Characteristics of periods and groups of a periodic table | مصادر الكيمياء

Characteristics of periods and groups of a periodic table

 

 

Characteristics of periods and groups of a periodic table

Characteristics of periods

1 –  Valence electrons. On moving from left to right in a period, the number of valence electrons increases from 1 to 8 (except first period where the increase is from one to two only).

  Na         Mg         Al          Si            P           S           Cl          Ar

2,8,1      2,8,2      2,8,3      2,8,4      2,8,5      2,8,6      2,8,7      2,8,8

2 –  Valency. On moving from left to right in each short period, the valency of elements increases from 1 to 4 and then decreases to 0.

  Na         Mg         Al          Si            P           S           Cl          Ar

1            2           3           4             3           2            1          0

3 –  At the end of each period is the zero group clement, the inert gas.

4 –  Atomic radii of the element decreases gradually due to increase in nuclear charge of atoms on going from left to right in a period.

5 –  On moving from left to right in a period the metallic character of elements decreases.

6 –  On moving from left to right in a period, the chemical reactivity of elements first decreases and then increases.

7 –  On moving from left to right in a period, the basic nature of oxides decreases and the acidic nature of oxides increases.

Characteristics of groups

The vertical column in the periodic table is called a group.

1 – All the elements of a group have the same number of valence electrons, for example all group 7 elements have 7 valence electrons each in their atoms.

2 – In a group all the elements have the same valency. For example, group 1 elements : Li, Na, K etc. have a valency of +1. Elements of group 17 : Cl, Br, I etc. have valency of -1.

3 –  On going down in a group of the periodic table the size of atoms increases.

4 –  On going down in a group the metallic character incre­ases.  For example, groups 14 and 15 begins with carbon, and nitrogen which are non-metals. These groups ends with metals lead and bismuth respectively which are metals; The oxides of the metals become increasingly basic.

5 –  Melting point and boiling point decreases on going down a group.

6 –  Ionization energy decreases on going down a group with increase in atomic number. This is because the size off the atom increases and the valence electrons are further removed from the attractive effect of the nucleus.

 

 

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