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RAD 354 Chapt 2 Structure of Matter • The atom is the smallest part of an element that has all the properties of the element – 112 elements have been identified 92 are natural 20 were artificially produced Interesting dates - info • 1808 John Dalton classified elements according to atomic mass values • Mendeleev first suggested the periodic table with 8 groupings – Atomic number (Z#)= NUMBER OF PROTONS – Atomic MASS # = elemental mass (A) AND neutrons Nuclear model of the atom • 1911 Ernest Rutherford introduced the nuclear model of the atom • 1913 Niels Bohr improved on Rutherford’s • The “mini solar system” model is now know as the Rutherford – Bohr model of the atom Molecules • Atoms of various elements may combine to forms moledules – Sodium (Na) + chlorine (CL) = sodium chloride (NaCL) = table salt Chemical Compound • Is a NEW substance that is formed when two or more atoms of different elements combine – Covalent bond – sharing electrons in outer orbital shells – Ionic bonding – atoms attracted to each other because of opposite charges • Smallest particle of an element is an atom • Smallest particle of a compound is a molecule Atoms • Three main parts: – Electrons – Protons – Neutrons • Mass of an atom is expressed in atomic mass units (AMU’s) {1/2 mass of a carbon 12 atom} -AMU’s are always rounded numbers! Electron “shells” /Orbitrons • Shells are lettered K,L,M,N – etc from the nucleus outward (also numbered 1,2,3,4,5 from the nucleus outward). • Max POTENTIAL number of electrons in any shell 2n2 • The number of electrons in the outer most shell tells which GROUP and PERIOD it exists in the periodic table Varied #’s of mass# & atomic# • Isotope = same # of protons but different # of neutrons • Isobar = different # of protons and neutrons BUT same TOTAL number of nucleons • Isotones = same # of neutrons BUT different # of protons • Isomer = same atomic number and same atomic mass number- BUT exist at different energy states (varied nuclear arrangements) Radioactivity • Can be emission of alpha, beta or gamma • Radioactive HALF LIFE = time required for a quantity of radioactivity to be reduced (decay) to ½ of it’s original value. NOTE: it will have the same specific energy constant – BUT only half the number of decays Particulate vs electromagnetic • Which of alpha, beta and gamma are particulate? • Which is/are electromagnetic?