Periodic Table History

Early History

• 1800 – 1860– The elements were still confused with compounds

and mixtures

CompoundMixture

Element

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

• 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 = 8840 88 137

• Li Na K 7 23 39

• Cl Br I35 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 FNa Mg Al Si P S ClK 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

Noticed a repeating pattern:

HLi Na KBe Mg CaB Al ? Predicted GaC Si ? Predicted GeN P AsO S SeF 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 TableGroups or Families (IUPAC convention)

Structure of the Periodic Table

1. Metals – 85% : good conductors of heat/electricity

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

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