CBSE Class 10 Chemistry Periodic Classification of Elements Worksheet Set A

MCQ Questions for NCERT Class 10 Science Periodic Classification of Elements

Question. Out of Li and Be which has higher ionisation energy?
(a) Li
(b) Be
(c) Both have same
(d) None

Answer: A

Question. The outermost shell for elements of period 2 will be:
(a) K shell
(b) L shell
(c) M shell
(d) N shell

Answer: B 

Question. The elements A, B and C belong to group 2, 14 and 16 respectively, of the periodic table. Which two elements of these will form covalent bonds?
(a) A and B
(b) B and C
(c) C and A
(d) None of these

Answer: B

Question. Where would you locate the element with electronic configuration 2,7 in the Modern Periodic Table?
(a) Group 8
(b) Group 9
(c) Group 18
(d) Group 10

Answer: B

Question. An element ‘X’ is forming an acidic oxide. Its position in modern periodic table will be:*
(a) Group 1 and Period 3
(b) Group 2 and Period 3
(c) Group 13 and Period 3
(d) Group 16 and Period 3

Answer: D

Question. State one reason for placing Mg and Ca in the same group of the periodic table.
Answer: They have same number of valence electrons.

Question. Explain why the number of elements in third period is 8?
Answer: 3rd shell can have maximum eight electrons if it is valence shell. Therefore, number of elements are equal to 8 in third period.

Question. Write the number of horizontal rows in the modem periodic table. What are these rows called? 
Answer: There are seven horizontal rows in the modem periodic table. These rows are called periods.

Question. Write the atomic numbers of two elements ‘X” and ‘ Y’ having electronic configurations 2, 8, 2 and 2, 8, 6 respectively. 
Answer: Atomic number of X = 2 + 8 + 2 = 12
Atomic number of Y = 2 + 8 + 6=16

Question. Give reason why noble gases are placed in separate group in modem periodic table. 
Answer: They have completely filled outermost shell.

Question. What was the basis of Mendeleev’s Periodic Law?
Answer: Increasing order of atomic weight.

Question. On moving from left to right in the second period when happens to the number of valence electrons?
Answer: Number of valence electrons increases from left to right in the second period.

Question. Give one example of such triads.
Answer: Li(7), Na(23), K(39)

Question. An element has atomic number 17 to which group and period closer it belong. 
Answer: Its electronic configuration is 2, 8, 7. It belongs to group 17 because it has 7 valence electrons. It belongs to 3rd period because it has 3 shalls.

Question. H, Li. Na, K placed in group. Why?
Answer: Tt is because they have same number of valence electron i.e. 10

Question. Why was the system of classification of elements into triads not found suitable?
Answer: It is because all the elements discovered at that time could not be classified into triads.

Question. What was the basis of Modem Periodic Law?
Answer: Atomic number

Question. What was the basis of classification of elements by Newland?
Answer: Increasing order of atomic mass

Question. What was need of classification of elements?
Answer: Classification of elements is needed to ‘more the study of elements every, e.g. elements of same group have similar properties study of a large number of elements is reduced to few group of elements.

Question. What was the earliest attempt to classify elements?
Answer: They were classified into metals and non-metals.

Question. Write the number of vertical columns in the modem periodic table. What are these columns called?
Answer: There are 18 vertical columns in the modem periodic table. These vertical columns are called groups.

Question. Which has larger atomic radius Ca (20) or K (19). 
Answer: K (19) has larger atomic radius due to less effective number charge.

Question. What is Newlands’ law of octaves? Explain with an example.
Answer: According to this law, when elements are arranged in the order of increasing atomic masses, the properties of the eighth element (starting from a given element) are a repetition of the properties of the first element.
For example: Lithium shows similarity with sodium.

Question. State Mendeleev’s periodic law. Write two achievements of Mendeleev’s periodic table.
Answer: Mendeleev’s Periodic Law states that ‘Properties of elements are the periodic function of their atomic masses.
Achievements :
(a) It could classify all the elements discovered at that time and helped in the discovery of new elements
(b) It helped in correction of atomic mass of some of the elements.

Question. Answer the following questions:
(i) In Mendeleev ’s periodic table the elements were arranged in the increasing order of their atomic masses. However, cobalt with atomic mass of 58.93 amu was placed before nickel
having an atomic mass of 58.71 amu. Give reason for the same.
(ii) In the classification of the then known elements, Mendeleev was guided by two factors. What are those two factors?
Answer: (i) This is done so that the elements with similar properties could be grouped together. Therefore, to arrange elements with similar properties together, cobalt is placed before Nickel neglecting its atomic mass.
(ii) The two factors are as follows:
(a) Increasing atomic masses.
(b) Grouping together of elements having similar properties.

Question. Use Mendeleev’s periodic table to predict the formulae for the oxides of the following elements: K, C, Al, Si, Ba.
Answer: K belongs to group 1. Therefore, the oxide will be K2O.
C belongs to group 4. Therefore, the oxide will be CO2.
Al belongs to group 3. Therefore, the oxide will be Al2O3.
Si belongs to group 4. Therefore, the oxide will be SiO2.
Ba belongs to group 2. Therefore, the oxide will be BaO.

Question. State the following:
(i) Write the formulae of chlorides of Eka-silicon and Ekaaluminium.
(ii) Write the number of elements in 2nd and 5th period in Modern Periodic Table?
(iii) Write the number of a group in which metallic, metalloid and non-metallic, all three types of elements, are present.
(iv) Write the number of horizontal rows in the modern periodic table. What are these rows called?
(v) Write the number of vertical columns in the modern periodic table. What are these columns called?
(vi) Write the formula used to determine the maximum numbers of electrons which a shell in an atom can accommodate?
Answer: (i) GeCl4, GaCl3
(ii) 2nd period has 8 elements, 5th period has 18 elements.
(iii) Group 14.
(iv) There are seven horizontal rows in the modern periodic table.
These rows are called periods.
(v) There are 18 vertical columns in the modern periodic table.
These are known as groups.
(vi) 2n2, where n is the number of shell.

Question. Can the following groups of elements be classified as Dobreiner’s triad?
(a) Na, Si, Cl, (b) Be, Mg, Ca.
Atomic mass of Be 9; Na 23; Mg 24; Si 28; Cl 35; Ca 40 Explain by giving reason.
Answer: (a) Na, Si, Cl cannot be classified as Dobereiner’s triad because here the elements do not belong to the same group and have different electronic configuration.
Na–2, 8, 1; Si–2, 8, 4 and Cl–2, 8, 7
(b) Be, Mg, Ca are the elements of Dobereiner’s triad because the mass of Mg is the arithmetic mean of the other two elements.
i.e., Be and Ca = 9 + 40/2 = 24.

Question. Which element has:
(i) two shells, both of which are completely filled with electrons?
(ii) the electronic configuration 2, 8, 2?
(iii) a total of three shells, with four electrons in its valence shell?
(iv) a total of two shells, with three electrons in its valence shell?
(v) twice as many electrons in its second shell as in its first shell?
Answer: (i) Neon has two shells, both of which are completely filled with
electrons (2 electrons in K shell and 8 electrons in L shell).
(ii) Magnesium has the electronic configuration 2, 8, 2.
(iii) Silicon has a total of three shells, with 4 electrons in its valence shell (2 electrons in K shell, 8 electrons in L shell and 4 electrons in M shell).
(iv) Boron has a total of two shells, with three electrons in its valence shell (2 electrons in K shell and 3 electrons in L shell).
(v) Carbon has twice as many electrons in its second shell as in its first shell (2 electrons in K shell and 4 electrons in L shell).

Question. How could the Modern periodic table remove various anomalies of Mendeleev’s periodic table?
Answer: Modern periodic table removes various anomalies of Mendeleev’s periodic table on the following points :
(a) Position of isotopes : As Modern periodic table is based on atomic number, isotopes can be placed at one place in same group in modern periodic table.
(b) Anomalous position of some pair of elements: In Mendeleev periodic table, some of the elements having higher atomic mass are placed before the elements having lower atomic mass. This defect of Mendeleev periodic table was overcome in Modern periodic table since it is based on atomic numbers.
(c) Prediction of new elements : In long form of periodic table, the position and properties of new elements can be predicted easily on the basis of their atomic numbers or electronic
configuration.

Question. Answer the following questions:
(i) What is the basic difference in approach between Mendeleev’s periodic law and the Modern periodic law?
(ii) In between nitrogen and oxygen; whose ionisation energy is high and why?
Answer: (i) The basic difference in approach between Mendeleev’s periodic law and Modern periodic law is the change in basis of classification of elements from atomic weight to atomic
number.
(ii) The electronegativity of N is greater than O because Nitrogen has stable and exactly half-filled p-orbitals.

Question. An element X of group 15 exists as diatomic molecule and combines with hydrogen at 773 K in presence of the catalyst to form a compound, ammonia which has a characteristic pungent smell.
(i) Identify the element X. How many valence electrons does it have?
(ii) Draw the electron dot structure of the diatomic molecule of X. What type of bond is formed in it?
(iii) Draw the electron dot structure for ammonia and what type of bond is formed in it?
Answer: (i) Nitrogen (atomic no. 7). Its electronic configuration is 2, 5; it has 5 valence electrons. 

Long Answer Type Questions :

Question. Answer the following questions:
(i) List any three observations which posed a challenge to Mendeleev’s Periodic law.
(ii) How does the metallic character of elements vary on moving from
(a) left to right in a period, 
(b) from top to bottom in a group of the Modern Periodic Table? Give reason for your answer.
Answer: (i) Three observations which posed a challenge to Mendeleev’s Periodic law are:
(a) The position of isotopes could not be explained.
(b) Wrong order of atomic masses of some elements could not be explained.
(c) A correct position could not be assigned to hydrogen in the periodic table.
(ii) (a) On moving from left to right in a period, the metallic character of elements increases because electropositive character decreases.
(b) On going down in a group of the periodic table, the metallic character of elements increases because electropositive character of elements increases.

Question. The electronic configuration of three elements A, B and C is given below:
A = 2. B = 2, 6 C = 2, 8, 2
(i) Which element belongs to the second period?
(ii) Which one of them is a noble gas?
(iii) What is the valency of B?
(iv) Name the element C.
(v) Which is a metal?
Answer: (i) B belongs to second period as its valency is two.
(ii) A( 2 = helium) is a noble gas.
(iii) 2 (8-6).
(iv) Magnesium (At. No. 12)
(v) C is a metal.

Question. By giving reasons state which amongst the given below elements does not belong to the same period.
6P12, 7Q14, 8R16, 11S23
Answer: The electronic configuration of the elements is given as: 

Element P, Q and R have only two electron shells and hence, they belong to the same period i.e., 2nd period.

Question. The elements A, B and C belong to groups 1, 14 and 17 respectively of the periodic table.
(i) Which two elements will form a covalent compound?
(ii) Which two elements will form an ionic compound?
(iii) Noble gases do not react with other elements. Why?
(iv) Atom is electrically neutral but still it has a tendency to form an ion. Why?
Answer: (i) B and C, will form covalent compounds since both are non-metals.
(ii) A and C will form on ionic compound since A is an alkali metal and C is non-metal.
(iii) Elements react in order to complete its octet. Noble gases have complete octet. Therefore, they do not react with other elements.
(iv) The elements have valence electrons. Metals have less valence electrons and give out the valence electrons to form cations to complete the outermost shell and attain nearest
noble gas configuration. Likewise, non metals attain electrons to form anions to complete the outermost shell and attain nearest noble gas configuration.

Question. The electrons in the atoms of four elements A, B, C and D are distributed in three shells having 1, 3, 5 and 7, electrons respectively in their outermost shells. Write the group numbers in which these elements are placed in the Modern Periodic Table.
Write the electronic configuration of the atoms of B and D, and the molecular formula of the compound formed when B and D combine.
Answer: A—1st group.
B—13th group.
C—15th group.
D—17th group.
Electronic configuration
B ⟶ Atomic number = 13
K L M
2 8 3
D ⟶ Atomic number = 17
K L M
2 9 7
The molecular formula of the compound when B and D combine is BD3.

Question. Answer the following questions:
(i) What is a group in the periodic table? In which part of a group would you separately expect the elements to have : (a) the greatest metallic character, (b) the largest atomic size?
(ii) In what respects do the properties of group 1 elements differ from those of group 17 elements?
(iii) From the stand point of atomic structure, what determines which element will be the first and which is the last in a period of the periodic table?
(iv) Explain why, the properties of elements are repeated after 2, 8, 18 and 32 elements in the periodic table.
(v) What are the advantages of the periodic table?
Answer: (i) The vertical columns in a periodic table are called groups.
(a) The greatest metallic character is found in the elements in the lowest part of the group.
(b) The largest atomic size is found in the lowest part of the group.
(ii) Group 1 elements have 1 valence electron and are ionic in chemical reactions, whereas, the elements of group 17 have 7 valence electrons. They all are non-metals.
(iii) The number of valence electrons in the atoms of elements decides which element will be the 1st element in a period and which will be the last in a period.
(iv) The properties of elements are repeated after 2, 8, 18 and 32 elements in the periodic table because the electronic configurations of the elements are repeated in this manner.
(v) Advantages of the periodic table:
(a) It is easier to remember the properties of an element if its position in the periodic table is known.
(b) The type of compounds formed by an element can be predicted by knowing its position in the periodic table.

Question. Atoms of eight elements A, B, C, D, E, F, G and H have the same number of electronic shells but different number of electrons in their outermost shell. It was found that elements A and G combine to form an ionic compound. This compound is added in a small amount to almost all vegetable dishes during cooking. Oxides of elements A and B are basic in nature while those of E and F are acidic. The oxide of D is almost neutral.
Based on the above information answer the following questions:
(i) To which group or period of the Periodic Table do the listed elements belong?
(ii) What would be the nature of compound formed by a combination of elements B and F?
(iii) Which two of these elements could definitely be metals?
(iv) Which one of the eight elements is most likely to be found in gaseous state at room temperature?
(v) If the number of electrons in the outermost shell of elements C and G be 3 and 7 respectively, write the formula of the compound formed by the combination of C and G.
Answer: (i) A and B belong to group 1 and 2 because they form basic oxides. C belongs to group 13 as it has 3 valence electrons. D belongs to group 14 as it forms almost neutral oxide. E and F belong to group 15 and 16 as they form acidic oxides, G belongs to group 17 as it has 7 valence electrons and H belongs to group 18. They belong to 3rd period of the periodic table because AG is NaCl, added in a small amount to almost all vegetable dishes during cooking and Na and Cl belong to 3rd period.
(ii) Ionic compounds will be formed because ‘B’ is metal and ‘F’ is non-metal. ‘B’ can lose two electrons and ‘F’ can gain two electrons.
(iii) A and B are definitely metals as they form basic oxides.
(iv) G and H are in gaseous state at room temperature.
(v) CG3 is the formula of the compound formed by combination of C and G.

Question. Answer the following questions:
(i) The modern periodic table has been evolved through the early attempts of Dobereiner, Newland and Mendeleev. List one advantage and one limitation of all three attempts.
(ii) Name the scientist who first of all showed that atomic number of an element is a more fundamental property than its atomic mass.
(iii) State Modern Periodic law.
Answer: (i) (a) Dobereiner:
Advantage: Group three elements having similar properties they were called as the Dobereiner triads. He arranged them in order of increasing atomic mass and the mass of middle element was equal to the average of the other two elements.
Limitation: He was able to identify only 4 traids but he failed in his attempt to group nitrogen, phosphorus and arsenic because atomic mass of phosphorus is not the average of other two.
(b) Newland:
Advantages: He arranged the elements in horizontal rows in order of increasing in atomic mass. The property of every 8th element was similar to the 1st element.
Limitation: His arrangement was only applicable to lighter elements.
(c) Mendeleev:
Advantage: He arranged the elements in order of there increasing atomic mass and he corrected the mass of beryllium from 4.5 to 13.5 u.
Limitation: Position of hydrogen and isotopes were not justified in his periodic table.
(ii) Henry Moseley showed that atomic number of an element is a more fundamental property than its atomic mass.
(iii) Modern periodic law states that “the properties of elements are the periodic function of their atomic number. Repetition of properties is due to the same outer electronic configuration.”

Question. Explain the periodicity of following properties of elements:
(i) Atomic radius
(ii) Ionisation enthalpy
Answer: (i) Atomic radius: In a period, atomic radius generally decreases from left to right. In a period there is a gradual increase in the nuclear charge. Since valence electrons are added in the same shell, they are more and more strongly attracted towards nucleus. This gradually decreases atomic radii. Atomic radii increase in a group from top to bottom. As we go down a group the number of shells increases and valence electrons are present in higher shell and the distance of valence electrons from nucleus increases. Both the factors
decrease the force of attraction between nucleus and valence electron. Therefore, atomic size increases on moving down a group.
(ii) Ionisation enthalpy: Ionisation energy decreases in a group from top to bottom. This is due to the fact that the force of attraction between valence electrons and nucleus decreases
in a group from top to bottom. Thus, less energy is required to remove electron from atom. On the either hand, the force of attraction between valence electron and nucleus increases
in a period from left to right. As a consequence of this, the ionisation energy increases in a period from left to right.
(iii) Electronegativity: Electronegativity is relative tendency of a bonded atom to attract the bond-electrons towards itself.
Electronegativity decreases in group from top to bottom. In a period, electronegativity increases from left to right because atomic size decreases.

Question. List the merits and demerits of Mendeleev periodic table.
Answer: Merits of Mendeleev periodic table:
(a) At some places the order of atomic weight was changed in order to justify the chemical and physical nature.
(b) Mendeleev left some gap for new elements which were not discovered at that time.
(c) One of the strengths of Mendeleev’s periodic table was that, when inert gases were discovered they could be placed in a new group without disturbing the existing order.
Demerits of Mendeleev periodic table:
(a) Position of hydrogen: Hydrogen resembles alkali metals (forms H+ ion just like Na+ ions) as well as halogens ( forms H– ion similar to Cl– ion).Therefore, it could neither be placed
with alkali metals (group I) nor with halogens (group VII ).
(b) Position of isotopes: Different isotopes of same elements have different atomic masses, therefore, each one of them should be given a different position in the periodic table. On
the other hand, because they are chemically similar, they had to be given same position.
(c) Anomalous pairs of elements: At certain places, an element of higher atomic mass has been placed before an element of lower atomic mass. For example, Argon (39.91) is
placed before potassium (39.1).

Creating Based Question :

Question. Question number 194(i)-194(iv) are based on table given below.
Study the table and answer the following questions. 

(i) What is valency of oxygen ?
(ii) Give the chemical formula formed by hydrogen and oxygen.
(iii) What is the electron dot structure of above formed compound in (ii) part ?
(iv) What is the chemical formula for element H, F used for bond formation ?
(a) H2F
(b) HF
(c) HF2
(d) HF3
Answer: (i) Valency of oxygen is 2.
(ii) 2H + O → H2O
1 2, 6
The chemical formula formed is H2O. 

(iii)
(iv) (b) HF.

Question. The position of eight elements in the modern periodic table is given below with atomic numbers. 

Answer the following question with reference to the above table.
(i) Write the electron configuration of Calcium (Ca).
(ii) Predict the number of valence electrons in Strontium (Sr).
(iii) What is the number of shells in Rubidium (Rb)?
(iv) Predict whether K is a metal or a non-metal?
Answer: (i) Electronic configuration of Calcium is 2, 8, 8, 2.
(ii) The number of valence electrons in Strontium (Sr) is 2.
(iii) The number of shells in Rubidium (Rb) is 5.
(iv) Potassium (K) is a metal, which has one valence electron.

Question. Consider the following elements, A, B, C and D in the given periodic table : 

(i) Which element is the most electronegative element ?
(ii) Which element is the most unreactive ?
(iii) Which element forms acidic oxides ?
(iv) Which element has 6 electrons in outer orbital ?
Answer: (i) Element B would be the most electronegative element.
(ii) Element D would be the most unreactive element.
(iii) Element B and C forms acidic oxides.
(iv) Element A has 6 electrons in outer orbital.

Question. Write the contrasting points present in modern periodic table, against the following given points of Mendeleev’s table :
(i) Elements arranged according to atomic mass.
(ii) It has 8 groups and 6 periods.
Answer: The contrast points can be written as :
(i) In modern periodic table the elements are arranged according to atomic number.
(ii) Modern periodic table has 18 groups and 7 periods.

Question. Based on the table given below answer the following questions: 

(i) What is the electronic configuration of F?
(ii) What is the number of valence electrons in the atom of F?
(iii) Write the size of the atoms of E, F, G and H in decreasing order.
(iv) Out of B, E and F which one has the biggest atomic size?
Answer: (i) ‘F’ has electronic configuration 2, 8, 2.
(ii) ‘F’ has two valence electrons.
(iii) H > G > F> E is decreasing order of size of atoms.
(iv) ‘B’ is having biggest atomic size among B, E and F.

Question. 

(i) What is the electronic configuration of F?
(ii) What is the number of valence electrons in the atom of F?
(iii) Write the size of the atoms of E, F, G and H in decreasing order.
(iv) Out of B, E and F which one has the biggest atomic size?
Answer: (i) ‘F’ has electronic configuration 2, 8, 2.
(ii) ‘F’ has two valence electrons.
(iii) H > G > F> E is decreasing order of size of atoms.
(iv) ‘B’ is having biggest atomic size among B, E and F.

Question. An element X forms a chloride with the formula XCl2, which is a solid with a high melting point. Predict the most likely outer orbital electronic configuration of X and also name two more elements from same group of the Periodic Table to which elements X belongs.
Answer: The element X has 2 electrons in outer orbital as it forms a dichloride (XCl2). So, this element belongs to group 2 of periodic table. Other elements of group 2 are magnesium (Mg) and beryllium (Be).

Question. Oxygen (atomic number 8) and sulphur (atomic number 16) belong to group 16 of the periodic table. Write the electronic configuration of the two elements. Which of them will be more electronegative ? Why ?
Answer: Oxygen has atomic number 8, electronic configuration will be → 2, 6
Sulphur has atomic number 16, electronic configuration will be → 2, 8, 6
Oxygen with two shells will be more electronegative because it can easily gain electron due to its smaller size of atom, the nuclear charge attracts the electron easily to become negative ion.

Question. Consider the following elements, A, B, C and D in the given periodic table: 
(i) Which element is the most electronegative element?
(ii) Which element is the most unreactive ?
(iii) Which element forms acidic oxides ?
(iv) Which element has 6 electrons in outer orbital ?
Answer: (i) Element B would be the most electronegative element.
(ii) Element D would be the most unreactive element.
(iii) Element B and C forms acidic oxides.
(iv) Element A has 6 electrons in outer orbital.

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