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Thursday, 1 August 2013

Modern Periodic Law - Education through Web and Mobile Media in Pakistan - ProPakistanis

          After the discovery of atomic number by Moseley in 1913, it was noticed ghat elements could be classified more satisfactorily by using their atomic numbers rather than their atomic masses. This improvement rectified a number of confusions presented in the old Periodic Table. The Modern Periodic Law states That: If the elements are arranged in ascending order to their atomic numbers, their chemical properties repeat in a periodic manner.

Essential features of Periods:
§  Elements with similar properties are placed in vertical columns called Groups. There are eight groups, which are usually numbered by Roman numerals I to VIII. Each group is divided into two sub-groups, designated as A and B sub-groups
§  There are 7 periods in the Periodic table numbered by Arabic numerals 1 to 7
§  The Period 1 contains only two elements, hydrogen and helium.
§  The periods 2 and 3 contain eight elements each and are called short periods.
§  The periods 4 and 5 are called long periods. Each long period consists of eighteen elements. Out of these, eight are typical elements belonging to A subgroup, whereas the other ten elements placed in the centre of the table belong to B subgroups are known as transition Elements.
§  The period 6 is also a long period, which contains thirty two elements. In this period there are eight typical elements, ten transition elements and a new set of fourteen elements called Lanthanides as they start from La.
§  The Period 7 is incomplete so far. It contains only two normal elements 87 Fr and 88Ra, ten transition elements and fourteen inner transition elements. The transition elements of this period are called Actinides, as they follow 89 Ac.
§  The inner transition elements are shown at the bottom of the Periodic Table under Lanthandies. Due to their scarcity, the inner transition elements are also called “rare earth elements”.
Alkali metals:
Elements of the group IA are called Alkali Metals because of their property to form strong alkalies with water.
Alkaline earth metals:
Due to their presence in Earth’s crust and alkaline character, the elements of group IIA are known as Alkaline Earth Metals.
The name Halogens is given to the elements of group VIIA due to their salt forming property.
Nobal gases:
As the gases of group VIIIA are least reactive they are called Noble Gases.
s-block elements:
Elements of IA and IIA sub-groups are called s-block element because their valence electrons are available in s orbital.
p-block elements:
The elements of IIIA to VIIIA subgroups (except He) are known as p-block elements as their valence electrons are present in p orbital.
d-block elements:
In transition elements, electrons in d orbital are responsible for their valencyhence, they are called d-block elements.
f-block elements:
In lanthanides and Actinides valence electrons are present in f orbital hence, these elements are called f-block elements.
Chemically all the elements which have a tendency to form positive ions by losing electrons are considered metals.
All the metals are good conductor of heat and electricity. A characteristic property of metals is that they form basic oxides, which give bases when dissolved in water.
The elements which gain electrons and form negative ions are called non-metals. All the gases are non-metals.
The non-metals are usually poor conductor of heat and electricity. Non-metals form acidic oxides, which yield acids on dissolving in water.
Semi Metals or metalloids:
Some elements, especially lower members of groups, IIIA, IVA and VA have properties of both metals as well as non-metals.

These elements are called semi-metals or metalloids.
The oxides of these elements are called amphoteric oxides, which have characteristic of both acidic and basic oxides.

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