Classification of elements: the arrangement of elements in such a manner that elements with similar properties are grouped together while elements with dissimilar properties are separated.
(ii)All the elements in a group have same no. of electrons in outermost shell.
(iii)The elements of each group have similar chemical properties due to same valence electrons . (iv)There are in all seven periods.
(v)First three periods with 2,8,8 element called short periods. The next three periods with 18,18,32 element called long period while seventh period is an incomplete period. (vi)The number of elements in these periods are based on filling of electron into various shell on the formula 2n2 (n-number of shell)
Advantages of long form of periodic table:-
1. The position of the elements are linked with their electronic configuration.
2. Position of isotopes of an element is justified since they have same atomic number.
3. Similar properties of element in a group is also justified due to same valence electrons.
4. Each group is an independent group and idea of sub-group discarded.
Elements in group 1 are called alkali metals.
Elements in group 2 are called alkaline earth metals.
Elements in group 17 are called halogens.
Elements in group 18 elements are called inert gases or noble gases.
Significance of group in the periodic table is that an element in a group has same no. of valence electrons, valence and thus identical chemical properties.
1st period – 2 elements and is called very short period.
2nd period – 8 elements and is called short period.
3rd period - 8 elements and is called short period.
4th period – 18 elements and is called long period.
5th period – 18 elements and is called long period.
6th period – 32 elements and is called very long period.
7th period – incomplete period.
Valency: it is defined as the combing capacity of an atom of an element to acquire noble gas configuration. It is equal to the number of electrons lost, gained or shared during the formation of a chemical compound.
Atomic size / Atomic radii: It is defined as the distance from the Centre of nucleus to the outermost shell of the atom. It is generally expressed in Pico meter (Pm).
On moving down the group the group the atomic radii increases.
Across the period the atomic radii decrease.
Oxides and its nature:
Metals react with oxygen to form oxides by loss of electrons. These oxides on dissolution in water form bases.
Reactivity of elements:
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