Development of Development of the Periodic the Periodic

TableTable

Johann Doberiener Johann Doberiener (1829)(1829)

Arranged elements in groups of three Arranged elements in groups of three (triads)(triads)

For example:For example:

Cl (mass 35)Cl (mass 35)

Br (mass 80)Br (mass 80)

I (mass 127)I (mass 127)

Note: Average mass of the extreme Note: Average mass of the extreme elements =mass of the middle elementelements =mass of the middle element

John Newland (1865)John Newland (1865)

Arranged elements based on the law Arranged elements based on the law of octaves.of octaves.

Elements were arranged by Elements were arranged by increasing atomic massincreasing atomic mass

The chemical properties of the The chemical properties of the elements repeated every 8elements repeated every 8thth element. element.

Lothar Meyer (1867)Lothar Meyer (1867)

Father of the Modern Periodic table.Father of the Modern Periodic table. Based on increasing atomic massBased on increasing atomic mass Chemical properties of elements Chemical properties of elements

reoccur in a periodic fashion.reoccur in a periodic fashion.

Dmitri Mendelyeev (1869)Dmitri Mendelyeev (1869)(Russian chemist)(Russian chemist)

Like Meyer prepared a table based on Like Meyer prepared a table based on increasing atomic mass.increasing atomic mass.

Consisted of 17 columns with 63 elementsConsisted of 17 columns with 63 elements Widely acceptedWidely accepted Constantly revised as new masses were Constantly revised as new masses were

discovereddiscovered Left vacant spots for new elements (Ga, Left vacant spots for new elements (Ga,

Cd,Ge,Tc, Re, Po)Cd,Ge,Tc, Re, Po) Certain discrepancies as new masses were Certain discrepancies as new masses were

found: Ar and K, Co and Ni, Te and Ifound: Ar and K, Co and Ni, Te and I

Henry Mosley (1913)Henry Mosley (1913)

English scientist used x-rays to English scientist used x-rays to determine atomic number (number determine atomic number (number of protons)of protons)

Discovered that the properties of Discovered that the properties of elements were periodic functions of elements were periodic functions of their atomic numbers,their atomic numbers,

Many of the discrepancies Many of the discrepancies disappeared.disappeared.

Present arrangementPresent arrangement Based on increasing Based on increasing atomic numberatomic number Periodic LawPeriodic Law: properties of the elements depend : properties of the elements depend

on the structure of the atom and vary with the on the structure of the atom and vary with the atomic number in a systematic wayatomic number in a systematic way

Horizontal rows are called Horizontal rows are called periods periods (#1-7) (#1-7) Indicates the number of principal energy levels.Indicates the number of principal energy levels.

Note: Lanthanide series part of period 6—long period Note: Lanthanide series part of period 6—long period and Actinide series part of period 7—unfinished and Actinide series part of period 7—unfinished periodperiod

Properties of elements Properties of elements change change within a periodwithin a period Vertical columns are called Vertical columns are called groups groups or or families families (#1-(#1-

18)18)Indicates the number of valence electrons.Indicates the number of valence electrons.Elements within a group have similar properties. Elements within a group have similar properties.

Ex.Na and Li Ex.Na and Li

Element KeyElement Key