58Ce to,71Lu possess almost the same properties as,, La. So, the name lanthanoids is the most appropriate one for these elements.
7th period is incomplete and contains 2 elements from s-block (7s) 14 elements from f-block (51), 10 elements from d-block (6d) and some elements from p-block (7p). The 5f elements are called Actinoids or as Actinides. They are from 90Th to 103Lr.
The f-block elements known as lanthanoids and actinoids are shown separately at the bottom of the periodic table.
Metals and Non metals
You have learnt about the properties of metals in the chapter Metals and Non Metals in class VIII. Let us study the metallic properties elements in periodic table.
The elements with three or less electrons in the outer shell are considered to be metals and those with five or more electrons in the outer shell are considered to be non metals. We may find some exceptions to this. 'd' block elements (3rd group to 12th group) are metals and they are also known as transition metals and the metallic character of d-block elements decreases gradually from left to right in periodic table. Lanthanoids and actinoids actually belong to 3 group (III B) which is within the transition elements: hence they are called the inner transition elements.
Metalloids or semi-metals are elements which have properties that are intermediate between the properties of metals and non metals. They possess properties like metals but brittle like non metals. They are generally semi conductors. Eg: B, Si, As, Ge.
All elements in s-block are metals, whereas in p-block (except 18th group) there are metals, non metals and metalloids. In periodic table you will notice a staircase like demarcation. The elements to the left of this demarcation are metals and to the right are non-metals. The elements on staircase (or) very near to it like B, Si, As, Ge etc., are metalloids.
Periodic properties of the elements in the modern table
The modern periodic table is organized on the basis of the electronic configuration of the atoms of elements. Physical and chemical properties of elements are related to their electronic configurations particularly the outer shell configurations. The atoms of the elements in a group possess
