THE PERIODIC LAWHISTORY OF THE PERIODIC TABLE

Chapter 5.1

Objectives1. Explain the roles of Mendeleev and

Moseley in the development of the periodic table.

2. Describe the modern periodic table.3. Explain how the periodic law can be

used to predict the physical and chemical properties of elements

4. Describe how the elements belonging to a group of the periodic table are interrelated in terms of atomic number.

Early History By 1860 – more than 60 elements

had been discovered. September of 1860 – First

international Congress of Chemists met Cannizzaro – convincing method for

measuring relative atomic mass Became a standard for showing

relationship between atomic mass and properties of elements

Stanislao Cannizzaro

Mendeleev and Periodicity

Interesting facts:

1. Some Atomic masses were out of place

2. Empty spaces for elements not yet discovered. Later they were and fit right in.

Russian Chemist – Dmitri Mendeleev First usable periodic table

Arranged according to : 1. Properties 2. Atomic mass

Moseley and Periodic Law 1911 – Henry Moseley

Working with spectra of 38 metals – elements fit into better patterns when organized according to nuclear charge. Led to :

Modern definition of atomic number Periodic table organized according to

atomic number instead of atomic mass

Periodic Law : The physical and chemical properties of the elements are periodic functions of their atomic numbers.

The Modern Periodic table Define: arrangement of the elements

in order of their atomic number so that elements with similar properties fall in the same column, or group.

The Noble Gases Most significant addition to periodic

table 1894 – John William Strutt and Sir

William Ramsey Discovered Argon 1898 – Ramsay discovered Kr and Xe

1900 – Friedrich Dorn discovered Rn Placed this new group of elements in a new

group Group 18

Noble

G

ase

s

Lanthanides and Actinides Lanthanides – 14 elements with

atomic number from 58 to 71 Cerium to Lutetium (Top row – f-block)

Actinides – 14 elements with atomic number from 90 to 103 Thorium to Lawrencium ( Bottom row – f-block)

To save space – both were set off below main portion of periodic table

What it would look like!

Periodicity Similar periodic pattern repeated with

atomic number Difference in atomic number of similar properties

8, 8, 18, 18, 32 Atomic Number

Difference in atomic number

2 810 8

18 1836 1854 32 86

3 811 819 1837 1855 3287

Periodic Table song by Tom Lehrer There’s antimony, arsenic, aluminum, selenium, And hydrogen and oxygen and nitrogen and rheniumAnd nickel, neodymium, neptunium, germanium, And iron, americium, ruthenium, uranium, Europium, zirconium, lutetium, vanadium And lanthanum and osmium and astatine and radium And gold, protactinium and indium and gallium And iodine and thorium and thulium and thallium. There’s yttrium, ytterbium, actinium, rubidium And boron, gadolinium, niobium, iridium And strontium and silicon and silver and samarium, And bismuth, bromine, lithium, beryllium and barium. There’s holmium and helium and hafnium and erbium And phosphorous and francium and fluorine and terbium And manganese and mercury, molybdinum, magnesium, Dysprosium and scandium and cerium and cesium And lead, praseodymium, platinum, plutonium, Palladium, promethium, potassium, polonium, Tantalum, technetium, titanium, tellurium, And cadmium and calcium and chromium and curium. There’s sulfur, californium and fermium, berkelium And also mendelevium, einsteinium and nobelium And argon, krypton, neon, radon, xenon, zinc and rhodium And chlorine, cobalt, carbon, copper, Tungsten, tin and sodium. These are the only ones of which the news has come to Harvard, And there may be many others but they haven’t been discovered.