Development of theDevelopment of thePeriodic TablePeriodic Table

OrOr

““The History of the Modern Periodic TableThe History of the Modern Periodic Table””

• Introduction– The periodic table is made up of rows of elements

and columns.

– An element is identified by its chemical symbol.

– The number above the symbol is the atomic number

– The number below the symbol is the roundedatomic weight of the element.

– A row is called a period

– A column is called a group

Elements

• Science has come alongway since Aristotle’stheory of Air, Water, Fire,and Earth.

• Scientists have identified90 naturally occurringelements, and createdabout 28 others.

• Periodic Patterns– The chemical behavior of elements is determined

by its electron configuration

– Energy levels are quantized so roughly correspondto layers of electrons around the nucleus.

– A shell is all the electrons with the same value of n.• n is a row in the periodic table.

– Each period begins with a new outer electron shell

During the nineteenth century,chemists began to categorize theelements according to similarities

in their physical and chemicalproperties. The end result ofthese studies was our modern

periodic table.

Johann Dobereiner

1780 - 1849Model of triads

In 1829, he classified some elements intogroups of three, which he called triads.The elements in a triad had similarchemical properties and orderly physicalproperties.

(ex. Cl, Br, I andCa, Sr, Ba)

John Newlands

1838 - 1898Law of Octaves

In 1863, he suggested that elements bearranged in “octaves” because he noticed(after arranging the elements in order ofincreasing atomic mass) that certainproperties repeated every 8th element.

John Newlands

1838 - 1898 Law of Octaves

Newlands' claim to see a repeating pattern was metwith savage ridicule on its announcement. Hisclassification of the elements, he was told, was asarbitrary as putting them in alphabetical order andhis paper was rejected for publication by theChemical Society.

John Newlands

1838 - 1898 Law of Octaves

His law of octaves failed beyond theelement calcium. WHY?

Would his law of octaves work today withthe first 20 elements?

In 1869 he published a table of theelements organized by increasing atomicmass.

Dmitri MendeleevDmitri Mendeleev

1834 - 1907

Lothar Meyer

1830 - 1895

At the same time, he published his owntable of the elements organized byincreasing atomic mass.

• Both Mendeleev and Meyer arrangedthe elements in order of increasingatomic mass.

• Both left vacant spaces where unknownelements should fit.

So why is Mendeleev called the “fatherof the modern periodic table” and notMeyer, or both?

• stated that if the atomic weight of an elementcaused it to be placed in the wrong group, then theweight must be wrong. (He corrected the atomicmasses of Be, In, and U)

• was so confident in his table that he used it topredict the physical properties of three elementsthat were yet unknown.

• After the discovery of these unknown elementsbetween 1874 and 1885, and the fact thatMendeleev’s predictions for Sc, Ga, and Ge wereamazingly close to the actual values, his table wasgenerally accepted.

Mendeleev...

Henry Moseley

1887 - 1915

In 1913, through his work with X-rays, hedetermined the actual nuclear charge(atomic number) of the elements*. Herearranged the elements in order ofincreasing atomic number.*“There is in the atom a fundamentalquantity which increases by regularsteps as we pass from each element tothe next. This quantity can only be thecharge on the central positive nucleus.”

Henry Moseley

His research was halted when the Britishgovernment sent him to serve as a footsoldier in WWI. He was killed in thefighting in Gallipoli by a sniper’s bullet, atthe age of 28. Because of this loss, theBritish government later restricted itsscientists to noncombatant duties duringWWII.

Glenn T. SeaborgAfter co-discovering 10 new elements, in1944 he moved 14 elements out of themain body of the periodic table to theircurrent location below the Lanthanideseries. These became knownas the Actinide series.

1912 - 1999

Glenn T. SeaborgHe is the only person to have an elementnamed after him while still alive.

1912 - 1999

"This is the greatest honor ever bestowedupon me - even better, I think, thanwinning the Nobel Prize."

Periodicclassification

ofelements

A periodic table ofpartial ground-state

electron configurations

The Periodic Law– Similar physical and chemical properties recur

periodically when the elements are listed in order ofincreasing atomic number.

– Each period ends with a completely filled outer shellthat has the maximum number of electrons for thatshell.

– The number identifying the A families identifies thenumber of electrons in the outer shell, excepthelium.

– The outer shell electrons are responsible forchemical reactions.

– Group A elements are called representativeelements.

– Group B elements are called transition elements.