Atomic Theory Notes
Transcription
Atomic Theory Notes
Atomic Theory Democritus 400 B.C. Earth Air Fire Water Greek “Thinkers” 1. 2. 3. Atoms – “indivisible” – smallest part of an element that retains the property of that element All atoms have a definite size (“incompressible”) All atoms are neutral All matter is composed of atoms too small to be seen which cannot be divided. Greek “Thinkers” 4. 5. 6. There is empty space between atoms Atoms are completely solid Later proved incorrect Atoms are different sizes, shapes, and weights Alchemists Middle Ages Spent most of their time trying to change metals into silver and gold Transmutation – changing one element into another Added knowledge about the properties of elements Antoine Lavoisier 1789 Able to list 33 known elements Law of Conservation of Mass “Recycling” Law Matter can be changed; BUT it cannot be created or destroyed. John Dalton 1803 “The Father of Modern Atomic Theory” Used all former ideas to come up with his atomic theory John Dalton 1. 2. 3. Each element consists of individual atoms All atoms of the same element are identical in mass and properties All atoms of different elements are different in mass and properties John Dalton 4. 5. Atoms combine with each other in specific ratios to make compounds Chemical reactions occur when atoms are separated, joined, or rearranged, but the atoms of one element are not changed into the atoms of another by chemical reaction 1869 Russian Dmitri Mendeleev Scientist Devised the Periodic Table Arranged the known elements by atomic weight and noticed that properties re-occurred periodically Left blanks for undiscovered elements 400-1890’s Atom was viewed as solid and indivisible Marie & Pierre Curie Henri Becquerel Discovered Radioactivity Polonium (Po), Radium (Ra), Uranium (U) Smaller particles are emitted from the atom Gamma Rays – neutral Beta rays – negative (electron) Alpha rays – positive (2 protons & 2 neutrons) J.J. Thomson Discovered the electron using the cathode ray tube Electrons are NEGATIVE particles e- are very small in weight Plum pudding model Later found positive particles (protons) Robert Millikan Determined (9.11 This the mass of the e- x 10-31 kg) mass is MUCH smaller than the mass of the proton Ernest Rutherford Gold foil experiment Found an atom has a very small positive nucleus surrounded by tiny moving e and lots of empty space Modern Gold Foil Protons must be in center Experiment James Chadwick Discovered No the neutron charge Same weight as proton Atomic Structure Subatomic Particles protons (p+) = positive electrons (e-) = negative neutrons (n0) = neutral Atomic Structure Atomic number = # p+ Bromine A.N. = 35 35 protons Protons determine the element Atomic Structure Atoms are neutral protons (p+) = # electrons (e-) Bromine # a.n. = 35 35 protons (+) Therefore, 35 electrons (-) Atomic Structure Atomic The Mass weight of the atom is in the nucleus Protons and Neutrons in the nucleus Atomic mass = #p+ + #n0 Bromine a.m. = 80 80 = 35 + #n0 #n0 = 45 Atomic Structure Atoms are neutral # protons (p+) = # electrons (e-) Atomic number = # p+ Atomic mass = #p+ + #n0 = neutrons = protons C-14 C-12 Nucleus Nucleus = neutrons = protons C-14 C-12 Nucleus Nucleus -Both are Carbon (both have 6 protons) -Have different number of neutrons! Isotopes Atoms of the same element (same atomic number) with different atomic masses (different # of neutrons). C-14 and C-12
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