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Elements are the building blocks of nature. Chemical elements are the fundamental materials of which all matter is composed. An element is a pure substance that cannot be broken down or reduced further without changing its properties. Water, for example, is a compound composed of two elements: hydrogen and oxygen.

The smallest amount of an element that can exist is an atom. An atom is made up of subatomic particles. The most important of these are

• protons, which have positive electrical charges;
• electrons, which have negative electrical charges;
• neutrons, which are electrically neutral.

The atomic number of an element is the number of protons in one atom of the element. Each element has a different atomic number. For example, the atomic number of hydrogen is 1, and the atomic number of oxygen is 8.

Periodic Table

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, reccurring 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 hypothesised 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.

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 f�r 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.