Chapter 5 The Periodic Law

Chapter 5: The Periodic Law 5.1 History of the Periodic Table 5.2 Electron Configuration and the Periodic Table 5.3 Electron Configuration and Periodic Properties

Modern Russian Table

Chinese Periodic Table

Orbital Filling Table

Periodic Table with Group Names

Chapter 5 The Periodic Law 5.1 History of the Periodic Table

Predecessors to the Modern Periodic Table Dobereiner’s Triads J.W. Dobereiner classified some elements into groups of three, which he called triads. similar chemical propertiessimilar chemical properties physical properties varied in an orderly way according to their atomic masses.physical properties varied in an orderly 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 Lavoisier

Stanislao Cannizzaro Stanislao Cannizzaro ( ) 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 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 reactions Dmitri Mendeleev

Mendeleev’s Periodic Table Dmitri Mendeleev

Predecessors to the Modern Periodic Table Mendeleev’s Periodic Table repeated in an orderly way increasing atomic mass Dmitri Mendeleev realized that the chemical and physical properties of the elements repeated in an orderly way when he organized the elements according to increasing atomic mass. In 1869, Mendeleev published a table of the elements organized by increasing atomic mass. FatherMendeleev was a Russian scientist and is often referred to as the “Father” of the Periodic Table. PeriodicityPeriodicity is the tendency to recur at regular intervals.

Mendeleev’s Table Mendeleev’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 Table Mendeleev made some exceptions to place elements in rows with similar telluriumiodine's properties (tellurium & iodine'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) Vertical Vertical column s in atomic weight order Horizontal Horizontal rows have similar chemical properties

Problems with Mendeleev’s Table Moseley helped to clarify some of the problems… Why didn't some elements fit in order of increasing atomic mass? Why did elements exhibit periodic behavior?

Henry Moseley 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 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 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 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 Law The physical and chemical properties of the elements are periodic functions of their atomic numbers

Discovery of the Noble Gases Helium discovered as a component of the sun, based on the emission spectrum of sunlight Freidrich Dorn discovers radon William Ramsay discovers argon Ramsay finds helium on Earth Ramsay discovers krypton and xenon Sir William Ramsay

The LanthanidesThe Lanthanides Early 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 Actinides Discovery (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.