Elements within the same group have the same number of valence electrons. The number of valence electrons in an element determines whether the element is a metal or nonmetal and strongly influences the way in which an atom of that element reacts. In other words, valence electrons determine the chemical properties of an element. When an atom reacts, it tends to become stable by gaining, losing, or sharing electrons with other atoms, seeking a full valence shell. An atom with a full valence shell has the same electron configuration as that of the noble gas nearest to it on the periodic table.
Group 1, on the far left column of the periodic table, contains elements known as the alkali metals, which are the most reactive of the metals.These elements are highly reactive because they have one valence electron, which they tend to lose very easily. For example, sodium, with atomic number 11, tends to lose one electron seeking the same electron configuration as neon, a noble gas with 2 electrons in the first energy level and a full valence shell with 8 electrons in the second, outermost, energy level.
Group 2, the second group from the left, is known as the alkaline earth metals. Group 2 elements have 2 valence electrons, which they also tend to lose, but not as readily as the elements in group 1. As a result, group 2 metals are less reactive than group 1 metals. For example, calcium—a group 2 metal—has to be heated before it reacts with oxygen. However, potassium—which is a group 1 metal right next to calcium on the periodic table—reacts readily with oxygen when left open to the air.
Groups 3 to 12—the columns in the middle of the table—are known as the transition metals. The lanthanides and actinides, shown at the bottom, are also transition metals. Many transition metals are less reactive than group 1 or group 2 metals and can lose a variable number of electrons to become stable. An example of a transition metal is copper. Unlike calcium and potassium, copper reacts very slowly with oxygen. In addition to the above types of metals, other metals, such as Aluminum (Al), react with oxygen to form a protective coating that seals the metal off from further reaction.
Two other important groups to note are the halogens (such as fluorine and chlorine) in group 17 and the noble gases (such as helium and neon) in group 18. Both groups are located on the far right in the nonmetals section of the table. The halogens are the most reactive of the nonmetals. Each of these elements is missing one electron in their valence shell to acquire noble gas configuration. Therefore, halogens are highly reactive and tend to easily gain one electron from other atoms. In contrast, the noble gases in group 18 have a full set of valence electrons. As a result, the noble gases are almost completely non-reactive; they are essentially inert and do not lose or gain electrons easilNext part
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