Atom history
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- Democritus and Leucippus were ancient Greek philosophers who proposed the idea of atoms as indivisible and indestructible particles that all matter is composed of. They hypothesized that atoms come in different shapes and sizes and exist in empty space between them. - John Dalton further developed atomic theory in 1804, proposing that atoms of a given element are identical and have fixed properties, while atoms of different elements have different properties and combine in simple whole number ratios. - In the late 19th/early 20th century, experiments by Thomson, Rutherford, Bohr, Einstein, and Moseley revealed the internal structure of atoms, including the existence of electrons, photons, and that atoms have a
Atom history
- 2. X-Rays Nuclear energy Electricity & Radiations Nuclear Weapon Fighter Aircrafts Nuclear energy X-Rays & Radiations
- 3. • A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion • A modern thermonuclear weapon weighing little more than 2,400 pounds (1,100 kg) can produce an explosive force comparable to the detonation of more than 1.2 million tons (1.1 million tonnes) of TNT. Thus, even a small nuclear device no larger than traditional bombs can devastate an entire city by blast, fire and radiation. Nuclear weapons are considered weapons of mass destruction, and their use and control have been a major focus of international relations policy since their debut. • Only two nuclear weapons have been used in the course of warfare, both by the United States near the end of World War II. On 6 August 1945, a uranium gun-type device code-named "Little Boy" was detonated over the Japanese city of Hiroshima. Three days later, on 9 August, a plutonium implosion-type device code-named "Fat Man" was exploded over Nagasaki, Japan. These two bombings resulted in the deaths of approximately 200,000 Japanese people—mostly civilians—from acute injuries sustained from the explosions.
- 9. • Fighters were developed in World War I to deny enemy aircraft and dirigibles the ability to gather information by reconnaissance. Early fighters were very small and lightly armed by later standards, and most were biplanes built with a wooden frame, covered with fabric, and limited to about 100 mph. As control of the airspace over armies became increasingly important all of the major powers developed fighters to support their military operations. Between the wars, wood was largely replaced by steel tubing, which became aluminum tubing, and finally aluminum stressed skin structures began to predominate. • By World War II, most fighters were all-metal monoplanes armed with batteries of machine guns or cannons and some were capable of speeds approaching 400 mph. • Wings were made thinner and swept back to reduce trans-sonic drag which requiring new manufacturing methods to obtain sufficient strength. Skins were no longer sheet metal riveted to a structure, but milled from large slabs of alloy
- 17. Greek’s Concept of matter (460-370 B.C.) Matter is discontinuous. It is made up of Particles called Atoms. The properties of the atoms determine the properties of Matter.
- 18. Democritus & Leucippus • The story of the two Greeks Democritus and Leucippus. Democritus and Leucippus tear a piece of paper into smaller pieces until they cannot tear it anymore. And they call it atom.
- 19. Democritus & Leucippus • Atomic hypothesis The theory of Democritus and Leucippus held that everything is composed of "atoms", which are physically, but not geometrically, indivisible; that between atoms lies empty space; that atoms are indestructible; have always been, and always will be, in motion; that there are an infinite number of atoms, and kinds of atoms, which differ in shape, and size. Of the mass of atoms, Democritus said "The more any indivisible exceeds, the heavier it is." But his exact position on weight of atoms is disputed
- 20. Democritus & Leucippus • Is there an ultimate, indivisible unit of matter? In the 5th century BC, Leucippus and his pupil Democritus proposed that all matter was composed of small indivisible particles called atoms, in order to reconcile two conflicting schools of thought on the nature of reality. On one side was Heraclitus, who believed that the nature of all existence is change. On the other side was Parmenides, who believed instead that all change is illusion.
- 21. Democritus & Leucippus • With the work of Leucippus and Democritus ancient Greek philosophy reaches its zenith when the initial question of Thales after the true nature of matter culminated 180 years later in the subtle concept of atoms, which bears an amazing resemblance to the twentieth century's view of chemistry.
- 22. Democritus & Leucippus • The atomistic theory began as an endeavor to overcome the odd logical consequences of the Eleatic school. Leucippus and Democritus did not accept the Eleatic hypothesis that "everything is one" and that change and motion is an illusion. Parmenides had said the void is a fiction, because saying the void exists would mean to say there is something that is nothing, which he thought is a contradiction in itself, but he was deceived by thinking of "being" in the sense of "material being". Thinking of the void as real would have overthrown Parmenides' theory, because allowing the void to exist as "space bereft of body" (Aristotle) with adjoining plenums implies the opposite of classical monism.
- 23. Dalton’s Atomic Theory (1804) Atoms are indivisible & indestructible. They do not change during chemical reaction. Atoms of given element have exactly the same properties, but atoms of different elements have different properties.
- 24. Dalton’s Atomic Theory (1804) Five main points of Dalton's atomic theory • Elements are made of extremely small particles called atoms. • Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties. • Atoms cannot be subdivided, created, or destroyed. • Atoms of different elements combine in simple whole- number ratios to form chemical compounds. • In chemical reactions, atoms are combined, separated, or rearranged.
- 25. Dalton’s Atomic Theory (1804) Dalton proposed an additional "rule of greatest simplicity" that created controversy, since it could not be independently confirmed. When atoms combine in only one ratio, "..it must be presumed to be a binary one, unless some cause appear to the contrary".
- 26. Dalton’s Atomic Theory (1804) This was merely an assumption, derived from faith in the simplicity of nature. No evidence was then available to scientists to deduce how many atoms of each element combine to form compound molecules. In any case, Dalton's "rule of greatest simplicity" caused him to assume that the formula for water was OH and ammonia was NH, quite different from our modern understanding.
- 27. Dalton’s Atomic Theory (1804) Dalton's innovation was fully as important for the future of the science as Antoine Laurent Lavoisier's oxygen- based chemistry had been The law of conservation of mass The law of multiple proportions
- 30. Atoms
- 31. ATOM • The name atom comes from the Greek word (atomos, “indivisible”) from ἀ- (a-, “not”) and (temnō, “I cut”), which means uncuttable, or indivisible, something that cannot be divided further.
- 32. ATOM • The atom is a basic unit of matter that consists of a dense central nucleus surrounded by a cloud of negatively charged electrons. • A group of atoms can remain bound to each other, forming a molecule
- 33. ATOM • The concept of an atom as an indivisible component of matter was first proposed by early Indian and Greek philosophers. In the 17th and 18th centuries, chemists provided a physical basis for this idea by showing that certain substances could not be further broken down by chemical methods.
- 34. ATOM • The Development of the Atomic theory began with intuitive thought, when early Greek philosophers pondered of the nature of matter. • It took centuries to develop a complete picture of the pattern.
- 35. ATOM • During the late 19th and early 20th centuries, physicists discovered subatomic components and structure inside the atom, thereby demonstrating that the 'atom' was divisible. The principles of quantum mechanics were used to successfully model the atom.
- 36. ATOM • Atoms are minuscule objects with proportionately tiny masses. Atoms can only be observed individually using special instruments such as the scanning tunneling microscope. Over 99.94% of an atom's mass is concentrated in the nucleus, with protons and neutrons having roughly equal mass.
- 37. Cathode ray experiments (1879-1897) Cathode Rays are made up of Negative particles called Electrons. Electrons(─) are present in all kinds of matter. Protons are positive particles emanating from behind the cathode
- 38. Thomson’s Plum Pudding Model (1891) An atom is a positive ball of electricity with negative electrons embedded.
- 39. Albert Einstein Photon Theory of Light (1905) Light wave carries energy equal to h v, consist of quanta or corpuscles called photon.
- 40. Rutherford’s Gold Foil Experiment (1908-09) The atom is mostly empty space. Its mass is concentrated in the nucleus. (Nuclear Model) The Protons and neutrons are particles inside the nucleus.
- 41. Niels Bohr’s Atomic Model (1913) The atom is like solar system. Its mass is concentrated in the nucleus in circular orbits. Each electron has discrete amount of energy and does not lose any energy.
- 42. Moseley’s X ray experiments (1913) All atoms of one element have the same or fixed number of protons. The number of protons or atomic number is what identifies given element.
- 43. Moseley’s X ray experiments (1913) All atoms of one element have the same or fixed number of protons. The number of protons or atomic number is what identifies given element.
- 44. Moseley’s X ray experiments (1913) All atoms of one element have the same or fixed number of protons. The number of protons or atomic number is what identifies given element.
- 45. De Broglie’s Particle-wave concept of Electron(1924) The electron has both particle and wave properties