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Democritus Ernest Rutherford 1871-1937 460 BC New Zealand physicist Greek philosopher proposes the existence of the discovered the nucleus. atom. His Theory: Hi...

Democritus Ernest Rutherford 1871-1937 460 BC New Zealand physicist Greek philosopher proposes the existence of the discovered the nucleus. atom. His Theory: His Theory: -​ Small, dense, positively charged particle All atoms: present in nucleus called a proton -​ Are small hard particles -​ Electrons travel around the nucleus, but -​ Are made of a single material formed into their exact places cannot be different shapes and sizes described. -​ Are always moving, and they form different materials by joining together Rutherford’s Model Nuclear Model Aristotle Niels Bohr 1913 He did not think there was a limit to the number Danish physicist; discovered energy levels. of times matter could be divided. His Theory: He thought that all substances were built up from -​ Electrons travel around the nucleus in only four elements. definite paths and fixed distances. Earth Fire -​ Electrons can jump from one level to a Water Air path in another level. Bohr’s Model John Dalton 1766-1844 In Bohr’s model, electrons move with British chemist constant speed in fixed orbits around His Theory: the nucleus, like planets around a sun. -​ All substances are made of atoms that cannot be created, divided, or destroyed. Bohr proposed that electrons move in -​ Atoms join with other atoms to make new paths at certain distances around the nucleus. substances. Electrons can jump from a path on one level to a -​ Atoms of the same element are exactly path on another level. alike, and atoms of different elements are different in mass and size. Erwin Schrodinger 1924 Austrian physicist; developed the electron cloud Dalton’s Model model. Solid Sphere Model or Bowling His Theory: Ball Model -​ The exact path of electrons cannot be predicted. J.J. Thomson 1856-1940 -​ The region referred to as the electron English chemist and physicist; discovered 1st cloud, is an area where electrons can subatomic particles. likely be found. His Theory: -​ Atoms contain negatively charged Erwin Schrodinger’s Model Electron particles called electrons and positively Cloud Model charged matter. James Chadwick 1932 Created a model to describe the atom as a English physicist; discovered neutrons sphere filled with positive matter with negative His Theory: particles mixed in Referred to it as the plum -​ Neutrons have no electrical charge. pudding model -​ Neutrons have a mass nearly equal to the mass of a proton. J.J. Thomson’s Model -​ Unit of measurement for subatomic Plum Pudding Model or Raisin particles is the atomic mass unit (amu). Bun Model Dalton’s Atomic Theory That “atoms of the same element are ​ All mater is made up of atoms alike”. ​ An element is made up of one kind of Common characteristics of atom is the number of atom protons in their nuclei- called atomic number (Z) ​ A compound is made up of a combination of diff. kinds of atom that follows a specific ration An atom cannot be created nor destroyed (proven wrong: ISOTOPES) Modern Theory of the Atom 1.​ Atoms are composed of three main subatomic particles: the electron, proton, ISOTOPES and neutron. Atoms of the same element which have 2.​ Most of the mass of the atom is different masses. concentrated in the nucleus of the atom. An atom of a specific 3.​ The protons and neutrons are located isotope is called NUCLIDE. within the nucleus, while the electrons The isotope of an element have different exist outside of the nucleus. numbers of neutrons. 4.​ In stable atoms, the number of protons is equal to the number of electrons. The term isotope is formed from the Greek roots #p = #e isos (ἴσος "equal") and topos (τόπος"place"), ​ The type of atom is determined by the meaning "the same place" number of protons it has. ​ The number of protons in an atom is Two ways to name isotopes equal to the atomic number. 1. Name –mass Number #p = A# therefore #e = A# Ex. C-12 ( read as carbon twelve) ​ The sum of the number of protons and C-13 ( read as carbon thirteen) neutrons in a particular atom is called the 2. Isotopic symbol atomic mass. Ex: 12C6 #p+#e= AM 13 C6 ​ Valence electrons are the outermost electrons. OCTET RULE -​ there should be exactly 8 electrons at the outer part of an atom (valence electrons) in order to be stable. Laws of Matter Laws of Matter Law of Conservation of Mass - states that mass cannot be separated or destroyed in a chemical reaction. HYDROGEN ISOTOPES: Atoms never lose or gain in a chemical reaction; PROTIUM - 99% abundance THEY ARE JUST REARRANGED. DEUTERIUM - 0.05% abundance TRITIUM - radioactive and 10-18% abundance Law of Definite Proportion - elements of a compound are always present in the same proportions by mass. Law of Multiple Proportion (proton, neutron)= nucleus Electron=light The discovery of isotopes contradicted DALTON’S postulate  Many smoke detectors contain a radioactive Americium source, while some photocopiers use Unstable isotopes undergo a process of radioactive Polonium to prevent static buildup. decay or release of subatomic particles Cosmetics, baby powder and contact lens and/or energy spontaneously. solution are sterilized by radiation. These isotopes are considered radioactive. Radioactive Isotopes Americium-241 (Am) ENERGY Cesium-137 (Cs) 1. Nuclear power generation. Nuclear power Cobalt-60 (Co) plants produce 20% of the electricity used in the Iodine-131 (I) Iridium-192 (Ir) US, and 16% worldwide. Plutonium (Pu) 2.Nuclear reactors are also used to power Polonium 210 (Po) submarines, aircraft carriers and spacecraft. Strontium-90 (Sr) 3. Radioisotope thermoelectric generators BIOMEDICAL IMAGING (RTGs) use the energy emitted from radioisotopes to boil water and generate power for remotely located weather stations and navigational buoys. 4. Many pacemakers are also powered by radioactive materials PACEMAKER an artificial device for stimulating the heart muscle and regulating its contractions. MEDICINE 1.Radioisotopes are used to diagnose and treat many medical conditions and diseases, including cancer and thyroid disorders. 2.Imaging procedures such as kidney and bone scans often use radioactive materials because these materials are absorbed by particular part of the body. INDUSTRY 1. Radioactive materials allow many industrial processes to be performed cheaper, faster, easier, and more effectively. Radioactive tracers make it possible to find blockages and leaks in pipes and to determine how quickly materials flow through them. They also allow corrosion and wear and tear on mechanical equipment to be monitored. AGRICULTURE Radiation is used to kill bacteria, molds and other microorganisms in strawberries, onions, potatoes, meats, and spices, preventing the food from spoiling, and making it safer to eat. CONSUMER PRODUCTS n = AM - A# AAM: ​