NCERT Solutions for Class 10 Science Chapter 5 Periodic Classification of Elements
Periodic classification of elements: Needs for classification, Modern Periodic table, gradation in properties, valency, atomic number, metallic and non-metallic properties.
|Chapter Name||Periodic Classification of Elements|
|Number of Questions Solved||23|
Did Dobereiner’s triads also exist in the columns of Newlands Octaves? Compare and find out.
Yes, Dobereiner’s triads also exist in the columns of Newlands Octaves. For example, the second column of Newlands classification has the elements lithium (Li), sodium (Na) and Potassium (K), which constitute a Dobereiner’s triad.
What were the limitations of Dobereiner’s classification?
All the known elements could not be arranged in the form of triads. For very low mass or for very high mass elements, the Dobereiner’s triads are not applicable. Take the example of F, Cl and Br. Atomic mass of Cl is not an arithmetic mean of atomic masses of F and Br. As the techniques for measuring atomic masses accurately, improved, the Dobereiner’s triad was unable to remain strictly valid.
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What were the limitations of Newland’s Law of Octaves?
It was not valid for elements that had atomic masses higher than Ca.When more elements were discovered, such as elements from the noble gases such as He, Ne, Ar, they could not be accommodated in his table.
Use Mendeleev’s periodic table to predict the formulae for the oxides of the following elements: K, C, Al, Si, Ba.
K2O – Potassium Oxide
CaO – Calcium Oxide
Al2O3 – Aluminium Oxide
SiO2 – Silicon dioxide
BaO – Barium Oxide.
Besides gallium, which other elements have been left by Mendeleev in his periodic table, since the time they were discovered? (Any two)
Scandium and Germanium.
What were the criteria used by Mendeleev in creating his periodic table?
He observed the relationship between the atomic masses of the elements and their physical properties. Among chemical properties, he concentrated on the compounds formed by elements with oxygen and hydrogen.
Why do you think, the noble gases are placed in a separate group?
Due to its inert and low concentration in our atmosphere, they could be placed in a new group without disturbing the existing order.
How could the Modern periodic table remove various anomalies of Mendeleev’s periodic table?
When the elements are arranged according to their atomic numbers on the basis of modern periodic law, all the anomalies (defects) of Mendeleev’s classification disappear. For example, Position of isotopes: All the isotopes of an element have the same number of protons, so their atomic number is also the same. Since all the isotopes of an element have the same atomic number, they can be put at one place in the same group of the periodic table.
Name two elements, which you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?
Calcium and Beryllium are the elements that will show chemical reactions similar to magnesium. This is because beryllium and calcium belong to the same group of periodic table as magnesium. All of them have similar electronic configurations with 2 valence electrons each.
a. Three elements that have a single electron in their outermost shell.<
b. Two elements that have two electrons in their outermost shell.<
c. Three elements with filled outermost shell.
a. Three elements that have a single electron in their outermost shell are:
b. Two elements that have two electrons in their outermost shell are:
c. Three elements with filled outermost shell are:
a. Lithium, sodium, potassium are metals that react with water to liberate hydrogen. Is there any similarity in the atoms of these elements?
b. Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common
a. These elements are alkali metals and they have 1 valence electron in their outermost shell and are therefore very unstable and reactive.
b. These elements each have full outermost subshell, which results in high stability. They only react with other elements in extreme circumstances, the trait for which they are named.
In the Modern periodic table, which are the metals among the first ten elements?
The metals are Lithium and Beryllium.
By considering their position in the periodic table, which one of the following elements would you expect to have maximum metallic characteristic?
Ga, Ge, As, Se, Be
Which of the following statements is not a correct statement about the trends when going from left to right across the periods of the periodic table?<
(i)The elements become less metallic in nature
(ii) The number of valence electrons increases
(iii) The atoms lose their electrons more easily
(iv) The oxides become more acidic
(iii) The atoms lose their electrons more easily – Incorrect statement.
Element X forms a chloride with the formula XCl2, which is a solid with a high melting point. X would most likely be in the same group of the periodic table as
a. Na b. Mg c. Al d. Si
Which element has?
a.Two shells, both of which are completely filled with electrons?<
b. The electronic configuration of 2,8,2?<
c. A total of three shells, with four electrons in its valence shell?<
d. A total of two shells, with three electrons in its valence shell?<
e. Twice as many electrons in its second shell, as in its first shell?
a. Neon (2,8)
b. Magnesium (2,8,2)
c. Silicon (2,8,4)
d. Boron (2,3)
e. Carbon (2,4)
What property do all elements in the same column of the periodic table as fluorine have in common?
These elements all have 7 electrons in their outermost shells and these often exist as salts, combined with elements from the Alkali metal group.
An atom has electronic configuration 2,8,7.
i. What is the atomic number of this element?
ii. To which of the following elements would it be chemically similar<
N (7) F (9) P (15) Ar (18)
(i) Chlorine – 17
(ii) F (9)
Which type of ion, cation or anion, will be formed by element A?
C is less reactive than A
“C” will be smaller in size than “B” as the atomic size decreases as we go across a period.
Anion will be formed by element A
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?
Electronic configuration – Nitrogen – 2s2 2p3 and Phosphorus – 1s2 2s2 2p6 3s2 3p3. Nitrogen will be more electronegative; this is because its atom has small size due to which the attraction of its nucleus for the incoming electron is more.
How does the electronic configuration of an atom relate to its position in the Modern periodic table?
The electronic configuration of an atom increases in the outermost valence shell which relates to its position in the Modern periodic table.
In the Modern periodic table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium?
The atomic number of calcium is 20, so its electronic configuration is 2, 8, 8, 2. Thus, calcium has 2 valence electrons (in its outermost shell). Now, the element which has 2 valence electrons, will have physical and chemical properties resembling to that of calcium. The electronic configuration of element having atomic number 12 is 2, 8, 2. It has 2 valence electrons just like calcium. So, the element having atomic number 12 will have physical and chemical properties resembling that of calcium.
Where do you think should hydrogen be placed in the Modern periodic table?
Hydrogen element has been placed at the top of group 1, above the alkali metals because the electronic configuration of hydrogen is similar to those of alkali metals.
Multiple Choice Questions (MCQs) [1 Mark each]
Which of the following is the outermost shell for elements of 2nd period? [NCERT Exemplar]
(b) The elements of 2nd period involve the filling of 2nd shell, i.e. Z-shell. Because in period 2, there are two shell, K and L
An element which is an essential constituent of all organic compounds belongs to [NCERT Exemplar]
(a) group 1
(b) group 14
(c) group 15
(d) group 16
(b) Constituent of all organic compounds is carbon. It belongs to group 14.
Which one of the following elements exhibit maximum number of valence electrons? [NCERT Exemplar]
(d) Na (group 1) has one, A1 (group 13) has three (13 -10), Si (group 14) has four (14-10) and P (group 15) has five (15 – 10) valence electrons. Therefore, P has maximum number of valence electrons, i.e.3 (maximum among the given elements).
Which of the given elements A, B, C, D and E with atomic number 2, 3, 7, 10 and 30 respectively belong to the same period? [NCERT Exemplar]
(a) A, B, C
(b) B, C, D
(c) A, D, E
(d) B, D, E
(b) 2nd period contains elements with atomic number 3(Li), 7(N), 10(Ne). Since, 2nd period has elements having atomic number 3 to 10.
The elements A, B, C, D and E have atomic number 9, 11, 17, 12 and 13 respectively. Which pair of elements belong to the same group? [NCERT Exemplar]
(a) A and B
(b) B and D
(c) A and C
(d) D and E
(c) Electronic configuration of A (atomic number = 9) is 2, 7.
Electronic configuration of B (atomic number = 11) is 2, 8,1.
Electronic configuration of C (atomic number = 17) is 2, 8, 7.
Electronic configuration of D (atomic number =12) is 2, 8, 2.
Electronic configuration of E (atomic number =13) is 2, 8, 3.
Elements which differ in atomic number by 8, i.e. 9 (A, fluorine) and 17 (C, chlorine) lie in the same group, i.e. group 17 (halogen).
In Mendeleev’s periodic table, gaps were left for the elements to be discovered later. Which one of the following elements found a place in the periodic table later? [NCERT Exemplar]
(a) Mendeleev’s left some gaps in the periodic table for those elements which were not known at that time. Germanium element found a place in the periodic table later and Mendeleev’s predictions were found to be remarkably correct
Which of the following are the characteristics of isotopes of an element? [NCERT Exemplar]
(i) Isotopes of an element have same atomic masses.
(ii) Isotopes of an element have same atomic number.
(iii) Isotopes of an element show same physical properties.
(iv) Isotopes of an element show same chemical properties.
(a) (i), (iii) and (iv)
(b) (ii), (iii) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)
(d) Isotopes of an element have same atomic number and show same chemical properties.
Which of the following elements would lose an electron easily? [NCERT Exemplar]
(c) Electronic configuration of Mg (atomic number = 12) 2, 8, 2
Electronic configuration of Na (atomic number = 11)2, 8, 1
Electronic configuration of K (atomic number=19) 2, 8, 8, 1
Electronic configuration of Ca (atomic number =20) 2, 8, 8, 2
From the above electronic configurations, it is clear that K and Na will lose electron easily to achieve stable configuration. But out of K and Na, K will lose electron more easily because the force of, attraction on valence electron of K is least among the given elements.
Which among the following elements has the largest atomic radii? [NCERT Exemplar]
(c) Atomic radius increases on moving down in a group. Na and K are in the same group and K is below Na, so K will have higher atomic radius, i.e. K > Na. In a period on moving left to right, atomic radius decreases. Since, K and Ca are in the same period and K is in 1st group and Ca is in 2nd group, so atomic radius of K will be more than Ca, i.e. K > Ca.
Also Na and Mg are in the same period, but Na belongs to 1st group and Mg belongs to 2nd group, so atomic radius of Na is more than Mg, i.e. Na > Mg. Thus, if we take all these together we get K > Na >Mg and K > Ca > Mg. Hence, we can say that the atomic radius of K is largest.
Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic table? [NCERT]
(a) The elements become less metallic in nature
(b) The number of valence electrons increases
(c) The atoms lose their electrons more easily
(d) The oxides become more acidic
(c) On moving from left to right, the atomic number increases and hence, the nude charge increases. With the increase of nudear charge, the force binding the electron increases so the atom lose the electrons with more difficulty, not easily.
Which one of the following depicts the correct representation of atomic radius (r) of an atom? [NCERT Exemplar]
(a) (i) and (i)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
(b) Atomic radius is the distance between nucleus and outermpst shell [consisting electron(s)]. Hence (ii) and (iii) are the correct representations.
Which of the following statement(s) about the modern periodic table are incorrect?
(i) The elements in the modern periodic table are arranged on the basis of their decreasing atomic numbers.
(ii) The elements in the modern periodic table are arranged on the basis of their increasing atomic masses.
(iii) Isotopes are placed in adjoining group(s) in the periodic table.
(iv) The elements in the modern periodic table are arranged on the basis of their increasing atomic number. [NCERT Exemplar]
(a) Only (i)
(b) (i), (ii) and (iii)
(c) (i), (ii) and (iv)
(d) Only (iv)
(b) Only statement (iv) is correct. All the elements in the modern periodic table are arranged on the basis of their increasing atomic number. All the isotopes can be placed at one place in the same group of the periodic table.
The element with atomic number 14 is hard and forms acidic oxide and a covalent halide. To which of the following categories does the element belong? [NCERT Exemplar]
(d) Left-hand side element
(c) Its outermost shell has 4 electrons. So, it is a non-metal. Non-metal forms acidic oxide and by sharing of electrons with halogen, it forms covalent halide.
Arrange the following elements in the order of their decreasing metallic character Na, Si, Cl, Mg, Al. [NCERT Exemplar]
(a) Cl > Si > Al > Mg > Na
(b) Na > Mg > Al > Si > Cl
(c) Na > Al > Mg > Cl > Si
(d) Al > Na > Si > Ca > Mg
(b) Metals lie on the extreme left side of the periodic table. Metallic character decreases from left to right in a period. Na, Si, Cl, Mg, Al belong to same period in the order Na, Mg, Al, Si, Cl. On moving in a i period from left to right, the metallic character decreases. Thus, the order of decreasing metallic character is: Na > Mg > Al > Si > Cl
Which of the following set of elements is written in order of their increasing metallic character? [NCERT Exemplar]
(a) Be, Mg, Ca
(b) Na, Li, K
(c) Mg, Al, Si
(d) C, O, N
(a) Metallic character increases as we go down in a group.
Which one of the following does not increase while moving down the group of the periodic table? [NCERT Exemplar]
(a) Atomic radius
(b) Metallic character
(c) Valence electrons
(d) Number of shells in an element
(c) Elements in each group has some number of valence electrons hence have same valency and thus exhibit similar chemical properties.
The elements X, Y and Z are shown in a portion of periodic table. What would be the representations of ionic forms of X and Z respectively?
(a) X– and Z+
(b) X+ and Z–
(c) X2- and Z2+
(d) X2+and Z2-
(a) X having 1 electron less than that of Y, which is a noble gas (having complete octet), will tend to gain 1 electron while Z will tend to lose 1 electron to achieve complete octet configuration. Hence, they will have ionic formula as X– and Z+.
which of the following elements will form an acidic oxide? [NCERT Exemplar]
(a) An element with atomic number = 7
(b) An element with atomic number = 3
(c) An element with atomic number = 12
(d) An element with atomic number = 19
(a) Non-metals form acidic oxides in general. Non-metals have 4 to 8 electrons in the outermost shell. The electronic configuration of given elements are (a) i.e. 7 = 2, 5 (b) i.e. 3 =2, 1 (c) i.e. 12 =2, 8, 2 (d)i.e. 19=2, 8, 8,1.
So, element with atomic number = 7 (electronic configuration = 2, 5) with is non-metal (N) and it will form an acidic oxide. Rest three elements with atomic- numbers, 3 (Li), 12 (Mg) and 19 (K) are metals and hence, form basic oxides.
what type of oxide would Eka-aluminium form? [NCERT Exemplar]
(c) Gallium has a valency of 3. Hence, it forms an oxide having molecular formula E2O3. In other options, valency of E is not 3.
The diagram given below shows the position of elements in a portion of the periodic table. Ionic compound is formed between ………. and ………
(a) A and B
(b) B and E
(c) C and D
(d) D and E
(D) being in group IIA is most electropositive among given elements while E being in group VIIA is most electronegative among the given elements. Hence, both of these will form ionic compound, more readily than the other given elements.
Element X forms a chloride with formula, XCl2, which is a solid with a high melting point. X would most likely to be in the same group of the periodic table as [NCERT]
(b) The formula of chloride is XCl2, that means the valency of the element X is 2. The element having valency 2 will be present in group 2. Out of the given choices magnesium (Mg) belongs to group 2.
The adjacent diagram represents the arrangement of the atoms of an element (having valency = 4) forming giant covalent network.
Identify the heavy metal which belongs to same group as the element discussed above.
(c) The element discussed in diagram is carbon. Carbon (C) and lead (Pb) both belong to group IVA.
Arrange the elements, represented by alphabets p, q, r, s and t in the above shown outline of periodic table, in increasing order of their valency.
(a) t < q < r < s < p
(b) s < t < q < r < p
(c) s < q < t < r < p
(d) q < s < t < p < r
(c) p(group IVA), q(group VIIA), r(group IILA) s(group VIII) and t(group IIA) has valency 4, 1, 3, 0 and 2 respectively hence the correct order of increasing valency is: s(0) < q(1) < t(2) < r(3) < p(4)
The diagram given above represents outline of the periodic table. The alphabets p, q, r, s and t represent elements. Which one of the following pairs of alphabets represents elements which consists of same number of shells in their atom?
(a) p and q
(b) r and t
(c) p and s
(d) g and s
(d) Elements q and s belong to same period of the periodic table and hence, will have same number of shell.
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