULES PREVIOUSLY STATED, STARTING FROM THE LOWEST VALUES. Assigning Quantum Numbers
- 41. Orbital types defined by the azimuthal quantum number l = 0 s type orbital l = 1 p type orbital l = 2 d type orbital One orientation Three orientations Five orientations l = 3 f type orbital Seven orientations (not shown)
- 42. Assigning Quantum Numbers to Atoms n l m satom H (1 e- ) 1 Lowest possible n value 0 Lowest possible l value (n – 1) 0 Lowest possible m value (-l > 0 > +l) -½ Lowest possible m value (- ½ or + ½ )
- 43. Assigning Quantum Numbers to Atoms n l m satom He (2 e- ) 1 0 0 -½ 1 0 0 +½ This time we can use the same n, l and m values as the first electron and still get a different set of values by changing s to = + ½ Energy level 1 is now complete. We are at the end of period (row) 1 on the Periodic Table.
- 45. This model is based upon Bohr’s model, except that electrons orbit the nucleus in random patterns. The region where these particles are found is referred to as the electron cloud. Electron Clouds Nucleus Next SlideNext Slide Current Model
- 46. Copyrights Reserved The Wave Model • Today’s atomic model is based on the principles of wave mechanics. • According to the theory of wave mechanics, electrons do not move about an atom in a definite path, like the planets around the sun.
- 47. Copyrights Reserved The Wave Model • In fact, it is impossible to determine the exact location of an electron. The probable location of an electron is based on how much energy the electron has. • According to the modern atomic model, at atom has a small positively charged nucleus surrounded by a large region in which there are enough electrons to make an atom neutral.
- 48. Copyrights Reserved Electron Cloud: • A space in which electrons are likely to be found. • Electrons whirl about the nucleus billions of times in one second • They are not moving around in random patterns. • Location of electrons depends upon how much energy the electron has.
- 49. Copyrights Reserved Electron Cloud: • Depending on their energy they are locked into a certain area in the cloud. • Electrons with the lowest energy are found in the energy level closest to the nucleus • Electrons with the highest energy are found in the outermost energy levels, farther from the nucleus.
- 50. Copyrights Reserved Indivisib le Electron Nucleus Orbit Electron Cloud Greek X Dalton X Thomson X Rutherfor d X X Bohr X X X Wave X X X
- 52. Copyrights Reserved Modern View of Dalton’s Atomic Theory 3 major differences between modern atomic theory & Dalton’s atomic theory: • Atoms are NOT indivisible – they are made up of protons, neutrons, and electrons • Atoms of the same element are NOT exactly alike – they can have different masses (isotopes) • Atoms CAN be changed from one element to another, but not by chemical reactions (nuclear reactions)
- 53. Copyrights Reserved Atomic Structure & Isotopes
- 54. Atoms of the same element are no necessarily alike . . . Same atomic number different mass number
- 55. Isotopes… Are atoms that have the same number of protons, but a different number of neutrons.
- 56. Copyrights Reserved Isotopes • All atoms in an element have the same atomic number • However, 2 atoms of the same element can have different mass numbers – called isotopes • Isotopes have: – Same # of p+ – Different # of no
- 57. Copyrights Reserved Some Common Isotopes H H H 1 1 2 1 3 1 C C C 12 6 13 6 14 6 U U 235 92 238 92
- 59. Copyrights Reserved Mass Spectrometry • Technique used to determine atomic mass e- Atom bombarded by stream of high energy electrons e- e- collides with atom, “bounces” off, but transfers some energy to it e- + Atom dissipates excess energy by expelling an electron
- 60. Copyrights Reserved Mass Spectrometry, cont. • Ions are accelerated through a magnetic field • Amount of deflection depends on the ion’s mass • Highest mass deflected least • Lowest mass deflected most N S + + + + ++++
- 61. Copyrights Reserved Mass Spectrometry, cont. Mass (amu) Sample mass spec for chlorine Relative abundance of each isotope can be determined from relative peak heights 35 37
- 62. Copyrights Reserved Relative Abundance & Atomic Mass • Relative isotopic abundance is then used to calculate atomic mass • Atomic mass is the weighted average of the mixture of isotopes
- 63. Copyrights Reserved Example average atomic mass = (atomic mass 35 Cl)(fraction 35 Cl) + (atomic mass 37 Cl)(fraction 37 Cl) = (34.968 amu)(0.7577) + (36.965 amu) (0.2423) = 35.45 amu Calculate the atomic mass of Cl given the relative abundances of its isotopes: 35Cl – 75.77% 37Cl – 24.23%
- 64. Einstein • 1879-1955 • The End
- 65. Do Theories in Science Stay the Same? • Ideas and theories in Science change as new iinformations gathered. Our theory about the atom has changed over time as new studies are done. Even though no one has ever seen an atom up close we are still able to make new discoveries – just like we have made new discoveries about dinosaurs.
- 66. The FUTURE Since atomic theory is just a theory, we will continue to challenge it and hopefully find more new and exciting things in our atom
- 67. The FUTURE Since atomic theory is just a theory, we will continue to challenge it and hopefully find more new and exciting things in our atom
Editor's Notes
- #8: Original concept of element: Four element theory AIRcombined to form all other materials by combining WATERin different proportions. EARTH AIR
- #10: Atomists; they argued for a completely materialistic universe consisting of atoms moving in a void. Since mere fragments of the ideas of Leucippus are known, his pupil, Democritus of Abdera (c 460 -370 B.C.) is considered the elaborator of this concept. Aaron J. Ihde The Development of Modern Chemistry, Dover Publishing, 1984 pg 6 It should also be noted that the Romans were not a scientific people and made almost no scientific contributions of their own. “To understand the very large, we must understand the very small.” -Democritus