Periodic Classification Of Elements
Very Short Answer Type Questions
Q.1.  What were the limitations of dobereiner's classification ?
Ans. (i) The classification of known elements could not be possible on the basis of Dobereins's traids. (ii) Dobereiner could from only three traids from the elements known at that time.

Q.2. An atom has electronic configuration 2,8,7,
(a) What is the atomic number of this element ? (b) To which of the following elements would it be chemically similar ? (Atomic numbers are given in parentheses.
N(7),F(9),P(15),Ar(18)
Ans. (a) The atomic number of element is 17.
(b) It will be chemically similar to F(9) because the electronic configuration of F(9) is 2, 7 i.e., both have electrons in their outermost orbit.

Q.3. What are valence electrons ? 
Ans. The electron present in the outermost orbit of an atom are called valence electron.

Q.4. Write names of elements of zero group.
Ans. Helium, Neon, Argon, Krypton, Xenon, Radon.

Q.5. Write the following halogen inthe increasing order of their reactivity Br, I, Cl, F.
Ans. I <Br <Cl < F.

Q.6. What are periods ? 
Ans. The horizontal rows of periodic table are called periods. 


Short Answer Type Questions
Q.1.  Use Mendeleev's periodic table to predict the formula for the oxides of the following elements:
                       K,C,Al,Si,Ba.
Ans.Element K : formula of its oxide is K2O
Element C : formula of its oxide is CO2
Element Al : formula of its oxide is Al2O3
Element Si : formula of its oxide is SiO2
Element Ba : formula of its oxide is BaO.

Q.2. By considering their position in the periodic table, which one of the following elements would you expect to have maximum metallic characteristics:
              Ga,Ge,As,Se,Be.
Ans. Ge and As are metalloids or semi-metals. Only Be and Ga are metals. Be is placed in second group while Ga is placed in 13th group. So, be have maximum metallic characteristics.

Long Answer Type Questions
Q.1. Compare and contrast the arrangement of elements in Mendeleev's periodic table. 
Ans. (i) In Mendeleev's periodic table 63 elements were given place while in modern periodic table 118 elements are given place.
(ii) Mendeleev left some gaps in his periodic table while in modern periodic table all elements are well arranged.
(iii) Mendeleev's periodic table is based on atomic masses of the elements while the modern periodic table is based on atomic number of elements.