Chapter 5 Periodic Classification of Elements Class 10 Science Extra Questions
Chapter 5 Periodic Classification of Elements Extra Questions and Answer
Chapter Name | Periodic Classification of Elements Extra Questions |
Class | CBSE Class 10 |
Textbook Name | Periodic Classification of Elements Class 10 |
Related Readings |
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Very Short Answer Type
Question 1. Name two elements whose properties were predicted on the basis of their positions in Mendeleev’s periodic table.
Answer
Gallium (Eka-aluminium) and germanium (Eka-silicon).
Question 2. Write the formulae of chlorides of Eka-silicon and Eka-aluminium, the elements predicted by Mendeleev. [NCERT Exemplar]
Answer
Eka-aluminium represents gallium (Ga) with valency three and Eka-silicon is for germanium (Ge) with valency four. The formulae of their respective chlorides are GaCl3 and GeCl4.
Question 3. How many elements are there in period 2?
Answer
Eight (8).
Question 4. Name all the elements present in group – 17 of the Modern Periodic Table.
Answer
F, Cl, Br, I, At.
Question 5. Name two elements whose atomic weight were corrected on the basis of their position in Mendeleev’s periodic table.
Answer
Gold (Au) and platinum (Pt).
Question 6. Arrange the following elements in the increasing order of their metallic character.
Mg, Ca, K, Ge, Ga [NCERT Exemplar]
Answer
Ge < Ga Mg < Ca < K.
Question 7. Name the scientist who proposed the Modern Periodic Law.
Answer
Henry Moseley, a scientist, proposed the Modern Periodic Law.
Question 8. What is meant by a group in the periodic table?
Answer
Groups are the vertical columns/vertical lines in the periodic table.
Question 9. What is meant by a period in the periodic table?
Answer
Periods are the horizontal rows in the periodic table.
Question 10. Name the elements present in period 1 of the modern periodic table.
Answer
Hydrogen (H) and Helium (He).
Question 11. An element A is in group II (group 2) of the periodic table:
(а) What will be the formula of its chloride?
(b) What will be the formula of its oxide?
Answer
(a) ACl2
(b) AO.
Question 12. Why are the elements calcium, strontium and barium named as alkaline earths?
Answer
These elements are called alkaline earths because their oxides are alkaline in nature and exist in the earth.
Question 13. Give the name and electronic configuration of second alkali metal.
Answer
The second alkali metal is sodium (Na). Its electronic configuration is 2, 8, 1.
Question 14. What are Metalloids?
Answer
Those elements which show some properties of both metals and non-metals are called metalloids. Examples: Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium and Polonium.
Question 15. Name three elements whose atomic masses were correct on the basis of their positions in Mendeleev’s periodic table.
Answer
- Beryllium (Be, group II A)
- gold (Au, group II B)
- platinum (Pt, group VIII).
Question 16. Name three elements which behave as metalloids.
Answer
The elements are:
- arsenic (As)
- antimony (Sb)
- germanium (Ge).
Question 17. Name the inert gas which has two electrons in its valence shell.
Answer
Helium.
Question 18. Name the most metallic and most non-metallic element in the Periodic Table.
Answer
The most metallic elements is francium (group 1) and most non-metallic element is fluorine (group 17).
Question 19. In the Modern Periodic Table, which are the metals among the first ten elements?
Answer
Lithium (Li), Beryllium (Be) and Boron (B) are the metal elements among first ten elements in the Modern Periodic Table.
Question 20. Two elements A and B belong to the same period. What is common in them?
Answer
They have the same number of shells.
Question 21. The electronic configuration of an element is 2, 8, 6. Identify the element and name of the family to which it belongs.
Answer
The element with configuration 2, 8, 6 (Z = 16) is sulphur. It belongs to the oxygen family.
Question 22. Calcium, Strontium and Barium form a Dobereiner’s triad. The atomic masses of calcium and Barium are 40 and 137 respectively. Predict the atomic mass of strontium.
Answer
According to Dobereiner’s triad, atomic mass of strontium is the arithmetic means of Ca and Ba as strontium lies between Ca and Ba.
Question 23. The formula of magnesium oxides is MgO. Write the formula of magnesium chloride.
Answer
Oxygen is divalent in nature. The valency of magnesium in magnesium oxide is +2. The formula of magnesium chloride is MgCl2 since chlorine has valency equal to one.
Question 24. State whether the following statement is true or false?
The valency of an element of group 17 is 7.
Answer
This statement is wrong. The number of valence electrons in an element of group 17 = 17 – 10 = 7.
Therefore, the valency of the element = 8 – 7 = 1.
Question 25. Name two elements whose atomic weight were corrected on the basis of their position in Mendeleev periodic table.
Answer
- Gold (Au)
- Platinum (Pt).
Question 26. The two isotopes of chlorine have atomic mass 35.4 and 37.4. Should they be placed in separate slots in the modern periodic table?
Answer
No, they should be placed in the same slot because the modern periodic table is based on the atomic number of the elements.
Question 27. List any two properties of the elements belonging to the first group of the modem periodic table. [Delhi 2014]
Answer
Elements of first group have one valence electron each in their atoms. All the elements of group 1 have the same valency of 1.
Question 28. What is the basic difference in the electronic configuration of the elements belonging to group 1 and group 2?
Answer
All elements belonging to group 1 have one electron in the valence shell while all elements belonging to group 2 have two electrons in their valence shell.
Question 29. Element ‘Y’ with atomic number 3 combines with element ‘A’ with atomic number 17. What will be the formula of the compound?
Answer
The electronic distribution in elements ‘A’ and ‘Y’ are 2, 1 and 2, 8, 7 respectively. Both have valency equal to 1. The formula of the compound is AY.
Question 30. Name the property which remains unchanged on descending a group in the periodic table.
Answer
Valence electrons.
Question 31. An element X is in group 13 of the periodic table. What is the formula of its oxide?
Answer
X2O3.
Question 32. Elements ‘X’ and TP belong to groups 1 and 17 of the periodic table respectively. What will be the nature of the bond in the compound XY?
Answer
Ionic bond.
Short Answer Type
Question 1. The three elements A, B and C with similar properties have atomic masses X, Y and Z respectively. The mass of Y is approximately equal to the average mass of X and Z. What is such an arrangement of elements called? Give one example of such a set of elements. [NCERT Exemplar]
Answer
The arrangement of these elements is known as Dobereiner triad. Example, Lithium, sodium and Potassium.
Question 2. In group I of the periodic table, three elements X, Y and Z have atomic radii 1.33 A, 0.95 A and 0.60 A respectively. Arrange the elements (X, Y and Z) in the increasing order of atomic number and mention a suitable reason for it.
Answer
In a given group, the atomic radii increases on moving down the group. Therefore, the arrangement of the given elements in the increasing order of their atomic numbers is as follows: Z, Y, X.
Question 3. Elements have been arranged in the following sequence on the basis of their increasing atomic masses.
F, Na, Mg, Al, Si, P, S, Cl, Ar, K
(a) Pick two sets of elements which have similar properties.
(b) The given sequence represents which law of classification of elements? [NCERT Exemplar]
Answer
(a) F and Cl are first and eighth element in the above sequence, therefore, they have similar properties.
Please note that although Na and K have similar properties but they are not related as first and eighth element in the above sequence.
(b) This sequence represents Newland’s Law of Octaves.
Question 4. State and explain Mendeleev’s periodic law.
Answer
According to Mendeleev’s periodic law “Physical and chemical properties of elements are periodic function of their atomic masses”.
If elements are arranged in the increasing order of atomic masses, elements with similar properties lies after a certain interval in the periodic table.
Question 5. “Hydrogen occupies a unique position in the Modern Periodic Table”. Justify the statement. [NCERT Exemplar]
Answer
The position of the element hydrogen is still not clear even in the Modern Periodic Table.
In electronic configuration, it resembles alkali metals of group 1. All of them have only one electron in the valence shell. Actually, hydrogen has only one shell (K-shell) which has one electron.
In characteristics, it resembles halogens of group 17. For example, like halogens hydrogen is a non-metal and diatomic as well. It has been therefore, decided to assign hydrogen a unique position in the Modern or Long Form Periodic Table. It is placed at the top in group 1 of alkali metals. However, it is not a member of that group.
Question 6. If an element X is placed in group 14, what will be the formula and the nature of bonding of its chloride? [NCERT Exemplar]
Answer
Since element “X’ is placed in group 14, therefore, its valency is 14 – 10 = 4. Further, since it is difficult to either lose all the four valence electrons or gain four more electrons, therefore, it prefers to share these four electrons to acquire the stable electronic configuration of the nearest inert gas. Its formula will be XCl4 . Thus, the nature of the chloride of element ‘X’ is covalent.
Question 7. Explain clearly, why atomic number of an element is most important to the chemist than its relative atomic mass.
Answer
Atomic number corresponds to the number of electron in an atom or it reflects the electronic configuration of the element. The elements having similar electronic configurations can then be placed together in the same group, it helps in the systematic classification of elements.
On the other hand, the atomic mass of an element does not provide the electronic configuration of an element, so atomic number is more fundamental property for classification of elements.
Question 8. What is the need of classification of the elements?
Answer
The following reasons can be assigned for practical utility of classification of elements:
- To make the study of chemical elements easier.
- To correct atomic masses of various elements.
- To discover new elements.
Question 9. The elements calcium, strontium and barium were put in one group or family on the basis of their similar properties.
(i) Mention the two similar properties?
(ii) What is the usual name of this group or family?
Answer
(i) (a) All these elements are metals.
(b) All these elements have a valency of 2.
(ii) The usual name of this group or family is alkaline earth metals.
Question 10. How does the electronic configuration of an atom of an element relate to its position in the modem periodic table? Explain with one example. [CBSE 2011 (Delhi)]
Answer
The electronic configuration of an atom of an element gives its position in the modern periodic table.
(i) The ‘period number’ of an element is equal to the number of electron shells in its atom.
(ii) The group number of an element having upto two valence electrons is equal to the number of valence electrons.
The group number of an element having more than 2 valence electrons is equal to the number of valence electrons plus 10.
Example: If the electronic configuration of an element is 2, 8, 7.
Then its period number is 3 as it has three electrons shells.
Its group number is 17 as it has 7 valence electrons. (∵ Group no. = 7 + 10 = 17)
Question 11. An element X (atomic number 17) combines with an element Y (atomic number 20) to form a compound.
(i) Write the positions of these elements in the modern periodic table.
(ii) Write the formula of the compound formed. Justify your answer in each case. [CBSE 2013]
Answer
(i) The electronic configurations of the two elements are:
X (Z = 17) 2, 8, 7 ; Y (Z = 20) 2, 8, 8, 2.
Element X is present in group 17 (halogen family) since it has 7 valence electrons. Element Y is placed in group 2 (alkaline earth family) since it has 2 valence electrons.
(ii) Element Y is a metal with valency 2 while element X is a non-metal with valency 1. Therefore, they two combine to form compound YX2 .
Question 12. Explain why:
(i) All the elements in a group have similar chemical properties.
(ii) All the elements in a period have different chemical properties.
Answer
(i) All the elements in a particular group have similar outer shell electronic configuration. Since chemical properties of an element are determined mainly by the outer shell configuration, all the elements in a group have similar chemical properties.
(ii) All the elements in a period have different valence shell electronic configuration because they have different number of electrons in the valence shell. Hence, the elements in a period have different chemical properties.
Question 13. Given below are the atomic radii of three elements X, Y and Z of the periodic table, each having n electrons in the outermost shell of their atoms:
|
Element |
X |
Y |
Z |
|
Atomic radii |
133 pm |
157 pm |
202 pm |
Answer the following:
(a) Do these elements X, Y and Z belong to same group or to the same period?
(b) Which element will be least metallic?
Answer
(a) Since the elements X, Y and Z contain same number of electrons (n) in the valence shell (outermost shell), they belong to the same group.
(b) In a group, the atomic radius increases on descending the group. Therefore, the element X with the smallest atomic radius is at the top of the group and the element Z having largest atomic radius is at the bottom.
Now, we know metallic character increases as we move from top to bottom in a group. Therefore, the least metallic element is X.
Question 14. (a) The elements of the second period along with their atomic numbers in parentheses are given below:
B (5), Be (4), O (8), N (7), Li (3), C (6), F (9)
(i) Arrange them in the same order as they appear in the periodic table.
(ii) Which element has the largest and smallest atom?
(b) Why does atomic radius change as we move from left to right in a period? [CBSE 2011]
Answer
(a) (i) Li (3), Be (4), B (5), C (6), N (7), O (8), F (9)
(ii) The element Li has the largest atom. The element F has the smallest atom.
(b) Along a period, the nuclear charge increases and the electrons are attracted more towards the nucleus. Therefore, the atomic size or atomic radius decreases as we move from left to the right along a period.
Question 15. Write two reasons responsible for the late discovery of noble gases. [CBSE 2013]
Answer
- Noble gas elements were not present in earth crust as minerals like other elements and were present in air to a very small extent.
- Their atoms have stable electronic configuration of their outermost shells also called valence shells. (2 in case of He and 8 for other elements). They do not combine with atoms of other elements.
That is why, noble gas elements were discovered at a later stage.
Question 16. From the following elements:
4Be, 9F, 19K, 20Ca
(i) Select the element having one electron in the outermost shell.
(ii) two elements of the same group.
Write the formula of and mention the nature of the compound formed by the union of 19K and element X (2, 8, 7). [Delhi 2015]
Answer
(i) 19K
(ii) 4Be, 20Ca belong to the same group.
Electronic configuration of K (19) = 2, 8, 8, 1 Valency of K = 1
Electronic configuration of X (2, 8, 7) Valency of X = 1
The formula of the compound formed is KX. The compound KX is of ionic nature.
The bond is formed by transference of electrons.