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Published byAugustine Carter Modified over 9 years ago
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Unit 3: Atomic Structure Atomic Number, Mass Number, and Isotopes
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After today, you will be able to… Find the atomic mass, atomic number, and symbols of elements off of the Periodic Table Calculate the number of neutrons in a particular atom Explain what an isotope is
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Atomic Number The number of protons in the element. Always a whole number Example: Oxygen’s atomic number is 8, so there are 8 protons in Oxygen’s nucleus
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Atomic Number For neutral elements (no charge) the # of p + = # of e - The number of protons will never change for an element It is like our social security number, it identifies them.
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Atomic Mass Read right off the Periodic Table. The number will have a decimal. It is the average (weighted) of all the elements isotopes.
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Atomic Number vs. Atomic Mass 8 O Oxygen 15.999 Atomic number Atomic mass
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Mass Number Number of protons & neutrons combined Always a whole number
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Finding the Number of Neutrons Neutrons = mass # - atomic # Example: Oxygen’s mass number is 16 and its atomic number is 8. The number of neutrons will be 16-8 = 8.
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Isotopes Atoms with the same number of protons, but different number of neutrons. They are chemically alike Have different mass numbers Written like this: Element–Mass Number
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Examples: Neutral hydrogen isotopes Hydrogen-1 Hydrogen-2Hydrogen-3 1 proton 1 proton 1 proton 1 electron 1 electron 1 electron 0 neutrons1 neutron2 neutrons
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Summary Atomic # = protons = electrons (neutral atoms) Mass # = protons + neutrons = rounded atomic mass Neutrons = mass # - atomic #
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Practice makes perfect… Element Symbol Atomic Number Mass Number # of Protons # of Neutrons # of electrons S 16 714 17 18 4020 163216 N Cl Ca 777 35 17 20
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