Periodic Table History

Early History 1800 – 1860 The elements were still confused with compounds and mixtures Element Compound Mixture

Compounds and Mixtures Element: A pure substance made of only one kind of atom Examples: O2, H2, Diamonds (Carbon) Compound: A substance that is made from the atoms of two or more elements that are chemically bonded. Examples: Water and hydrogen peroxide (hydrogen and oxygen), sugar (carbon, hydrogen, and oxygen).

Compounds and Mixtures A blend of two or more kinds of matter, each of which retains its own identity and properties. Examples: chicken broth, soil, etc.

Back to Early History. . . By 1860 more than 60 elements had been discovered, but there was no real way to organize them. Cannizzaro found a way to compare the atomic masses of each element, using hydrogen as the baseline. Stas calculated the atomic mass of all the known elements and found missing blanks.

Dobereiner: Law of Triads: if you grouped the elements that had similar chemical properties, and the atomic mass of the lighter is added to the heavier, then the average was the mass of the middle one: Ca   Sr   Ba      Average: (40 + 137) ÷ 2 = 88 40    88   137 Li   Na  K         7     23     39           Cl   Br   I 35    80   127

Newlands Found that properties of elements repeated every 8th position or element Law of octaves This idea failed after calcium H ? ? ? ? ? ? Li Be B C N O F Na Mg Al Si P S Cl K Ca

Mendeleev Russian Tried to organize the elements by atomic mass and similar properties Wrote the name and properties of each element on a card and tried to organize them using different patterns

Mendeleev H Li Na K Be Mg Ca B Al ? Predicted Ga C Si ? Predicted Ge Noticed a repeating pattern: H Li Na K Be Mg Ca B Al ? Predicted Ga C Si ? Predicted Ge N P As O S Se F Cl Br

Mendeleev’s 1st Periodic Table

What do you notice about this table? How is this similar to and different from our modern periodic table?

Meyer redid the chart with 60 elements written left to right by mass.

The Modern Periodic Chart 1910 Moseley Discovered that elements had an atomic number (or proton number) Did this by comparing the wavelengths of each X-ray, may by removing the innermost electron from a metal’s nucleus and allowing it to fall back in. More protons, more energy, shorter wavelength X-ray. Found that elements go up on the existing chart by a proton at a time. This order was consistent with Mendeleev’s ordering by property, not strictly atomic mass.

Various Forms of the Periodic Table http://www.nytimes.com/imagepages/2006/10/23/science/20061024_ILLO_GRAPHIC.html

Structure of the Periodic Table Groups or Families (IUPAC convention) Periods (or Series)

Structure of the Periodic Table Metals – 85% : good conductors of heat/electricity Non-metals – 15% Metalloids: has some characteristics of metals and some characteristics of non-metals Noble gases: inert gases Active nonmetals: poor conductors of heat/electricity

Structure of the Periodic Table Periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers. Groups (families) tend to share similar properties

s Block: contains the most reactive metals

p Block: contains metalloids, reactive nonmetals, and noble gases

d Block: transition metals (lose their “s” electrons first)

f Block: holds the rare earth metals (lanthanide and actinide series)

Alkali Metals: Group 1. Have one weakly held outer “s” sublevel electron and tend to lose that electron to become a +1 ion. Ex. Na1+

Alkaline Earth Metals: Group 2 Alkaline Earth Metals: Group 2. Have two outer “s” sublevel electron and tend to lose those electrons to become a +2 ion. Ex. Ca2+

Nitrogen Family: Group 15 Nitrogen Family: Group 15. Has 5 outer “s” and “p” electrons but will gain 3 electrons to complete the octet and become a -3 ion. Losing all 5 electrons (+5 ion) is a less desirable option. Ex. P3-

Chalcogen Family: Has 6 outer “s” and “p” electrons and prefers to gain 2 electrons and become a -2 ion. Ex. O2-

Halogen Family: Has 7 outer electrons and desperately wants one electron to fulfill a complete octet and become a -1 ion. Ex. Cl1-

Noble Gases: Have 8 outer “s” and “p” electron forming a complete octet. They desire to be antisocial – and unreactive. Ex. Ar