Question
30, 31, 32, 33, 34, 35
Answers
Explanation:
30. X( largest atomic number) then Y and then Z (smallest atomic number)
going down the atomic size increases as new shell is introduced every time we move down to new period.
31. ans The isotopes of chlorine Cl-35 and Cl-37 should be placed in the same slot because their chemical properties are the same. The two isotopes of chlorine have the same atomic number and chemical properties. We know that the arrangement of elements is made on the basis of atomic number in the periodic table.
32. ans Nitrogen is more electronegative than phosphorus. On moving down a group, the number of shell increases. Therefore, the valence electrons move away from the nucleus and the effective nuclear charge decreases. This causes the decrease in the tendency to attract electron and hence electro negativity decreases.
33. ans Atomic size increases as we go down a group because each time one new shell is added and electrons in the outermost shell move away from the nucleus.
34. The system of classification of elements into triads was not found suitable because it failed to arrange all the then known elements in the form of triads of elements having similar chemical properties. Only three triads from the elements known at that time could be identified.
35. ans Now, let's see the merits of modern periodic table over Mendeleev's periodic table: i) Elements are arranged on the basis of their increasing atomic number. ii) Isotopes of an element can be placed with their parent element. iii) Lanthanides and actinides are placed separately.
36ans Na2O, ZnO, Al2O3 CO2, H2O. (a) Metal oxides that react with both acids and bases to produce salt and water are known as Amphoteric oxides. For example, zinc reacts with an acid or a base to produce salt and water. Amongst the given oxides, zinc oxide (ZnO) and aluminium oxide (Al2O3) are amphoteric oxides.
