Ch. 7: Atomic Structure and Periodicity 7.10 History of Periodic Table

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

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

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

Ch. 7 Atomic Structure and Periodicity 7.11 Aufbau Principle and Periodic Table

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

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

Rules for Arrangements

Order for Filling Sublevels

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

Noble Gas Notation  short hand for larger atoms  configuration for the last noble gas is abbreviated by the noble gas’s symbol in brackets

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

Chlorine  number of electrons: 17  last electron is in sublevel: 3p 2p 3s 3p 1s 2s

Sodium  number of electrons: 11  last electron is in sublevel: 3s 1s 2 2s 2 2p 6 3s 1 1s 2s 2p3s

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

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

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

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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