Periodic table - Chemistry - General Test Preparation for CUET

Periodic table

• Tabular representation of chemical elements is known as periodic table.
• These chemical elements are arranged according to their properties.
• The chemical elements which have similar properties or similar chemical behaviour are found near to each other in this tabular representation. 

MANDELEEVS PERIODIC LAW (1869)

• The physical and chemical properties of an element are a periodic function of their atomic weight, i.e , when the element are arranged in order of their increasing atomic weight elements with similar properties are repeated after certain regular intervals.

Modern periodic law

• The physical an chemical properties of an element are a periodic function of their atomic Number i.e when the element is arranged in order in order of their increasing atomic weight, elements with similar properties are repeated after certain regular intervals.

Main features of modern periodic table

• it has 7 horizontal rows called periods and 16 vertical columns called groups or families.
• The first period is the shortest period consists of 2 elements.
• The second and third period contain 8 elements, fourth and fifth period contains 18 elements sixth period contains 36 elements and seventh period is incomplete with 29 known elements.
• The elements of second period are known as bridge elements.
• The elements of 18 groups are known as inert gases and noble gases.
• The element of 3 groups to 13 groups is known as transition elements because their properties lie between the properties of the reactive metals.
• The series of elements with z = 58 to z = 71 which occur in the periodic table after lanthanum are called lanthanides or lanthanides.
• The series with the z = 90 to z = 103 which occur in the periodic table after actinium are called actinides or actinides

Classification 

• Groups
• Periods
• Blocks

Groups

• A group is a vertical column in the chemical periodic table.
• In most of groups, the elements have similar characteristics or properties and exhibit a clear trend in properties or characteristics down the group. 

Periods

• A period is known as a horizontal row in the chemical periodic table.
• Mostly groups are the most common way of classifying chemical elements; there are some other regions of the chemical periodic table where the horizontal trends and similarities in properties and characteristics are more significant than vertical group trends.
• This can be true in the d-block or transition metals and especially for the f-block, where the actinides and lanthanides form two substantial horizontal series of elements. 

S-block elements;-

• Elements in which the last electron enters the s-orbital general configuration is ns^(1-2) the elements of 1 and 2 groups are s-blocked elements.
• Properties;-
• They are metals with low melting and boiling point.
• They have low ionization energies and high electropositive.
• Their metallic character and reactivity increase in a group.
• They lose the valance electrons readily to form +1 and +2 ions.
• They are strong reducing agents.
• They are good conductor of heat and electricity.

P-block elements;-

• Elements in which the last electron enters any one of the three p-orbital.
• General configuration is ns⁽²⁾ np^(1-6) the 13 and 18 groups have p-block elements.
• The element of 17 groups is known as halogens and that of 16 group are known as chalcogens.                   
• Properties;-
• The metallic character increases within a group decreases along a period.
• Their ionization energies are relatively higher than than of s-block elements.
• They show more than on oxidation states.
• Their oxidizing character increase in a period and reducing character increases along a group.

D-block elements

• Element in which the last electron enters any one of the five d-orbital.
• General configuration is ( n-1 ) d^(1-10) ns^(0-2).
•  The element of group 3 and 13 belongs to this category.
• They are called as transition elements.
• Properties;-
• They are hard malleable and ductile metal with high m.p and b.p.
• They are good conductor of heat and electricity.
• Their ionization energies are between s and p block elements.
• Their compounds are generally colored.
• They show various oxidation states.
• They form both ionic and covalent compound.
• Most of the transition elements form alloys.

F- block elements

• Element in which the last electron enters any one of the seven f-orbital.
• General configuration is (n-2) f ^(0-14)   (n-1) d^(0-1) ns⁽²⁾.
• There is 28 f-block elements in all.
• They are called inner transition elements.
• Properties
• They are heavy metal with high m.p and b.p.
• They show various oxidation states.
• Their compounds are greenery colored.
• They have high ten dent to form complexes.
• Most of the elements of the actinide series are radioactive.