NCERT Solution Science Class 10 Chapter 5 Periodic Classification of Elements
NCERT Solution Science Class 10 Chapter 5 Periodic Classification of Elements all questions and answers. Science Class 10 5th Chapter Periodic Classification of Elements exercise solution and experts answer. As one of online learning platforms, we (netex.) are excited to offer the NCERT Solution Science Class 10 Chapter 5. This solution is designed to help students who are looking to brush up on their Science concepts on Chapter 5 Periodic Classification of Elements.
Page no: 81
1.) Did Döbereiner’s triads also exist in the columns of Newlands’ Octaves? Compare and find out.
Ans 1- Yes, Dobereiner triads exist in Newland law of octaves.
E.g.- Li, Na, K
This was in the triads but also found in law of octaves but with different explanation that was lithium as the first element so the sodium as eighth element. If we consider sodium as first element then potassium is the eighth element.
2.) What were the limitations of Döbereiner’s classification?
Ans 2- Dobereiner could identify only three triads from the elements known at that time.
3.) What were the limitations of Newlands’ Law of Octaves?
Ans 3- Limitation of Newland law of octaves-
i) It was applicable only up to calcium.
ii) He had assumed that only 56th element exist in nature and no more elements would be discovered.
iii) He had adjusted two elements in same slot but also put unlike elements in the same note.
E.g.- Cobalt and nickel in same slot, but these are placed in same column with the fluorine, chlorine and bromine.
Page no: 85
1.) Use Mendeléev’s Periodic Table to predict the formulae for the oxides of the following elements:
K, C, AI, Si, Ba.
Ans 1- K2O, CO2, Al2O3, SiO2 and BaO.
2.) Besides gallium, which other elements have since been discovered that were left by Mendeléev in his Periodic Table? (any two)
Ans 2- Scandium and Germanium as similar properties to Eka- boron and Eka- silicon respectively.
3.) What were the criteria used by Mendeléev in creating his Periodic Table?
Ans 3- The criteria used by Mendeleev was the atomic mass and similar chemical properties.
4.) Why do you think the noble gases are placed in a separate group?
Ans 4- Noble gas are less reactive or we can say chemically inert. Their concentration in atmosphere is also very low.
Page no: 90
1.) How could the Modern Periodic Table remove various anomalies of Mendeléev’s Periodic Table?
Ans 1- The modern periodic table remove the anomalies of Mendeleev periodic table: –
i) In modern periodic table position of hydrogen is fixed i.e placed at the top of the alkali metals.
ii) Modern periodic table is based on atomic number and Mendeleev periodic table is based on atomic mass.
iii) Cobalt and nickel are placed at 9th and 10th position.
iv) Isotopes of same elements are placed in same position of that element.
2.) Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?
Ans 2- Beryllium and Calcium would show similar chemical properties to Magnesium because of similar electronic configuration.
Be: 2, 2
Ca: 2, 8, 8, 2
Mg: 2, 8, 2
i.e same no. of valence electrons. Hence, same no. of valency i.e similar chemical behaviour.
3.) Name
(a) three elements that have a single electron in their outermost shells.
(b) two elements that have two electrons in their outermost shells.
(c) three elements with filled outermost shells.
Ans 3- i) Lithium (Atomic no- 3) – E.C- 2,1
Sodium (Atomic no- 11) – E.C- 2, 8, 1
Potassium ( Atomic no- 19) – E.C- 2, 8, 8,1
ii) Beryllium(2, 2) and Magnesium(2, 8, 2).
iii) Helium(2), Neon(2, 8) and Argon(2, 8, 8)
4.) (a) Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. 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?
Ans 4- i) Lithium, Sodium and potassium all belong to same group i.e alkali metals group. All have one valence electrons in their outermost shell and same valency of +1.
ii) Both helium and neon have completely filled outermost shell i.e they are inert.
He- 2
Ne- 2, 8
5.) In the Modern Periodic Table, which are the metals among the first ten elements?
Ans 5- The first ten element are hydrogen, helium, lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine, neon.
Out of these Lithium, Beryllium and Boron are metals.
6.) 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
Ans 6- Beryllium have maximum metallic characteristics as it is placed on the left side of periodic table. As moving from left to right the metallic character decreases. Beryllium being the leftmost element.
Exercise
1.) 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.
(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.
Ans 1- c) the atoms lose their electrons more easily
Reason: the atoms gain the electrons more easily because of high Z.effective.
2.) 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) AI (d) Si
Ans2- b) Mg
Reason: The formula given is XCl2 i.e the valency of ‘X’ atom is 2 . So, Na has 1 valency, Mg has 2, Al has 3 and Si has 4 valency.
3.) Which element has
(a) two shells, both of which are completely filled with electrons?
a) Neon
Reason: It contains two shells K &L which is completely filled having an electronic configuration of 2, 8
(b) the electronic configuration 2, 8, 2?
b) Magnesium
Reason: Atomic no. is 12 i.e EC is 2, 8, 2
(c) a total of three shells, with four electrons in its valence shell?
c) Silicon (Si)
Reason: Electronic configuration is 2, 8, 4 i.e 4 electrons in outermost orbit
(d) a total of two shells, with three electrons in its valence shell?
d) Boron
Reason: two shells K& L. The EC is 2, 3 i.e atomic number is 5.
(e) twice as many electrons in its second shell as in its first shell?
e) Carbon
Reason: EC- 2, 4 i.e twice as many electrons in its second shell as in first shell.
4.) (a) What property do all elements in the same column of the Periodic Table as boron have in common?
Ans 4- a) All have same valency i.e 3
Eg: B- 2, 3
Al- 2, 8, 3
(e) What property do all elements in the same column of the Periodic Table as fluorine have in common?
b) All have same valency i.e -1
Eg. F- 2,7
Cl- 2, 8, 7
Alternative Answer –
a.) Boron it is an metalloid which takes place 5th place in the periodic table, which means its atomic number is 5 and its atomic symbol is B. In periodic table boron takes place at 13th column or 13th group and 2nd row or 2nd period. In the 13th group there are 6 elements in which only boron is metalloid and remain 5 elements are metals but all 6 elements are have same valence electron which is 3.
b.) Fluorine it is an non metal element which takes place 9th place in the periodic table which means its atomic number is 9 and its atomic symbol is F. When we notice the periodic table fluorine takes place 2nd row or 2nd period and 17th group or 17th column. In this column there are 6 elements which are highly electronagetive and all have the capacity attract electron to complete their shell. In the 17th group all elements are non metals and all have same valence electrons which is 7.
5.) An atom has electronic configuration 2, 8, 7.
(a) What is the atomic number of this element?
Ans 5- a) The atomic number is 17 as it electronic configuration given is 2, 8, 7
(b) To which of the following elements would it be chemically similar? (Atomic numbers are given in parentheses.) N(7) F(9) P(15) Ar(18)
b) F(9)
Reason: Atomic no. 17 i.e atom is Chlorine means halogen group. So, other member will also be a halogen. Therefore, fluorine.
Alternative Answer –
- Given that the electronic configuration of the atom is 2 ,8 ,7
It means K = 2. L = 8. M = 7
w.k.t Atomic number = electrons in K shell + electrons in L shell + electrons in M shell +……….
Atomic number = K + L + M
= 2 + 8 + 7
Atomic number = 17
Which is Cl or Chlorine.
- Next to find an electron which is chemically similar to the chlorine.
We notice that chlorine has 7 valence electron in outermost shell therefore we find an element which is also has 7 valence electron in its outermost shell that is Fluorine it has total 9 electron in which first shell has 2 electron and second shell has 7 valence electron which is chemically similar to chlorine.
6.) The position of three elements A, B and C in the Periodic Table are shown below – Group 16 Group 17 – – – A – – B C
(a) State whether A is a metal or non-metal.
(b) State whether C is more reactive or less reactive than A.
(c) Will C be larger or smaller in size than B?
(d) Which type of ion, cation or anion, will be formed by element A?
Ans 6- a) A is a non- metal as it is given in Group 17 i.e p block elements. Generally, p- block elements are non- metals.
b) C is less reactive than A because as we go down the group the reactivity decreases.
c) C is smaller than B as moving across a period the Z.effective increases. So electrons tends to come closer to the nucleus.
d) A will form anion as it will gain 1 electron from other element to fulfil its octet.
Alternative Answer –
- A is an non metal.
- C is less reactive than A.
- C is smaller in size then B.
- Anion will be formed by element A.
7.) 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 7- Nitrogen- 2, 5 ; Phosphorus- 2, 8, 5
- Nitrogen will be more electronegative element than phosphorus because Shells are add up as we go down the group. So nuclear force decreases, size increases. The tendency to attract electrons toward the nucleus decreases. Therefore, electronegativity decreases while going down the group.
Alternative Answer –
We know that K shell has maximum 2 electron and L shell has maximum 8 electrons.
Now nitrogen ( atomic number 7 ) has 7 electrons in that K has 2 electron and next shell L has remain 5 electrons.
Generally we represent electron configuration in the form of electronic configuration (K,L,M)
Therefore electronic configuration of nitrogen is 2,5
And the shell of phosphorus ( atomic number 25 ) has 15 electron in that K has 2 electron and next shell L has 8 electrons and M shell has remain 5 electrons then we can write electronic configuration of phosphorus is 2 ,8,5
Phosphorus has big size of atomic radius then nitrogen and compair to size of atom nitrogen will be smaller than phosphorus. Both are non metals in which attraction of incoming electron towards the nuclear is very high in nitrogen comparing to phosphorus. In this reason we can say that the element nitrogen will be more electronagetive then the phosphorus.
8.) How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
Ans 8- Electronic configuration indirectly tell us the atomic number of the element. In modern periodic table, elements are arranged according to a atomic number. Same Valence electrons elements are arranged in same groups.
Alternative Answer –
An modern periodic table has 7 horizontal rows called periods and 18 vertical columns called groups. When we notice elements in rows it represent how many shelles have the elements for example Hydrogen (1) and lithium (3), the hydrogen is present in first row which represent hydrogen has only one shell whereas lithium present in second row which represent lithium has 2 shells. Further when we notice that elements in groups or each column it represents that how many electrons in valence shell. For example Boron (5) and Aluminium (13) , Boron and Aluminium are present in same group and both are having same electron in valence shell that is 5. In this reason electronic configuration of an atom relate to its position in the modern periodic table.
9.) 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?
Ans 9 – The element of atomic number 12 have the same chemical properties as calcium because both have same valence electrons in the outermost shell and thus having the same valency of +2.
Alternative Answer –
In an periodic table calcium is takes place in second column or second group and it is placed in the 4th row or 4th period we notice that calcium has 4 shells with 2 valence electron in outermost shell. After we notice that atomic number 12 and 38 which is magnesium and strontium both elements are placed in same group which is 2nd group therefore both elements are have 2 valence electron in outermost shell and the atomic number 19 and 21 which is potassium and scandium are placed in same row which means both have same shell number which means both have 4 shells but atomic number 19 has 1 valence electron and atomic number 21 has 3 valence electron. Therefore we can say that the atomic number 12 and 38 which have same valence electrons in outermost shell have physical and chemical properties resembling calcium.
10.) Compare and contrast the arrangement of elements in Mendeléev’s Periodic Table and the Modern Periodic Table.
Ans 10-
Mendeleev periodic table |
Modern periodic table |
Elements are arranged according to the atomic mass. |
Elements are arranged according to the atomic number. |
Groups for noble gases are not present. |
Given separate slot for noble gas in periodic table |
Total 8 groups were present. |
Total 18 groups are present. |
Has 12 horizontal rows called as periods. |
Has 7 periods in periodic table. |
Alternative Answer –
Mendeléev’s Periodic Table | Modern Periodic Table |
1. It has 8 groups or 8 columns. | It has 18 groups or 18 columns |
2. It has 6 rows or 6 periods. | It has 7 rows or 7 periods. |
3. In this periodic table every group contains its sub group. | In this periodic table there are no sub groups. |
4. Elements are arranged in the basis of atomic masses. | Elements are arranged in the basis of atomic numbers. |
5. In this periodic table nobel gases are not included because the nobel gases are not discovered. | In this periodic table nobel gases are have their separate group that is 18th column. |