Presentation on theme: "1 Reactions History Great Pyramids 2900 BCE Atomic Theory Founders of Law of Conservation of Mass 1785 Atomic Theory of Matter 1803 Law of Definite Proportions."— Presentation transcript:
1 Reactions History Great Pyramids 2900 BCE Atomic Theory Founders of Law of Conservation of Mass 1785 Atomic Theory of Matter 1803 Law of Definite Proportions 1797 Radioactivity Value of Pi 240 BCE Algebra 820 Admission charged for a concert 1672 Civil War st McDonald’s BCE Main Menu
2 Reactions History Leucippus and Democritus Atomic Theory Matter is made up of indivisible particles called atoms - atom comes from the Greek “atomos” meaning uncuttable Atoms are completely solid with no internal structure Atoms differ in size, shape and weight Leucippus of Miletus (circa B.C.E.) originated the concept of the atom Democritus of Abdera (circa 460 –371 B.C.E.) was a pupil of Leucippus.
3 Reactions History Born 1743 – Died 1794 French Chemist Law of Conservation of Mass First modern chemical textbook Law of Conservation of Mass Total mass of Reactants Total mass of Products = Antoine Lavoisier In a chemical reaction, mass is neither created nor destroyed
4 Reactions History Born 1754 – Died 1826 French Chemist 1797 Law of Definite Proportions (also known as Law of Constant Composition) Law of Definite Proportions Generalized that the elements in all compounds are present in fixed proportions by weight. Showed that copper carbonate must always be composed of the same fixed proportions of copper, carbon and oxygen. Joseph Proust
5 Reactions History John Dalton Born Died 1944 British Chemist and Physicist Developed the atomic theory of matter Dalton’s Atomic Theory Each element is composed of extremely small particles called atoms Compounds contain atoms of two or more elements Atoms are neither created nor destroyed in a chemical reaction All atoms of a particular element are identical, atoms of different elements have different properties
6 Reactions History Wilhelm Roentgen Born 1845 – Died – discovered X-rays (called them Roentgen’s rays) German Physicist Awarded Nobel Prize in 1901 for the discovery of the X-rays While experimenting with a Crookes tube, he discovered a new type of ray emitted from the tube which would cast shadows of solid objects These rays pass through most substances, including the soft tissue of the body, and leave bones and solid metals visible
7 Reactions History Antoine-Henri Becquerel 1896 – 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. Born 1852 – Died 1908 French Scientist
8 Reactions History Marie Curie Born 1867 – Died 1934 Pierre Curie Born 1859 – Died – observed that thorium compounds also emit becquerel rays. Invented the word “radioactivity” to describe this behavior – Together they discovered polonium and radium by fractionation of pitchblende, which is an ore (metal-bearing mineral mass) which has a uranium yield between %.
9 Reactions History Ernest Rutherford 1899 – discovered alpha and beta rays from uranium Exposed 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 electrons Beta radiation is a stream of fast-moving electrons Born 1871 – Died 1937
10 Reactions History Rutherford (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 charged Later found that the charge-to-mass ratio of an alpha particle is the same as that of a hydrogen ion Alpha particles have a mass that is twice that of a hydrogen atom – Rutherford established that alpha particles were helium atoms with two electrons missing
11 Reactions History 1900 – discovered gamma rays The gamma rays were emitted from radium and were not affected by electric or magnetic fields Recognized them as being different from X-rays because they had a much greater penetrating depth This is due to gamma rays having a much shorter wavelength than X-rays. X-rays -> 10 2 – nm gamma rays -> – nm They were later given the name gamma rays by Rutherford. Paul Villard