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AM1: Atomic Structure Chapters 38 and 39 Atom Atom-The smallest division a particle can be divided into and still maintain the properties. The Development of the Atomic Theory • First theory of the atom: • Greek Philosopher Democritus 400 BC - “atom” (means- “unable to be cut or divided”) Second try • John Dalton in 1808 1. Atoms can not be divided 2. All atoms of a given element were exactly the same 3. Atoms of different elements could join to form compounds • Used the law of definite proportions. • Says a chemical compound always contains the same elements in exactly the same proportions. • Ex. water Third try J.J. Thomson in 1897 - First to say atom could be broken into smaller parts -He discovered the “electron” -Theorized that an atom was made of negative particles scattered throughout positive matter. - He called this the -“plum pudding theory” Thomson found this “negatively” charged particle when he did experiments with the cathode ray http://www.youtube.com/watch?v=O9Goyscbazk • When a magnet was brought near the ray it deflected away from the magnet! There had to be something in the atoms that was negatively charged! Fourth try Rutherford 1908 - Majority of atom is empty space -With a large dense positive center in the atom --the nucleus - the negatively charged electrons orbit around the nucleus experiment http://www.youtube.com/watch?v=5pZj0u_XMbc • “Rutherford” performed the “gold-foil experiment” Shot photon beam at a gold foil. Most of the beams went straight through, but some were deflected off to the side. Extra information found! Chadwick 1935 -found the neutron in the nucleus - Neutron-An electrically neutral particle found in the nucleus of an atom Bohr Model-“Planetary Model” Electrons orbit in energy levels Subatomic Particle Location Charge Mass (AMU) Proton Nucleus + 1 Neutron Nucleus 0 1 Electron Outside the nucleus - 0 Proton Element Element-Substance made of only one kind of atom. Periodic Table of Elements Periodic Table of Elements-Chart that lists elements by atomic number and by electron arrangement Element Key Atomic Number = number of protons Proton-A positively charged particle found in the nucleus of atoms 6 Element symbol C carbon 12.011 Element name Average atomic mass =the average mass of all the isotopes of an element, this is weighted Mass number- the whole number based on the average atomic mass. Ex. Carbon would have the mass number of 12. It is equal to the number of protons + neutrons found in the nucleus. Isotope Isotope-A form of an element that has the same number of protons but a different number of neutrons. Ion Ion-Charged atom due to the loss or gain of electrons If an atom gains electrons, becomes negatively charged (anion) If an atom loses electrons, becomes positively charged (cation) Explanation of the Atom WKRP – Venus explains the atom http://www.youtube .com/watch?v=hhb qIJZ8wC