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The rebab.netical behavior of atoms is controlled by their electron configuration. Since the families of elements were organized by their rebab.netical behavior, it is predictable that the individual members of each rebab.netical family will have similar electron configurations.
Families of the Periodic Table
Remember that Mendeleev arranged the periodic table so that elements with the most similar properties were placed in the same group. A group is a vertical column of the periodic table. All of the 1A elements have one valence electron. This is what causes these elements to react in the same ways as the other members of the family. The elements in 1A are all very reactive and form compounds in the same ratios with similar properties with other elements. Because of their similarities in their rebab.netical properties, Mendeleev put these elements into the same group. Group 1A is also known as the alkali metals. Although most metals tend to be very hard, these metals are actually soft and can be easily cut.
Group 2A is also called the alkaline earth metals. Once again, because of their similarities in electron configurations, these elements have similar properties to each other. The same pattern is true of other groups on the periodic table. Remember, Mendeleev arranged the table so that elements with the most similar properties were in the same group on the periodic table.
It is important to recognize a couple of other important groups on the periodic table by their group name. Group 7A (or 17) elements are also called halogens. This group contains very reactive nonmetal elements.
The noble gases are in group 8A. These elements also have similar properties to each other, the most significant property being that they are extremely unreactive, rarely forming compounds. We will learn the reason for this later, when we discuss how compounds form. The elements in this group are also gases at room temperature.
If you can locate an element on the Periodic Table, you can use the element"s position to figure out the energy level of the element"s valence electrons. A period is a horizontal row of elements on the periodic table. For example, the elements sodium ((ceNa)) and magnesium ((ceMg)) are both in period 3. The elements astatine ((ceAt)) and radon ((ceRn)) are both in period 6.
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