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  The periodic trend in the metallic character of elements is clearly understood from their position is the modern periodic table. Let us first consider the metallic character of elements belonging to the same group. While going down a group a new shell gets added, resulting in an increase in the distance between the nucleus and the valence electrons. This results in lowering the effective nuclear charge and thereby lowering the attractive force on the valence electrons. As a result of this the tendency of the atom to lose electrons increases. Also the penultimate shell becomes the outermost shell on losing valence electrons. The penultimate shell is a complete octet. Therefore, the resulting cation has a special stability. Due to this, the tendency of the atom to lose electrons increases further. The metallic character of an atom is its tendancy to lose electrons. Therefore, the following trend is observed : The metallic character of elements increases while going down the group.
  While going from left to right within a period the outermost shell remains the same. However, the positive charge on the nucleus goes on increasing while the atomic radius goes on decreasing and thus the effective nuclear charge goes on increasing. As a result of this the tendency of atom to lose valenece electrons decreases within a period from left to right (See Table 2.10).
  The two factors namely, the increasing nucleur charge and decreasing atomic radius as we go from left to right within a period, are responsible for increasing the effective nuclear charge. Therefore, the valence electrons are held with greater and greater attractive force. This is called electronegativity of an atom. Due to increasing electronegativity from left to right within a period, the ability of an atom to become anion by accepting outside electrons goes on increasing. The tendency of an element to form anion or the electronegativity is the nonmetallic character of an element.
Use Your Brain Power!27
1. What is the cause of nonmetallic character of elements?
→ The tendency of an element to form (negatively charged) anions, is the cause of nonmetallc characther of elements.
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2. What is the expected trend in the variation of nonmetallic character of elements from left to right in a period?
→ As we move from left to right in a period, the atomic number increases and the size of the atom decreases. This increases the electronegativity and therefore the nonmetallic character increases.
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3. What would be the expected trend in the variation of nonmetallic character of elements down a group?
→ As we move down in a group, the atomic number and the size of the atom increases. This decreases the electronegativity and therefore the nonmetallic character increases.
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Always Remember27
  1. While going downwards in any group the electropositivity of elements goes on increasing while their electronegativity goes on decreasing.
  2. While going from left to right in any period the electronegativity of elements goes on increasing while their electropositivity goes on decreasing.
  3. Larger the electropositivity or electronegativity of the element higher the reactivity.
Gradation in Halogen Family27
The group 17 contains the members of the halogen family. All of them have the general formula X2. A gradation is observed in their physical state down the group. Thus, fluorine (F2) and chlorine (Cl2) are gases, bromine (Br2) is a liquid while iodine (I2) is a solid.

This page was last modified on
04 May 2020 at 19:22

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