CBSE Class 10 Science Chapter-5 Periodic Classification of Elements Important Questions – 2 Mark Question
Important Questions for CBSE Class 10 Science Chapter 5 – Periodic Classification of Elements- 2 Mark Questions
1. Alkali metals do not form dipositive ions why?
Ans. The elements in Group 1 of the Modern Periodic Table, known as alkali metals, have only one valence electron. They tend to lose this electron to acquire the electron configuration of a noble gas, resulting in the formation of a positive ion.
2. The atomic numbers of three elements A, B and C are 12, 18 and 20 respectively. State giving reason, which two elements will show similar properties. (AI 2014)
Ans. The atomic number of element A is 12, which corresponds to an electronic configuration of 2, 8, 2. Similarly, element B with atomic number 18 has an electronic configuration of 2, 8, 8, and element C with atomic number 20 has an electronic configuration of 2, 8, 8, 2. As both A and C have two valence electrons in their outermost shell, they belong to group 2 and will show similar properties.
3. Why non-metals are called electro negative elements?
Ans. Non-metals are referred to as electronegative elements as their atoms tend to gain electrons to form negative ions.
4. State the Modern periodic law of classification of elements.
Ans.
The Modern Periodic Law states that the chemical and physical properties of elements are directly related to their atomic numbers and exhibit periodic trends.
5. How were the positions of different isotopes decided in the modern periodic table?
Ans. The Modern Periodic Table arranges elements based on their atomic numbers. As all isotopes of an element have the same atomic number, they are placed in the same position on the table. Therefore, isotopes of an element have the same placement in the Modern Periodic Table.
6.Write the atomic numbers of two elements ‘X’ and ‘Y’ having electronic configurations 2, 8, 2 and 2, 8, 6 respectively.
Ans.
The electronic configuration of element X is 2, 8, 2, which corresponds to an atomic number of 12 (2 + 8 + 2). Similarly, the electronic configuration of element Y is 2, 8, 6, which corresponds to an atomic number of 16 (2 + 8 + 6).
6. Hydrogen is regarded as a rogue element in the periodic table. Discuss.
Ans. Hydrogen is considered to be an anomalous element in the periodic table due to its unique properties and placement. While it is placed above the alkali metals based on its electronic configuration, it is actually a non-metal and shares similarities with the halogens in Group 17. Its placement in the periodic table is still a subject of debate.
7. List any two properties of the elements belonging to the first group of the Modern Periodic Tablet.
Ans.
Two properties of elements belonging to the first group:
(i) Elements in Group 1 have one valence electron in their outermost energy level, resulting in a valency of one.
(ii) Elements in Group 1, also known as Alkali metals, are electropositive in nature.
8. Why do elements in a group show same valency?
Ans. The valency of an element is determined by the valence shell electronic configuration of its atom. As elements within a group have the same valence shell electronic configuration, they exhibit the same valency.
9. Write any one difference in the electronic configurations of group 1 and group 2 elements.
Ans.
Elements in Group 1 have a single valence electron in their outermost energy level, while elements in Group 2 have two valence electrons in their outermost energy level.
10. Why are the members of group 1 known as alkali metals?
Ans. The elements in Group 1 are referred to as alkali metals due to their ability to react with water and form hydroxides that are soluble and known as alkalis.
11. Write the number of horizontal rows in the Modern Periodic Table. What are these rows called?
Ans.
The Modern Periodic Table has seven horizontal rows of elements, referred to as periods.
12. How does metallic character of the elements vary (i) In a group (ii) In a period?
Ans. (i) The metallic properties of elements increase as you move down a group.
(ii) The metallic properties of elements decrease as you move from left to right across a period.
13. Define electropositivity.
Ans. The measure of the ability of elements, primarily metals, to give away electrons and form positive ions is known as electropositivity.
14. Did Dobereiner’s triads also exist in the columns of Newland’s Octaves? Compare and find out?
Ans. It is possible to identify the following triads: Li, Na, K and Be, Mg, Ca. In these triads, the atomic mass of the middle element is approximately the average of the masses of the elements on either side.
15. Why did Mendeleev leave some gaps in the Periodic table?
Ans. Mendeleev’s periodic table had some empty spaces for elements that had yet to be discovered. He was able to predict the properties of these elements based on their position in the table. For instance, he predicted the properties of gallium (also known as eka-aluminum) and germanium (also known as eka-silicon) which were not yet known at the time.
16. What were the limitations of Dobereiner’s classification?
Ans. Debereneiner’s classification of elements based on the triads was not found to be practical as it could only identify three triads from the known elements at the time.
17. State Mendeleev s Periodic law.
Ans. Medeleev’s periodic law states that the properties of elements are periodic in relation to their atomic masses.
18. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)
Ans. Two elements that were later discovered and found to fit into the gaps left by Mendeleev in his Periodic Table are scandium and germanium.
19. How could the Modern Periodic table remove various anomalies of Mendeleev’s Periodic Table?
Ans. The modern Periodic Table resolves the placement of isotopes, as all isotopes of an element have the same atomic number and are therefore assigned the same position in the table. Additionally, the modern table also addresses the previously uncertain position of hydrogen.
20. Out of the three elements P, Q and R having atomic numbers 11, 17 and 19 respectively, which two elements will show similar properties and why?
Ans. The elements P, Q, and R have distinct atomic numbers of 11, 17, and 19 respectively. By analyzing their electronic configurations, it can be deduced that P and R belong to group 1 as they have one valence electron and a valency of 1. This suggests that P and R will have similar properties. However, Q, with an electronic configuration of 2, 8, 7, belongs to a different group and may have different properties.
Additional and long Important Questions for CBSE Class 10 Science Chapter 5 – Periodic Classification of Elements
21. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?
Ans. Elements belonging to the same group, such as Calcium and Strontium, have similar chemical properties due to their shared number of electrons in their outermost shell.
22. In the Modern Periodic Table, which are the metals among the first ten elements?
Ans. In the Modern Periodic Table, the metals among the first ten elements are: Hydrogen, Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Fluorine, Neon.
23. What property do all elements in the same column of the Periodic Table as boron have in common?
Ans. All elements in the same column (group) as boron have the same number of electrons in their outermost energy level (valence shell). This is the reason why elements in the same group have similar chemical and physical properties.
24. What property do all elements in the same column of the Periodic Table as Fluorine have common?
Ans. All elements in the same column (group or family) of the Periodic Table as Fluorine have the same number of valence electrons. They all belong to group 17, also known as the halogens, and have seven valence electrons in their outermost energy level. This gives them similar chemical properties, such as high reactivity and the ability to form compounds by gaining one electron to fill their outermost energy level.
25. Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the Periodic Table. Write the electronic configuration of these two elements. Which of these will be more electronegative? Why?
Ans. The electronic configuration of Nitrogen is 2,5 and electronic configuration of Phosphorus is 2,8,5.
Phosphorus (atomic number 15) will be more electronegative than Nitrogen (atomic number 7) because as you move across a period (row) in the periodic table, the atomic number increases and the number of protons in the nucleus increases. As a result, the valence electrons are pulled closer to the nucleus and are held more tightly, making the element more electronegative.
26. In the modern Periodic Table calcium (atomic number 20) is surrounded by elements with atomic number 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium?
Ans. Calcium (atomic number 20) is in the 4th period and belongs to group 2 of the Periodic Table. The elements with atomic numbers 12, 19, 21, and 38 that surround it are Magnesium (atomic number 12), Potassium (atomic number 19), Scandium (atomic number 21), and Strontium (atomic number 38). Among these, Strontium (atomic number 38) would have physical and chemical properties resembling Calcium as both have the same number of electrons in the outermost shell and belong to the same group.
27. Write the formula used to determine the maximum number of electrons which a shell in an atom can accommodate.
Ans. The formula used to determine the maximum number of electrons which a shell in an atom can accommodate is 2n^2, where n is the principle quantum number of the shell.
28. How it can be proved that the basic structure of the Modern Periodic Table is based on the electronic configuration of atoms of different elements?
Ans. It can be proved that the basic structure of the Modern Periodic Table is based on the electronic configuration of atoms of different elements by comparing the electron configurations of elements in the same group or period of the periodic table. Elements in the same group or period have similar electron configurations and therefore exhibit similar chemical properties. Additionally, the electron configurations of elements can be used to predict their positions in the periodic table. For example, elements with similar valence electron configurations will be placed in the same group of the periodic table. This is consistent with the Modern Periodic Table, which organizes elements based on their electron configurations.
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