(i) What are the demerits of Mendeleev's periodic table?
(ii) What is an alloy? Describe any four alloys which are used in daily life
Where are those used?
(iii) If the mass of a planet is eight times the mass of the earth and its radius is
twice the radius of the earth, what will be the escape velocity for that planet
(iv) What are redox reactions? Write any two examples of redox reaction and
explain it with the help of chemical reactions.
Answers
Explanation:
Mendeleev Periodic Table – We all know that there are 118 elements present in our periodic table. Out of these 118 elements, 94 elements are natural elements and 24 elements are synthetic elements. Back in the year 1800, only 30 elements were known. With the discovery of more and more elements, remembering the elements and their properties were burdensome for scientists. They started gathering information about the elements and categorizing it. The categorization of elements in a tabular form according to their properties became popular. The tabular form structure in which various elements are arranged according to their properties is known as the periodic table.
Introduction to Mendeleev Periodic Table
Dmitri Ivanovich Mendeléev, a Russian chemist, was the most important contributor to the early development of the periodic table. Many periodic tables were made but the most important one was the Mendeleev periodic table.
In 1869, after the rejection of Newlands Octave Law, Mendeleev Periodic table came into the picture. In Mendeleev’s periodic table, elements were arranged on the basis of the fundamental property, atomic mass, and chemical properties. During Mendeleev’s work, only 63 elements were known. After studying the properties of every element, Mendeleev found that the properties of elements were related to atomic mass in a periodic way. He arranged the elements such that elements with similar properties fell into the same vertical columns of the periodic table.
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Answer:
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Explanation:
(I) demerits of mendeleevs periodic table
(i) elements in Mendeleev periodic table have not been arranged in the increasing order of their atomic masses for example Cobalt and Nickel even to Copper has the highest atomic mass then nikal it placed before nickel in his table.
(ii) hydrogen forms compounds similar to group 1 in however it also forms similar diatomic molecules is group group 7 elements it could not be assigned a fixed position in the table
(iii) isotope post a challenge to mentally stable for example chlorine has two major isotopes CL 35 and CL 37 hence they can be placed separately in accordance with their masses 35 and 37 m u or both of them could be placed together owning to the similar chemical properties
(II) alloys are the metals were form by mixing two elements due to which alloy gets high resistance .
four alloys which we use in our daily life are bronze brass Steel
(III) -----
(IV)
reaction in which both oxidation process and reduction process take place simultaneously are called redox reactions .