Which two criteria did Mendeleev use to classify the elements in his periodic table? (b) State Mendeleev’s periodic law. (c) Why could no fixed position be given to hydrogen in Mendeleev’s periodic table? (d) How and why does the atomic size vary as y
Answers
(b)Properties of elements are a periodic function of their atomic masses.
(c)Because it can be placed in both Group no. 1 and 17.
Answer: a) The 2 criteria used by Mendeleev were-
i) increasing order of atomic masses of elements
ii. Similarities in formulas of oxides and hydrides formed by the elements. The formulas helped in predicting properties.
b) Mendeleev's periodic law stated that " properties of elements are a periodic function of their atomic masses."
C) hydrogen resembles both alkali metals and halogens. It forms positive ion like alkali metals as well as negative ion like halogens. Hence it can be placed in group 1 or 17. Thus position of hydrogen could not be fixed.
D) Atomic size varies both ways- 1) across a period ( due to increase in nuclear charge over the same number of shells) and 2) down the group ( due the addition of shells in the atoms as one moves down the group).
Explanation: