Types of elements

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1. Main Group Elements

The elements present in groups 1 and 2 on left side and groups 13 to 17 on the right side of the periodic table are called representative or main group elements. Their outermost shells are incomplete, which means their outermost shell has less than eight electrons.

2. Noble Gases

Group 18 on the extreme right side of the periodic table contains noble gases. Their outermost shells contain 8 electrons except He which contains only 2 electrons.

Their main characteristics are :
(a) They have 8 electrons in their outermost shell (except He which has 2 electrons).
(b) Their combining capacity or valency is zero.
(c) They do not react, and so are almost inert.
(d) All the members are gases.

3. Transition Elements

The middle block of periodic table (groups 3 to 12). These elements represent a transition (change) from the most electropositive element to the most electronegative element, so they are named as transition elements.

Their important characteristics are as follows :
(a) All these elements are metals and have high melting and boiling points.
(b) They are good conductors of heat and electricity.
(c) Some of these elements get attracted towards magnet.
(d) Most of these elements are used as catalysts.
(e) They exhibit variable valencies.

4. Inner Transition Elements

These elements, also called rare-earth elements, are shown separately below the main periodic table. These are two series of 14 elements each.
(a) The first series called lanthanoids, which consists of elements from 58 to 71 (Ce to Lu). They all are placed along with the element 57, lanthanum (La) in the same position (group 3, period 6) because of very close resemblance between them. It is only for the sake of convenience that they are shown separately below the main periodic table.
(b) The second series of 14 rare-earth elements is called Actinoids. It consists of elements from 90 to 103 (Th to Lr), and they are all placed along with the element 89, actinium (Ac) in the same position (group 3, period 7), but for convenience, they are shown below the main periodic table. In all rare-earths (lanthanoids and actinoids), three outermost shells are incomplete. They are therefore called inner transition elements. It is interesting to note that the element lanthanum is not a lanthanoid, and the element actinium is not an Actinoid.

5. Metals

Metals are present in the left portions of the periodic table. The strong metallic elements; alkali metals (Li, Na, K, Rb, Cs, Fr); and alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra) occupy group 1 and 2, respectively.

6. Non-metals

Non-metals occupy the right hands portion of the periodic table. Strong non-metallic elemets, i.e., halogens (F, Cl, Br, I, At) and chalkogens (O, S,Se, Te, Po) occupy group 17 and 16, respectively.

7. Metalloids

Metalloids are the elements that show mixed properties of both metals and non-metals. They are present along the diagonal line starting from group 13 (Boron) and going down to group 16 (Polonium).

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