Metallic & nonmetallic property , Acidic & basic property in the periodic table
At the beginning of the nineteenth century Berzelius was the first scientist who classified elements into two main group ( metals and nonmetals ) , according to their physical properties , Indeed that was before knowing anything about atomic structure , This is an old classification which is still currently in use , although there are no boundaries between them and their properties in the periodic table .
They are good electric conductors , due to the mobility of their few valence electrons , which can transfer from one position to another in the metal structure .
They have small atomic radius which leads to high values for ionization energy and electron affinity , They are electronegative elements , due to their tendency to gain electrons to form negative ions that have the same electron structure of the nearest noble gas .
The metalloids are characterized by the following properties :
They have the metallic appearance and the most properties of nonmetals , Their electronegativity is intermediate between metals and nonmetals , Their electric conductivity is less than that of metals , but more than that of nonmetals , They are used in manufacturing electronic instruments parts – such as transistors – as they are semiconductors .
Metalloids are a group of elements that has a metallic appearance and most of the properties of nonmetals which characterized by their electronegativity is intermediate between metals and nonmetals and their electric conductivity is less than that of metals , but more than that of nonmetals .
The graduation of metallic and nonmetallic property in the periodic table :
In the same group : The metallic character increases ( The nonmetallic character decreases ) with the increase in the atomic number as we go down the group , due to their large atomic radius and the low ionization potential and electron affinity .
In the same period : The period begins by the strongest metals in group 1A , then the metallic property decreases gradually by increasing the atomic number across the period till we reach the metalloids , To the right of the metalloids begins the nonmetallic property , The period ends by the elements of the highest nonmetallic property in group 7A .
Consequently : Cesium is considered the most active metal , because the metallic property increases at the same group by increasing the atomic number and it is placed at the bottom of the left hand side the table ( the lowest metal in ionization potential ) .
Fluorine is considered the most active nonmetal , because the nonmetallic property decreases at the same group by increasing the atomic number and it is placed at the top of the right side of the table ( the most electronegative nonmetal ) .
The graduation of metallic and nonmetallic property in the third period , It is clear that by increasing the atomic number , the metallic character decreases and the nonmetallic character increases .
Acidic and basic property
The nonmetallic oxides are named by acidic oxides , because :
They dissolve in water forming oxygenated acids .
CO2 ( g ) + H2O ( l ) → H2CO3 ( aq )
SO3 ( g ) + H2O ( l ) → H2SO4 ( aq )
They react with alkalis forming salt and water .
CO2 ( g ) + 2NaOH ( aq ) → Na2CO3 ( aq ) + H2O ( l )
From the acidic oxides , Carbon dioxide CO2 , Sulphur trioxide SO3 , Nitrogen dioxide NO2 .
The metallic oxides are usually known as basic oxides , Some basic oxides are not soluble in water and others are soluble in water forming alkalis , the water soluble basic oxides are also known as alkali oxides .
K2O ( s ) + H2O ( l ) → 2KOH ( aq )
H2O ( l ) + Na2O ( s ) → 2NaOH ( aq )
From the basic oxides , Potassium oxide K2O , Sodium oxide Na2O , Magnesium oxide MgO .
2HCl ( aq ) + Na2O ( s ) → 2NaCl ( aq ) + H2O ( l )
MgO ( s ) + H2SO4 ( aq )→ MgSO4 ( aq ) + H2O ( l )
ZnO ( s ) + H2SO4 ( aq )→ ZnSO4 ( aq ) + H2O ( l )
ZnO ( s ) + 2NaOH ( aq )→ Na2ZnO2 ( aq ) + H2O ( l )
Amphoteric oxides such as Aluminum oxide Al2O3 , Zinc oxide ZnO , Antimony oxide Sb2O3 , Tin oxide SnO .
The graduation of acidic and basic property in the periodic table :
In the period : The basic property of the oxide decreases as the atomic number of the element increases , while the acidic property increases .
In the group : where in the group which starts by a metal , the basic property of the oxide increases as the atomic number increases as in group 1A .
In the group which starts by a nonmetal , The acidic property of the oxide increases as the atomic number increases as in group 7A .
The graduation of acidic and basic property in the third period , As the atomic number increases the basic property decreases and the acidic property increases .
The acidic property of hydrogen compounds of group 17 ( halogens ) increases as the atomic number increases , Because the increase in the atomic number in the group leads to the increase in the atomic size of halogen and then its attraction force for hydrogen atom decreases , making it easier to be ionized .