Interactive Periodic Table of the Elements, in Pictures and Words © 2005-2016 Keith Enevoldsen elements.wlonk.com

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Learning Objectives

Know the classification of the different elements. Define valence electrons. Describe how the number of valence electrons are related the arrangement of the main group elements and its positiveeast.orgical behavior.

Elements that have similar positiveeast.orgical properties are grouped in columns called groups (or families). As well as being numbered, some of these groups have names—for example, alkali metals (the first column of elements), alkaline earth metals (the second column of elements), halogens (the next-to-last column of elements), and noble gases (the last column of elements). In and atomic , the main group is the group of elements whose lightest members are represented by , , , , , , , and as arranged in the of the elements. The main group includes the elements (other than , which is sometimes not included) in groups 1 and 2, and groups 13 to 18. Main-group elements (with some of the lighter ) are the most abundant elements on , in ns , and in ns . They are sometimes also called the representative elements. In older nomenclature the main-group elements are groups IA and IIA, and groups IIIB to 0 (CAS groups IIIA to VIIIA). Group 12 is labelled as group IIB in both systems. Group 3 is labelled as group IIIA in the older nomenclature (CAS group IIIB).

Each row of elements on the periodic table is called a period. Periods have different lengths; the first period has only 2 elements (hydrogen and helium), while the second and third periods have 8 elements each. The fourth and fifth periods have 18 elements each, and later periods are so long that a segment from each is removed and placed beneath the main body of the table.

One way to categorize the elements of the periodic table is shown in Figure (PageIndex1). The first two columns on the left and the last six columns on the right as mentioned earlier are the main group elements. The ten-column block between these columns contains the transition metals. The two rows beneath the main body of the periodic table contain the inner transition metals. The elements in these two rows are also referred to as, respectively, the lanthanide metals and the actinide metals.

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Example (PageIndex2)

Based on its position in the periodic table, classify each element below as metal, a nonmetal, or a metalloid.

Se Mg Ge

Solution

In Figure (PageIndex1), selenium lies above and to the right of the diagonal line marking the boundary between metals and nonmetals, so it should be a nonmetal. Magnesium lies to the left of the diagonal line marking the boundary between metals and nonmetals, so it should be a metal. Germanium lies within the diagonal line marking the boundary between metals and nonmetals, so it should be a metalloid.

Exercise (PageIndex2)

Based on its location in the periodic table, do you expect indium to be a nonmetal, a metal, or a metalloid?

Answer Indium is a metal.

Example (PageIndex3): Classification of Elements

Classify each element as metal, non metal, transition metal or inner transition metal.

Li Ar Am Fe

Solution

Lithium is a metal. Argon is a non metal Americium is an inner transition metal Iron is a transition metal.

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Summary

Valence electrons are the outer-shell electrons of an atom. These are electrons that can participate in the formation of a positiveeast.orgical bond. Elements that exhibit similar positiveeast.orgistry appear in vertical columns called groups (numbered 1–18 from left to right). The seven horizontal rows are called periods. Some of the groups have widely-used common names, including the alkali metals (Group 1) and the alkaline earth metals (Group 2) on the far left, and the halogens (Group 17) and the noble gases (Group 18) on the far right. An important grouping of elements in the periodic table are the main group elements, the transition metals, and the inner transition metals (the lanthanides, and the actinides). The elements can be broadly divided into metals, nonmetals, and semi metals. Semi metals exhibit properties intermediate between those of metals and nonmetals. Metals are located on the left of the periodic table, and nonmetals are located on the upper right. They are separated by a diagonal band of semi metals. Metals are lustrous, good conductors of electricity, and readily shaped (they are ductile and malleable). Solid nonmetals are generally brittle and poor electrical conductors.