Explore the Periodic Table and Families of Elements

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The History of the development of a systematic pattern for the elements includes the work of a number of scientists such as John Newlands, who in 1863 proposed the idea of repeating occurances of properties.Dmitri Mendeleev in 1869 proposed a table containing seventeen columns and is usually given credit for the first periodic table since he arranged elements in groups according to their atomic weights and properties. In a revision of his table in 1871 he arranged some elements and proposed a table of eight columns, obtained by splitting each of the long periods into a period of seven elements, an eighth group containing the three central elements (such as Fe, Co, Ni), and a second period of seven elements. The first and second periods of seven were later distinguished by use of the letters a and b attached to the group symbols, which are Roman numerals. This nomenclature of periods (Ia, IIa, etc.) appears slightly revised in the present periodic tables, even in the extended form. It is interesting to note that Lothar Meyer proposed a similar arrangement about the same time.

Mendeleev's table had the elements arranged by atomic weights with recurring properties in a periodic manner. Where atomic weight placement disagreed with the properties that should occur in a particular spot in the table, he gave preference to the element with the correct properties. He even predicted elements for places that were not yet occupied in the table. These predictions proved to be amazingly accurate.

The Structure of the Table The horizontal rows of the periodic chart are called periods or rows. There are seven periods, each of which begins with an atom having only one valence electron and ends with a complete outer shell structure of an inert gas. The first three periods are short periods consisting of 2, 8, and 8 elements respectively. Periods 4 and 5 are long periods of 18 each, while period 6 has 32 elements, and period 7 is incomplete with only 17 elements most of which are radioactive and do not occur in nature.

Metals are found on the left side of the table with the most active metal in the lower left corner. Nonmetals are found on the right side with the most active nonmetal in the upper right hand corner of the chart. The noble or inert gasses are on the far right. Since the most active metals react with water to form bases, the Group I metals are called alkali metals. As you proceed to the right, the base-forming property decreases and the acid forming properties increase. The metals in the first two groups are the light metals, and those toward the center are called heavy metals. The elements found along the dark line in the periodic table are called metalloids. They are the elements which have certain characteristics of metals and other characteristics of nonmetals. Some examples of metalloids are boron, silicon, arsenic, and tellurium.

FAMILIES OF ELEMENTS

With so many elements, it is impractical to being a study of each one individually. The elements here will first be classified generally as metals and nonmetals. Metals will be further divided into alkali and alkaline earth metals. Metalloids will be discussed as elements with intermediate properties or metals and nonmetals, with metals on the left side of the periodic table and metals on the right. Two special classes of elements with special properties discussed are noble gasses, which combine with almost no other elements, and rare-earth elements that are so similar to one another that they are extremely difficult to separate.

Alkali Metals are the elements in Group IA of the periodic table. The members of the family are lithium, sodium, potassium, rubidium, cesium, and francium. All six elements have the properties of metals except they are softer and less dense. They can be cut with a knife. They are the most reactive metals. They are so reactive that they are never found in nature. They are always combined with other elements. The alkali metals have only one electron in their outermost shell, so alkali metals form positive ions.

Alkaline Earth Metals are beryllium, magnesium, calcium, strontium, barium, and radium. These elements, which are harder and more dense than the alkali metals, also have higher melting points and boiling points. They are highly reactive, but not as active as the alkali metals. Like the alkali metals, the alkaline metals are never found free in nature. The alkaline earth metals have two electrons in their outermost energy level, so they also form positive ions.

Transition Metals have properties similiar to one another and to other metals, but their properties do not fit in with those of any other family. Most transition metals are excellent conductors of heat and electricity. Most have high melting points and are hard. Transition metals are much less active than the alkali and alkaline earth metals. Many transition metals combine chemically with oxygen to form compounds called oxides. Many transition metals have more than one oxidation number. Transition metals form compounds that are brightly colored.

From Metals to Non-Metals in groups IIIA to VIA of the periodic table elements have properties which change from metallic to nonmetallic. These groups include the boron family, carbon family, nitrogen family, and oxygen family.

Boron, the first element in the boron family is a metalloid. Aluminum, which is right beneath boron, is by its position a metalloid. But the properties of aluminum are usually those of metals. The other members of the boron family ...gallium, indium, and thallium, are metals. Boron, which is hard and brittle, is never found in nature in the free state. It is usually found combined with oxygen. The compound boric oxide is important in making heat-resistant glass. Boric acid is commonly used as eyewash and antiseptic. The compound borax is useful as a cleaning agent and water softener.

Aluminum is the most abundant metal and the third most abundant element in the earth's crust. Aluminum is found as aluminum oxide in the ore called bauxite. Aluminum is extremely valuable in industry. It is light, strong, and does not tarnish in air. It is a good conductor and is used in wiring, airplane parts, household items.

The Carbon family includes the elements carbon, silicon, germanium, tin, and lead. Carbon can combine with other elements in a great variety of ways. Millions of carbon compounds called "organic compounds." Carbon is called the basis for life because all living things contain organic compounds.

Silicon is the second most abundant element in the earth's crust. Silicon is used in glass and incement. It is also used in solar cells. Solar cells convert the energy of sunlight into electric energy.

Germanium is a metalloid used in transistors. Transistors are devices found in many electronic instruments, such as radios and televisions. Tin is a metal which resists rusting and corrosion. The most dense element in the carbon family is the metal lead.Lead forms poisonous compounds.

The Nitrogen family consists of nitrogen, phosphorus, arsenic, antimony, and bismuth. Nitrogen and phosphorus are nonmetals. Arsenic is a metalloid with mostly nonmetallic properties. Antimony is a metalloid with mostly metallic properties. Bismuth is the most metallic element in the family. All members of the nitrogen family have five electrons in their outermost energy level. These elements lose electrons easily.

The Oxygen family includes oxygen, sulfur, selenium, tellurium, and polonium. All of these have six electrons in their outermost energy level. Their properties go from nonmetallic in oxygen and sulfur to metalloid in selenium and tellurium to metallic in polonium.

Halogens are the elements in family VIIA. They are strongly nonmetallic. The halogens include fluorine, chlorine, bromine, iodine, and astatine. They are the most active nonmetals. The chemical reactivity of the halogens is due to the number of electrons in the outermost energy levels of their atoms. Fluorine is the most active halogen. They have low melting points and boiling points. In the gas phase they exist as diatomic elements. Halongens combine readily with metals to form a class of compounds known as salts.

Noble Gasses are colorless gasses that are extremely unreactive. Because do not readily combine with other elements to form compounds, the noble gasses are called inert. The family of noble gasses includes helium, neon, argon, krypton, xenon, and radon. All the noble gasses are found in small amounts in the earth's atomsphere. One important property of the noble gasses is their inactivity. They are inactive because their outermost energy level is full.