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Ch. 7: Atomic Structure and Periodicity 7.10 History of Periodic Table
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Early Patterns Dobereiner discovered patterns discovered patterns triads- groups of 3 elements triads- groups of 3 elements with similar properties Newlands discovered repeating discovered repeatingproperties octaves- every eighth element octaves- every eighth element had similar properties had similar properties
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Periodic Table Russian, Dmitri Mendeleev when he arranged them by atomic mass, he found similar properties at certain intervals published the first periodic table in 1869 left empty spaces where he predicted undiscovered elements should be confirmed his predictions and persuaded other chemists
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Periodic Table Meyer also created a similar table to Mendeleev’s but did not make the same predictions of elements to come In 1911, Henry Moseley (English) found that the pattern worked best if arranged by number of protons
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Ch. 7 Atomic Structure and Periodicity 7.11 Aufbau Principle and Periodic Table
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Rules for Arrangements Aufbau Principle- an electron occupies the lowest-energy orbital that can receive it Beginning in the 3 rd energy level, the energies of the sublevels in different energy levels begin to overlap
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Rules for Arrangements Pauli Exclusion Principle- no two electrons in the same atom can have the same set of 4 quantum numbers Hund’s Rule- orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second all unpaired electrons must have the same spin
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Rules for Arrangements
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Order for Filling Sublevels
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Writing Configurations Start by finding the number of electrons in the atom Identify the sublevel that the last electron added is in by looking at the location in periodic table Draw out lines for each orbital beginning with 1s and ending with the sublevel identified Add arrows individually to the orbitals until all electrons have been drawn
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Noble Gas Notation short hand for larger atoms configuration for the last noble gas is abbreviated by the noble gas’s symbol in brackets
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Silicon number of electrons: 14 last electron is in sublevel: 3p 1s 2s 2p 3s 3p Valence Electrons- the electrons in the outermost energy level
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Chlorine number of electrons: 17 last electron is in sublevel: 3p 2p 3s 3p 1s 2s
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Sodium number of electrons: 11 last electron is in sublevel: 3s 1s 2 2s 2 2p 6 3s 1 1s 2s 2p3s
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Calcium number of electrons: 20 last electron is in sublevel: 4s 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 1s 2s 2p3s 3p 4s
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Bromine number of electrons: 35 last electron is in sublevel: 4p 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 5 1s 2s 2p 3s3p 4s3d 4p 1s 2s 2p 3s3p 4s3d 4p
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Argon number of electrons: 18 last electron is in sublevel: 3p 1s 2 2s 2 2p 6 3s 2 3p 6 1s 2s 2p 3s3p
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Exceptions Chromium expected: [Ar] 4s 2 3d 4 expected: [Ar] 4s 2 3d 4 observed: [Ar] 4s 1 3d 5 observed: [Ar] 4s 1 3d 5 Copper expected: [Ar] 4s 2 3d 9 expected: [Ar] 4s 2 3d 9 observed: [Ar] 4s 1 3d 10 observed: [Ar] 4s 1 3d 10 not understood but may be because it is more stable to have full sublevel or half-filled sublevel
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