1. Alkali metals do not form dipositive ions. why?
Ans. Alkali metals are present in Group 1 so 17 has only one valence electron. By losing one e– They acquire the configuration of the noble gas element and hence do not form dispositive ions.
2. Why are non-metals called electronegative elements?
Ans. Non-metals are called electronegative elements since their atoms form negative ions by accepting electrons.
3. How were the positions of different isotopes decided in the modern periodic table?
Ans. All the isotopes have the same atomic numbers in the modern periodic table the elements have been allotted places based on their atomic numbers. Therefore, all the isotopes of an element have been assigned the same position in the modern periodic table.
4. Hydrogen is regarded as a ‘rogue’ element in the periodic table. Discuss.
Ans. Hydrogen is regarded as a rogue element in the periodic table because till today its position is not satisfactory. Although it has been placed on the top of alkali metals on the basis of electronic configuration, but it is non-metal and also resembles halogens of group 17.
5. Why do elements in a group show same valency.
Ans. The valency of an element is related to the valence shall electronic configuration of its atom. Since the elements present in a group have the same valence shell electronic configuration. They show the same valency.
6. Why are the members of group 1 known as alkali metals.
Ans. All the elements in group 1 are known as alkali metals because they react with water to form soluble hydroxides that are called alkalis.
7. How does metallic character of the elements vary (i) In a group (ii) In a period.
Ans. (i) The metallic character of the elements increases downwards in a group
(ii) The metallic character of the elements decreases from left to right is a period.
8. Name other elements which belong to the same family as
(i) Calcium (ii) Carbon.
Ans.(i) Magnesium. (ii) Strontium.
9. Did Dobereiner’s triads also exist in the columns of Newland’s Octaves. Compare and find out.
Ans. Yes, the following triads can be identified:
Li, Na, K
Be, Mg, Ca
The atomic mass of the middle atom in the above triads is approximately equal to the average mass of elements on the left and right-hand side.
10. What were the limitations of Dobereiner’s classification?
Ans. Dobereiner’s could identify only three triads from the elements known at that time. Hence, this classification of elements was not found to be useful.
11. How could the Modern Periodic table remove various anomalies of Mendeleev’s Periodic Table.
Ans. Modern Periodic Table settled the placement of isotopes as isotopes have the same atomic number. The position of hydrogen was also settled in the modern periodic table.
12. Name two elements you would expect to show chemical reactions similar to Magnesium. What is the basis for your choice?
Ans. Calcium and Strontium would show chemical reactions similar to Magnesium. They have the same number of electrons in the outermost shell.