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In 1869 a Russian chemist named Dmitri Mendeleev (1834-1907) achieved the first major breakthrough in organizing the chemical elements. He realized that if elements were arranged in vertical columns by order of increasing atomic mass, there was a regular, or periodic, reoccurring sequence of similar chemical and physical properties. Next, Mendeleev established an even greater degree of organization in his table by arranging the columns so that elements with similar chemical and physical properties were adjacent to each other.
In addition to establishing a successful preliminary method of organizing the elements, Mendeleev had left blank spaces. He predicted that the blank spaces in his table would predict the existence of as yet undiscovered elements with certain physical and chemical properties. Amazingly, elements with these predicted properties were eventually discovered.
| Legend | |
|---|---|
| Metals | A solid substance that is a good conductor of heat and electricity. Can be formed into many shapes. |
| Metalloid | "Middle elements" - conduct heat and electricity better than nonmetals, but not as well as metals. Easier to shape than nonmetals, but not as easy as metals. Solid at room temperature. |
| Nonmetals | A poor conductor of heat and electricity. Not easily formed into shapes. |
The periodic table arranges all the known elements in an informative array. Elements are arranged left to right and top to bottom in order of increasing atomic number. This order generally coincides with increasing atomic mass.
The different rows of elements are called periods. The period number of an element signifies the highest energy level an electron in that element occupies (in the unexcited state). The number of elements in a period increases as one traverses down the periodic table because as the energy level of the atom increases, the number of energy sub-levels per energy level increases.
Using the data in the table scientists, students, and others can extract information concerning individual elements. For instance, you can use carbon's atomic mass mass to determine how many carbon atoms there are in a 1 kilogram block of carbon.
You also gain information from the periodic table by looking at how it is put together. By examining an element's position on the periodic table, one can infer the electron configuration. Elements that lie in the same column on the periodic table (called a "group") have identical valance electron configurations and consequently behave in a similar way chemically. For instance, all the group 18 elements are inert gases.
Elements with atomic numbers up to 92 (uranium) occur naturally on Earth. Those with atomic numbers 93 (neptunium) or greater are artificial. They have to be synthesized, or created by combining two or more elements with lower atomic numbers. Element 100 is named fermium. Elements with atomic numbers 101 and onwards are known as the transfermium elements. They are also known as heavy elements because their atoms have very large masses compared with atoms of hydrogen, the lightest of all elements.
The heaviest element synthesized to date is element 112. One atom of this element was synthesized by scientists at the Heavy-Ion Research Center (Gesellschaft für Schwerionenforschung [GSI]) in Darmstadt, Germany, in February 1996. It was made by bombarding the element lead (atomic number 82) with a high-energy beam of atoms of the element zinc (atomic number 30). The atom existed for a fraction of a second before splitting up. Elements 110 and 111 were discovered by the same group of scientists in 1994.
Names for the six new heavy elements were approved on August 31, 1997, by the International Union of Pure and Applied Chemistry (IUPAC) in Geneva. Elements 110, 111, and 112 have not yet been named.
