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Chapter 2

Chapter 2 - Periodic Properties.pdf

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University of British Columbia
CHEM 121
Mark Mac Lachlan

Chapter 2Periodic Properties Atoms and Simple Compounds Atomic Structure Atoms mainly consist of 3 subatomic particles 1 atomic mass unit u112 the mass of Particle Charge Mass u proton 1 10073 1 one atom of carbon12 electron 0 10087 1 241 u1660510 gneutron 1 00005486 0atoms are mostly empty space electrons a n100 000 nucleus n a most of the mass is in the nucleusthe nucleus is composed of protons and neutronselectrons at the periphery of the atom are involved in chemical reactions Symbolic representation of an elementwith mass numberand atomic numberMass Number protons neutronsAtomic Number protons determines the identity of the element Isotopes various forms of the same element which differ only in the number of neutrons contained in the nucleus they generally form the same chemical compounds and react in a similar way Atomic Weight Atomic Weight weighted averages of the masses of naturally occurring isotopes it is calculated by summing up the products of the atomic mass of each isotope and its percent abundanceAtomic Weight isotope 1mass isotope 1 isotope 2mass isotope 2 1213Example A naturally occurring sample of carbon consists of 2 isotopes C exactly 12 u and C 1300335 u Using the atomic weight of carbon from the periodic table 12011 u the natural abundance of each isotope can be determined 1213Let x C and 1x C since the percent abundance must total 100 12011 u12 u11300335 u12 u1300335 u1300335 u 099235 u100335 u0989 or 989 1213Thus the natural abundance of C is 989and the natural abundance of C is 11
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