Chapter 5Chapter 5The Periodic LawThe Periodic Law

Chapter 5: The Periodic Law

5.1 History of the Periodic Table5.2 Electron Configuration and the Periodic

Table5.3 Electron Configuration and Periodic

Properties

Modern Russian TableModern Russian Table

Chinese Periodic TableChinese Periodic Table

Orbital Filling TableOrbital Filling Table

Periodic Table with Group NamesPeriodic Table with Group Names

Chapter 5Chapter 5The Periodic LawThe Periodic Law

5.1 History of the Periodic Table

Predecessors to the Modern Periodic Predecessors to the Modern Periodic TableTable

• Dobereiner’s TriadsJ.W. Dobereiner classified some elements into groups of three, which he called triads.

• similar chemical propertiessimilar chemical properties• physical properties varied in an orderly physical properties varied in an orderly

way according to their atomic masses.way according to their atomic masses.

Searching For an Organizing Principle

– Chlorine, bromine, and iodine have very similar chemical properties.

• 1750 only 17 elements known• 1789 Antoine Lavoisier grouped

known elements (4 groups)– Metals– Non-metals– Gases– Earths

• Next 80 yrs scientists looked for better way to classify known elements

Antoine LavoisierAntoine Lavoisier

Stanislao CannizzaroStanislao Cannizzaro(1826-1910)

• Italian chemist• Determined a method

for accurately measuring the relative masses of atoms

• His method allowed chemists to search for a relationship between atomic mass and other properties of elements

Mendeleev’s Periodic TableMendeleev’s Periodic Table• 1869….Dmitri Mendeleev (Russian

teacher and chemist) organized known elements while playing solitaire (about 70 known)– Made deck of cards with

elements– Listed name, mass and

properties• Paid attention to how elements

reacted in chemical reactionsDmitri MendeleevDmitri Mendeleev

Mendeleev’s Periodic TableMendeleev’s Periodic Table

Dmitri MendeleevDmitri Mendeleev

Predecessors to the Modern Periodic Predecessors to the Modern Periodic TableTable

• Mendeleev’s Periodic TableDmitri Mendeleev realized that the chemical and physical properties of the elements repeated in an repeated in an orderly wayorderly way when he organized the elements according to increasing atomic massincreasing atomic mass.

• In 1869, Mendeleev published a table of the elements organized by increasing atomic mass.

• Mendeleev was a Russian scientist and is often referred to as the “FatherFather” of the Periodic Table.

• PeriodicityPeriodicity is the tendency to recur at regular intervals.

Mendeleev’s TableMendeleev’s Table"The chemical properties of the elements are a periodic

function of their atomic weights"

He called this element eka-Aluminum.

Later it was renamed Gallium after its

discovery in 1875

Mendeleev's Periodic TableMendeleev's Periodic Table

• Mendeleev made some exceptions to place elements in rows with similar properties (telluriumtellurium & iodine'siodine's places were switched)

• Missing ElementsMissing Elements: gaps existed in Mendeleev’s table• Mendeleev predicted the properties of the “yet to be

discovered” elements(scandium, germanium and gallium)

VerticalVertical column

s in atomic weight order

HorizontalHorizontal rows have similar chemical properties

Problems with Mendeleev’s TableProblems with Mendeleev’s Table

Moseley helped to clarify some of the problems…

Why didn't some Why didn't some elements fit in order of elements fit in order of

increasing atomic increasing atomic mass?mass?

Why did elements exhibit Why did elements exhibit periodic behavior?periodic behavior?

Henry Moseley 1887-1915Henry Moseley 1887-1915• English physicist who determined

the number of positive charges in the nucleus (protons) by measuring the wavelength of the x-rays given off by certain metals in 1913.

• He was killed by a sniper in Turkey in August 1915 during WWI. Many people think that Britain lost a future Nobel Prize winner. This is because Nobel Prizes, the most prestigious awards for scientific achievement are awarded only to living people.

Moseley and the Periodic Table Moseley and the Periodic Table • Protons and Atomic Number:

X-ray experiments revealed a way to determine the number of protons in the nucleus of an atom

The periodic table was found to be in atomic The periodic table was found to be in atomic number order, not atomic mass order!!!number order, not atomic mass order!!!

• This explained tellurium-iodine anomaly

• ***Moseley was killed in battle in 1915, during WWI. He was 28 years old

The Periodic LawThe Periodic Law The physical and chemical properties of the

elements are periodic functions of their atomic numbers

Discovery of the Noble Gases

1868 1894 1895 1898 1900

Helium discovered as a component of the sun, based on the emission spectrum of sunlight

Freidrich Dorn

discovers radon

William Ramsay discovers

argonRamsay

finds helium on Earth

Ramsay discovers

krypton and xenon

Sir William Ramsay

• The LanthanidesThe LanthanidesEarly 1900's the elements from cerium (#58) to lutetium (#71) are separated and identified. Also known as the rare earth elements, less than 0.01% naturally occurring.

• The ActinidesThe ActinidesDiscovery (or synthesis) of thorium, # 90 to lawrencium #103

• Both groups pulled out of the table for space reasons. • Periodicity:

Elements with similar properties are found at regular intervals within the "periodic" table

The Periodic Law• The periodic law: When elements are

arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.

– The properties of the elements within a period change as you move across a period from left to right.

– The pattern of properties within a period repeats as you move from one period to the next.

In the modern periodic table, elements are arranged in order of increasing atomic number.

Squares in the Periodic Table•The periodic table displays the symbols and names of the elements, along with information about the structure of their atoms.