Ch. 7: Atomic Structure Ch. 7: Atomic Structure and Periodicityand Periodicity

7.10 History of Periodic Table7.10 History of Periodic Table

Early PatternsEarly Patterns

DobereinerDobereiner discovered patternsdiscovered patterns triadstriads- groups of 3 elements - groups of 3 elements

with similar propertieswith similar properties NewlandsNewlands

discovered repeating discovered repeating propertiesproperties

octavesoctaves- every eighth element- every eighth element had similar propertieshad similar properties

Periodic TablePeriodic Table Russian, Dmitri MendeleevRussian, Dmitri Mendeleev when he arranged them by atomic when he arranged them by atomic

mass, he found similar properties at mass, he found similar properties at certain intervalscertain intervals

published the first periodic table in published the first periodic table in 18691869

left empty spaces where he left empty spaces where he predicted undiscovered elements predicted undiscovered elements should beshould be

confirmed his predictions and confirmed his predictions and persuaded other chemistspersuaded other chemists

Periodic TablePeriodic Table

Meyer also created a similar Meyer also created a similar table to Mendeleev’s but did table to Mendeleev’s but did not make the same predictionsnot make the same predictionsof elements to comeof elements to come

In 1911, Henry Moseley (English) In 1911, Henry Moseley (English) found that the pattern workedfound that the pattern workedbest if arranged by number of best if arranged by number of protonsprotons

Ch. 7 Atomic Structure Ch. 7 Atomic Structure and Periodicityand Periodicity

7.11 Aufbau Principle and 7.11 Aufbau Principle and Periodic TablePeriodic Table

Rules for ArrangementsRules for Arrangements

Aufbau Principle-Aufbau Principle- an an electron occupies the electron occupies the lowest-energy orbital lowest-energy orbital that can receive itthat can receive it

Beginning in the 3Beginning in the 3rdrd energy level, the energy level, the energies of the energies of the sublevels in different sublevels in different energy levels begin to energy levels begin to overlapoverlap

Rules for ArrangementsRules for Arrangements

Pauli Exclusion Principle-Pauli Exclusion Principle- no two no two electrons in the same atom can have electrons in the same atom can have the same set of 4 quantum numbersthe same set of 4 quantum numbers

Hund’s Rule-Hund’s Rule- orbitals of equal energy orbitals of equal energy are each occupied by one electron are each occupied by one electron before any orbital is occupied by a before any orbital is occupied by a secondsecond

all unpaired electrons must have the all unpaired electrons must have the same spinsame spin

Rules for ArrangementsRules for Arrangements

Order for Filling Sublevels Order for Filling Sublevels

Writing ConfigurationsWriting Configurations

Start by finding the number of electrons in Start by finding the number of electrons in the atomthe atom

Identify the sublevel that the last electron Identify the sublevel that the last electron added is in by looking at the location in added is in by looking at the location in periodic tableperiodic table

Draw out lines for each orbital beginning Draw out lines for each orbital beginning with 1s and ending with the sublevel with 1s and ending with the sublevel identifiedidentified

Add arrows individually to the orbitals until Add arrows individually to the orbitals until all electrons have been drawnall electrons have been drawn

Noble Gas NotationNoble Gas Notation

short hand for larger atomsshort hand for larger atoms configuration for the last noble gas is configuration for the last noble gas is

abbreviated by the noble gas’s symbol in abbreviated by the noble gas’s symbol in bracketsbrackets

Silicon Silicon number of electrons: 14number of electrons: 14 last electron is in sublevel: 3plast electron is in sublevel: 3p

1s 2s 2p 3s 3p

Valence Electrons- the electrons in the outermost energy level

ChlorineChlorine number of electrons: 17number of electrons: 17 last electron is in sublevel: 3plast electron is in sublevel: 3p

2p 3s 3p 1s 2s

SodiumSodium

number of electrons: 11number of electrons: 11 last electron is in sublevel: 3slast electron is in sublevel: 3s

1s1s22 2s 2s22 2p 2p66 3s3s11

1s 2s 2p 3s

CalciumCalcium

number of electrons: 20number of electrons: 20 last electron is in sublevel: 4slast electron is in sublevel: 4s

1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s22

1s 2s 2p 3s

3p 4s

BromineBromine

number of electrons: 35number of electrons: 35 last electron is in sublevel: 4plast electron is in sublevel: 4p

1s1s22 2s 2s22 2p 2p66 3s 3s22 3p 3p66 4s 4s2 2 3d3d1010 4p 4p55

1s 2s 2p 3s 3p

4s 3d 4p

1s 2s 2p 3s 3p

4s 3d 4p

ArgonArgon

number of electrons: 18number of electrons: 18 last electron is in sublevel: 3plast electron is in sublevel: 3p

1s1s22 2s 2s22 2p 2p66 3s3s22 3p 3p66

1s 2s 2p 3s 3p

ExceptionsExceptions ChromiumChromium

expected: [Ar] 4sexpected: [Ar] 4s22 3d 3d44

observed: [Ar] 4sobserved: [Ar] 4s11 3d 3d55

CopperCopper expected: [Ar] 4sexpected: [Ar] 4s22 3d 3d99

observed: [Ar] 4sobserved: [Ar] 4s11 3d 3d1010

not understood not understood but may be because it is more stable to but may be because it is more stable to

have full sublevel or half-filled sublevelhave full sublevel or half-filled sublevel

Practice QuizPractice Quiz Review QuizReview Quiz