1. (c) The atoms lose their electrons more easily.
2. (b) Mg
3. (a) Neon
4. (a) All the elements in the in the same column as boron have three electrons in the valence shell. That is all the elements are trivalent.
(b) All the elements in the same column as fluorine has one electron in the valance shell, which is all the elements, are monovalent.
5. Chlorine has the electronic configuration 2, 8, 7.
(a) Atomic number of element is 17.
(b) F (9)
6. (a) A is a non-metal.
(b) C is less reactive than A.
(c) C will be smaller than B.
(d) A will form anion.
7. Nitrogen atomic number 7 has got 7 electrons with electronic configuration 2, 5. Phosphorus with atomic number 15 has got 15 electrons with electronic configuration 2, 8, 5.
Non-metallic character decreases as we move down the group. Therefore, nitrogen will be more electronegative than phosphorus.
8. Group number on an element can be predicted from the number of electrons in the outermost shell.
Period number of an element can be predicted from the number of shells with filled electrons.
Knowing the electronic configuration, we can find the number of electrons in the outermost shell and the number of shells with filled electrons. This can help to relate its position in the Periodic Table.
9. Elements in a group have similar properties. Elements with atomic numbers 12 and 38 lie in the same group as calcium. Therefore, they will have properties resembling calcium.
(a) In both tables, physical and chemical properties has been taken basis for classification and kept in same group.
(b) The formulae of the oxide and hydrides formed by an element were treated as one of the criteria for classification of elements.
(a) While Mendeleev’s Table was based on the atomic mass but modern Periodic table is based on atomic number.
(b) Mendeleev’s Table contain 6 periods and 8 groups but modern periodic table contain 7 periods and 18 groups.
(c) Transition elements have been placed at the end of Mendeleev’s periodic table but in modern periodic table they are placed in the middle.
11. Yes, following triads can be identified:
Li, Na, K
Be, Mg, Ca
The atomic mass of middle atom in the above triads is approximately equal to the average mass of elements on the left and right hand side.
12. Dobereneiner could identify only three triads from the elements known at that time. Hence, this classification of elements was not found to be useful.
13. The limitations of Newlands’ Law of Octaves:
(a) it was found that Law of Octaves was applicable only upto calcium. After calcium eighth element did not possess properties similar to that of first.
(b) Newlands’ assumed that only 56 elements existed in nature and no more elements would be discovered in future.
(c) To fit the element into his table, Newlands adjusted two elements in the same slot but also put some unlike elements under the same note.
14. K2O, CO2, SiO2, BaO
15. Scandium and Germanium.
16. Mendeleev created his Periodic Table on the basis of their fundamental property the atomic mass and also on the similarities of chemical properties. Among chemical properties he concentrated on the compounds formed by elements with oxygen and hydrogen.
17. Modern Periodic Table settled the placement of isotopes as isotopes have same atomic number.
Position of controversial position of hydrogen is also settled in modern periodic table.
18. Calcium and Strontium would show chemical reactions similar to magnesium. They have the same number of electrons in the outermost shell.
19. (a) Lithium, sodium and potassium have a single electron in their outermost shells.
(b) Magnesium and calcium have two electrons in their outermost shells.
(c) Helium, neon and argon have filled outermost shells.
20. (a) Lithium, sodium and potassium have same number of electrons in the outermost shell.
(b) Helium and argon have completed outermost shell, 2 electrons in case of helium and 8 electrons in case of argon.
21. Lithium and Beryllium are the metals among the first ten elements in the Modern Periodic Table.
22. Metallic character of an element increases down a group and decreases from left to right in period. On this basis Be is expected to have maximum metallic charecter