Presentation on theme: "Main Menu Great Pyramids 2900 BCE Atomic Theory Founders of"— Presentation transcript:
1Main Menu Great Pyramids 2900 BCE Atomic Theory Founders of Law of Conservation of Mass1785Atomic Theory of Matter1803Law of DefiniteProportions1797RadioactivityValue of Pi240 BCEAlgebra820Admission chargedfor a concert1672Civil War1st McDonald’s1955440 BCEMain Menu
2Leucippus and Democritus Leucippus of Miletus (circa B.C.E.) originated the concept of the atomDemocritus of Abdera (circa 460 –371 B.C.E.) was a pupil of Leucippus.Atomic TheoryMatter is made up of indivisible particles called atoms- atom comes from the Greek “atomos” meaning uncuttableAtoms are completely solid with no internal structureAtoms differ in size, shape and weight
3Total mass of Reactants Antoine LavoisierBorn 1743 – Died 1794French ChemistLaw of Conservation of MassFirst modern chemical textbookLaw of Conservation of MassIn a chemical reaction, mass is neither created nor destroyedTotal mass of ReactantsTotal mass of Products=
4Joseph Proust Born 1754 – Died 1826 French Chemist 1797 Law of Definite Proportions (also known as Law of Constant Composition)Law of Definite ProportionsShowed that copper carbonate must always be composed of the same fixed proportions of copper, carbon and oxygen.Generalized that the elements in all compounds are present in fixed proportions by weight.
5John Dalton Born 1766 - Died 1944 British Chemist and Physicist Developed the atomic theory of matterDalton’s Atomic TheoryEach element is composed of extremely small particles called atomsAll atoms of a particular element are identical, atoms of different elements have different propertiesAtoms are neither created nor destroyed in a chemical reactionCompounds contain atoms of two or more elements
6Wilhelm Roentgen Born 1845 – Died 1923 German Physicist Awarded Nobel Prize in 1901 for the discovery of the X-rays1895 – discovered X-rays (called them Roentgen’s rays)While experimenting with a Crookes tube, he discovered a new type of ray emitted from the tube which would cast shadows of solid objectsThese rays pass through most substances, including the soft tissue of the body, and leave bones and solid metals visible
7Antoine-Henri Becquerel Born 1852 – Died 1908French Scientist1896 – discovered radioactivity as a spontaneous emission of radiation by a material and called the emissions becquerel rays.Observed the image of uranium crystals on photographic plates.Showed that this radiation differed from X-rays because it could be deflected by a magnetic field and therefore must contain charged particles.
8Marie Curie Pierre Curie Born 1867 – Died 1934 1898 – observed that thorium compounds also emit becquerel rays.Invented the word “radioactivity” to describe this behavior.Pierre CurieBorn 1859 – Died 19061898 – Together they discovered polonium and radium by fractionation of pitchblende, which is an ore (metal-bearing mineral mass) which has a uranium yield between 50-80%.
9Ernest Rutherford Born 1871 – Died 1937 1899 – discovered alpha and beta rays from uraniumExposed a beam of both alpha and beta rays to a magnetic field.The beta rays bent in the field, the alpha rays did not.(Bending in a magnetic field is the sign of charged particles)Beta radiation is a stream of particles not a ray.The charge-to-mass ratio of beta radiation was shown to be the same as that of a beam of electronsBeta radiation is a stream of fast-moving electrons
10Rutherford (continued) 1902 – was able to bend the beam of alpha radiation in both an electric and magnetic field proving it was a stream of particles and not a ray.Alpha particles deflect in the opposite direction of beta particles and are therefore positively chargedLater found that the charge-to-mass ratio of an alpha particle is the same as that of a hydrogen ionAlpha particles have a mass that is twice that of a hydrogen atom.1908 – Rutherford established that alpha particles were helium atoms with two electrons missing
11Paul Villard X-rays -> 102 – 10-3 nm 1900 – discovered gamma raysThey were later given the name gamma rays by Rutherford.The gamma rays were emitted from radium and were not affected by electric or magnetic fieldsRecognized them as being different from X-rays because they had a much greater penetrating depthThis is due to gamma rays having a much shorter wavelength than X-rays.X-rays -> 102 – 10-3 nmgamma rays -> 10-1 – 10-5 nm