Worksheets Chapter 5 Periodic Classification of Elements Class 10 Science

Students should refer to Worksheets Class 10 Science Periodic Classification of Elements Chapter 5 provided below with important questions and answers. These important questions with solutions for Chapter 5 Periodic Classification of Elements have been prepared by expert teachers for Class 10 Science based on the expected pattern of questions in the class 10 exams. We have provided Worksheets for Class 10 Science for all chapters on our website. You should carefully learn all the important examinations questions provided below as they will help you to get better marks in your class tests and exams.

Periodic Classification of Elements Worksheets Class 10 Science

MULTIPLE CHOICE QUESTIONS

Question. Identify the group which is not a Döbereiner triad
(a) Li, Na, K
(b) Be, Mg, Cr
(c) Ca, Sr, Ba
(d) Cl, Br, I

Question. An element has an atomic number of 15 with which of the following elements will it show similar chemical properties?
(a) Be(4)
(b) Ne(10)
(c) N(7)
(d) O(8)

Question. The increasing order of the atomic radii of elements Na, Rb, K, Mg is
(a) Na < K < Mg < Rb
(b) K < Na < Mg < Rb
(c) Na < Mg < K < Rb
(d) Mg < Na < K < Rb

Question. The element with atomic number 3 to 10 belong to the second period. Identify the most electropositive and most electronegative element.
(a) F, Li
(b) Li, F
(c) Li, Ne
(d) Ne, Li

Question. Which of the following sets does not belong to a group?
(a) Li, Na, K
(b) B, C, N
(c) B, Al, Ga
(d) O, S, Se

Question. Which of the following is not the characteristics of isotopes of an element?
Isotopes of an element
(a) show same atomic mass
(b) show same atomic number
(c) occupy same position in the Periodic Table
(d) show same chemical properties

Question. An element with atomic number will form a basic oxide _________.
(a) 7
(b) 17
(c) 14
(d) 11

Question. Element belonging to which of the following atomic numbers 11, 19, 14, 18, 23 belong to the same period?
(a) 11, 14, 23
(b) 11, 18, 20
(c) 11, 14, 18
(d) 14, 19, 23

Question. Arrange the following elements into the increasing order of their metallic character along a period.
(a) S < Si < P < Al
(b) S < P < Si < Al
(c) Si < P < S < Al
(d) Si < S < P < Al

Question. The correct order of the increasing radii of the elements Na, Si, Al and P is
(a) Si, Al, P, Na
(b) P, Si, Al, Na
(c) Al, Si, P, Na
(d) Al, P, Si, Na

Question. The group number and period number respectively of an element with atomic number 8 is
(a) 6, 2
(b) 16, 2
(c) 6, 8
(d) 16, 4

Question. Which is not true about noble gases?
(a) They are non-metallic in nature
(b) They exist in atomic form
(c) They are radioactive in nature
(d) Xenon is the most reactive among these

Question. Which of the given elements A, B, C, D, and E with atomic number 3, 11, 15, 18, 19 respectively belong to the same group
(a) A, B, C
(b) B, C, D
(c) A, D, E
(d) A, B, E

Question. In the Modern Periodic Table, the metals among the first ten elements are—
(a) Be, Na
(b) Li, Be
(c) Be, Li, Na
(d) Li, Na

Question. An element belongs to period 2 and group 2 the number of valence electrons in the atoms of this element is
(a) 2
(b) 4
(c) 3
(d) 1

Question. Identify the wrong sequence of the elements in a group
(a) Ca, Sr, Ba
(b) Cu, Au, Ag
(c) N, P, As
(d) Cl, Br, I

Question. Two elements X and Y have —
(i) X has 17 protons 18 neutrons
(ii) Y has 17 protons and 20 neutrons Both X and Y are—
(a) Isobars
(b) Isotopes
(c) Isotones
(d) None of the above

Question. Mendeleev predicted the existence of two elements and named them as eka-silicon and eka-aluminium. Identify the elements which took their position at later stage
(a) Si and Ge
(b) Si and Ga
(c) Ge and Ga
(d) Si and Al

Question. 14 elements after actinium is called
(a) Lanthanides
(b) Actinides
(c) d-block elements
(d) p-block elements

Question. An element ‘X’ is placed in group 13 and third period of the Periodic Table. It burns in oxygen to form an oxide which is amphoteric in nature. Identify the chemical formula
of its chloride
(a) CCl₄
(b) BCl₂
(c) GaCl₃
(d) AlCl₃

Question. In the Modern Periodic Table calcium (Z = 20) is surrounded by the elements with atomic numbers 12, 19, 21, and 38 which of the following will have physical and chemical properties resembling calcium.
(a) 12, 20, 38
(b) 12, 19, 20, 38
(c) 19, 20, 38
(d) 12, 19, 20

Question. Electronic configuration of Al+3 is
(a) 2, 8, 3
(b) 2, 8, 8
(c) 2, 8
(d) 2, 8, 8, 3

Question. An element X (2, 8, 2) combines separately with (SO4)2–and (PO4)3– radicals. The chemical formulae of the compounds are
(a) X₂SO₄ : X₃(PO₄)₂
(b) XSO₄ : X₃(PO₄)₂
(c) X(SO₄)2 : X₂(PO₄)₃
(d) XSO₄ : X₃(PO4)₃

Question. Two elements X and Y belong to group 1 and 2 respectively in the same period. The formulae of this oxides are
(a) XO, YO
(b) X₂O, YO
(c) X₂O, Y₂O
(d) XO, YO₂

Question. Which of the following has maximum non-metallic character?
(a) F
(b) Br
(c) Cl
(d) I

Question. In the third period of the Periodic Table the element having smallest size is
(a) Na
(b) Ar
(c) Cl
(d) Si’

Question. According to Mendeleev’s periodic law the elements are arranged in the periodic table as per their.
(a) Increasing atomic number
(b) Increasing atomic mass
(b) Decreasing atomic number
(d) Decreasing atomic mass.

Question. Which of the following elements would lose an electron easily:
(a) Mg
(b) Ca
(c) K
(d) Cl₂

Question. Identify the metal with the electronic configuration 2,8,2
(a) Sodium
(b) Chlorine
(c) Magnesium
(d) Lithium

Question. Which of the following atoms has the smallest size;
(a) K(19)
(b) Na(11)
(c) B(5)
(d) C(6)

Question. Out of the elements given below which one of them is the most non-metallic;
(a) Fluorine
(b) Oxygen
(c) Chlorine
(d) Calcium

Question. Assertion. Silicon is a metalloid.
Reasons: Silicon shows only non-metallic properties.
(a) Both A and R are true and R is correct explanation for A.
(b) Both A and R are true and R is not the correct explanation for A.
(c) A is true but R is false.
(d) A is false but R is true.

Question. Assertion: Fluorine is more reactive than chlorine.
Reasons: Fluorine andchlorinebelong to the 17th group called Halogens .
(a) Both A and R are true and R is correct explanation for A.
(b) Both A and R are true and R is not the correct explanation for A.
(c) A is true but R is false.
(d) A is false but R is true.

Very Short Answer Type Questions :

Question. What were the criteria used by Mendeleev in creating his Periodic Table?
Answer: (i) Increasing order of atomic mass of the elements.

Question. In the Modern Periodic Table, which are the metals among the first ten elements.
Answer: Lithium and beryllium are metals.

Question. What were the limitations of Döbereiner’s classification?
Answer: (a) All the existing elements were not classified.
(b) Döbereiner could identify only three triads from the elements. Hence this system was not useful.

Question. Name two elements you would expect to show chemical reactions similar to magnesium.
What is the basis for your choice?
Answer: Calcium and barium.
Reason : (i) Both of them belong to same group as magnesium.
(ii) Ba and Ca has same valence electrons as Mg, and will show same properties as of magnesium.

Question. What were the limitations of Newlands’ Law of Octaves?
Answer: Newlands’ law was applicable only till calcium, after Ca, every eighth element did not possess properties similar to first.
New elements discovered did not fit into the law.
Wrong order of arrangement of elements was done, e.g. Co and Ni do not resemble halogen were found together in same slot, Fe being similar to Co and Ni was separated and kept in different slot.

Question. Besides gallium, which other elements have since been discovered that were left by Mendeleev in his Periodic Table? (any two)
Answer: Besides gallium, germanium and scandium have been discovered.
(ii) All elements in a group with similar properties.
(iii) The formula of oxides and hydrides formed by an element.

Question. Why do you think noble gases are placed in a separate group?
Answer: Noble gases are inactive, do not resemble other elements and all of them show same properties, hence they are grouped separately.

Question. By considering their position in the Periodic Table, which one of the following elements would you expect to have maximum metallic characteristics?
Ga, Ge, As, Se, Be
Answer: Among the given elements Be will show maximum metallic characteristics as it belongs to extreme left of the Periodic Table.

Question. How could the Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table?
Answer: Modern Periodic Table is based on the atomic number of elements, therefore
(i) problem of isotopes was solved because isotopes have same atomic number
(ii) wrong order of Ar, K, Co, Ni was removed.

Question. Did Döbereiner’s triads also exist in the columns of Newland’s Octaves? Compare and find out.
Answer: Yes, it exists in the Newland’s octave. It is Li, Na and K.

Question. 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.
Answer: (a) Li, Na, K
(2, 1) (2, 8, 1) (2, 8, 8, 1)
(b) Be, Mg
(2, 2) (2, 8, 2)
(c) He, Ne, Ar
(2) (2, 8) (2, 8, 8)

Question. (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?
Answer: (a) All these metals are highly reactive, they have same valence electrons i.e. 1 and can readily loose electrons to become positive ions.
(b) Helium and neon have completely filled outermost shell.

Question. Use Mendeleev’s Periodic Table to predict the formulae for the oxides of the following elements:

K, C, Al, Si, Ba 

Answer:

Element	Group No.	Formula
k	1	K2O
cl	4	CO2
Al	3	Al2O3
Si	4	SiO2
Ba	2	BaO

Question. 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
Answer: (b) Mg.

Short Answer Type Question :

Question. How does the electronic configuration of an atom relate to its position in the Modern Periodic Table? 
Answer: The position of element depends upon its electronic configuration. The number of shells is equal to the period number. The valence electrons decides the group number in which it will be, elements with 1 valence electrons belong to group 1.
Elements with 2 valence electrons belong to group 2.

Question. Which element has
(a) two shells, both of which are completely filled with electrons?
(b) the electronic configuration 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?
Answer: (a) Ne (2, 8) (b) Mg (2, 8, 2)
(c) Si (2, 8, 4) (d) B (2, 3)
(e) C (2, 4)

Question. (a) What property do all elements in the same column of the Periodic Table as boron have in common?
(b) What property do all elements in the same column of the Periodic Table as fluorine have in common?
Answer: (a) All other elements have same valence electrons and their valency is 3.
(b) All are non-metals, they have same valence electrons i.e., 7 and their valency is
1, all of them gain electrons to form negative ions.

Question. The position of three elements A, B and C in the Periodic Table are shown below: (img 59)
(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?
Answer: (a) ‘A’ is non-metal.
(b) ‘C’ is less reactive than ‘A’
(c) ‘C’ is smaller in size than ‘B’
(d) ‘A’ will form negatively charged ion — Anion

Question. 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?
(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.
Answer: (c) The atoms lose their electrons more easily.

Question. Nitrogen (atomic number 7) and phosphorous (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?
Answer: Nitrogen atomic number 7 → 2, 5
Phosphorus atomic number 15 → 2, 8, 5
Nitrogen 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. 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.
Answer: Ca atomic number — 20
Electronic configuration — 2, 8, 8, 2
Elements with atomic number 12 → 2, 8, 2
and atomic number 38 → 2, 8, 18, 8, 2
will resemble calcium as they all have same valence electrons and their chemical properties are also same.

Question. An atom has electronic configuration 2, 8, 7.
(a) What is the atomic number of this element?
(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)
Ans. (a) The atomic number of the element is 17.
(b) F(9) (2, 7) will be chemically similar to the given element.

Question. Compare and contrast the arrangement of elements in Mendeleev’s Periodic Table and the Modern Periodic Table.
Answer:  

Mendleev’s Periodic Table	Modern Periodic Table
1. It has 8 groups and 6 periods.	It has 18 groups and 7 periods.
2. Transition elements are not separated.	Transition elements are given separate place.
3. The inert gases were not present.	The inert gases are present in separate group.
4. Lanthanides and Actinides were not present.	Lanthanides and Actinides are at the bottom
5. Position of element i,e., group number and period number cannot be predicted.	Group number and period number can be predicted from its electronic configuration.

Question. Write the number of periods in the modern periodic table. State the changes in valency and metallic character of elements as we move from left to right in a period. Also state the changes, if any, in the valency and atomic size of elements as we move down the group.
Answer: 
There are 7 periods in Modern Periodic Table.
Valency first increases and then decreases. Metallic character decreases along a period from left to right.
There is no change in valency down the group.
Atomic size increases down the group.

Question. Two elements P and Q belong to the same period of the modern periodic table and are in Group-1 and Group-2 respectively. Compare their following characteristics in tabular form:
a. The number of electrons in their atoms.
b. The size of their atoms.
c. Their metallic character.
d. Their tendency to lose electrons.
e. The formula of their oxides.
f. The formula of their chlorides.
Answer: 
a. P has 1 valence electron, Q has 2 valence electrons.
b. P is bigger than Q.
c. P is more metallic than Q.
d. P can lose electrons more easily than Q.
e. P2O and QO
f. PCl and QCl₂

Question. Taking example of an element of atomic number 16, explain how the electronic configuration of the atom of an element relates to its position in the Modern Periodic Table and how valency of an element is calculated on the basis of its atomic number?
Answer: 
S(16) has electronic configuration of 2,8, 6, Group number = valence electrons + 10 = 6 + 10 = 16
Period number = Number of shells = 3 Valency = 8 – valence electrons =8-6=2

Question. Atomic radii of the elements of second period are given below:

a. Arrange them in decreasing order of their atomic size.
b. Are the elements now arranged in the pattern of a period in periodic table?
c. Which elements have the largest and the smallest atoms?
d. How does the atomic radius change as you go from left to right in a period.
Answer: 
a. Li > Be > B > C > N > O
b. Yes, They belong to the second period.
c. Li is the largest, oxygen is the smallest.
d. Atomic size decreases along a period from left to right.

Question. Describe the basic character of oxides of third period elements across the period from left to right.
Answer: 
Na₂O, MgO are basic oxides.
SiO₂, Al₂O₃ are amphoteric oxides.
P₂O₅, SO₂, Cl₂O₇ are acidic oxides.
Basic character of oxides decreases across the period.

Question. The atomic number of an element X’is 20.
a. Determine the position of the element “X’ in the periodic table.
b. Write the formula of the compound formed when ‘X’ reacts/combines with another element *Y’ (atomic number 8).
c. What would be the nature (acidic or basic) of the compound formed? 
Answer: 
X(20): 2, 8, 8, 2; Y(8): 2, 6
a. It belongs to group 2, 4th period because its valence electrons are 2 and no. of shells = 4

c. Compound formed will be basic because “X’ is a metal.

Question. a. State Modern Periodic Law
b. Elements A, B, C and D have atomic number 1, 8, 11, 19 respectively. Choose the odd element and give reason for your answer.
Answer: 
a. Modern Periodic Law: It states ‘properties of elements are a periodic function of their atomic number’.
b. B(8): 2, 6 is an odd element because it has 6 valence electrons whereas others have 1 valence electron.

Question. How does tendency to lose electrons change in the Modern Periodic Table in (a) a group, (b) a period and why?
Answer: 
a. In a group, tendency to lose electrons increases down the group because atomic size increases, forces of attraction between the valence electron and nucleus decreases.
b. In a period, tendency to lose electrons decreases due to decrease in atomic size due to more effective nuclear charge.

Question. a. Why did Mendeleev leave gaps in his periodic table?
b. State any three limitations of Mendeleev’s periodic table.
c. How do the electronic configuration of atoms change in a period with increase in atomic number.
Answer: 
a. He left gaps for the new elements which are to be discovered.
b. (i) Increasing order of atomic mass could not be maintained.
(ii) Position of hydrogen was not justified.
(iii) Isotopes could not be placed in different slots due to different atomic mass but same properties.
c. Number of valence electrons keep on increasing along a period from left to right in a period.

Question. In the periodic table, how does the tendency of atoms to lose electrons change on going from
a. left to right across a period?
b. top to bottom in a group?
Answer: 
a. Tendency to lose electron(s) decreases across the period from left to right.
b. Tendency to lose electron(s) increases down in a group.

Question. An element X belongs to 3rd period and group 16 of the Modern Periodic Table.
a. Determine the number of valence electrons and the valency of X.
b. Molecular formula of the compound when X reacts with hydrogen and write its electron dot structure.
c. Name the element X and state whether it is metallic or non-metallic.
Answer: 
a. X is sulphur, S(16): 2, 8, 6. It has 6 valence electrons. Its valency is equal to 2.
b. H₂X,

c. X is a non-metal.

Question. The electronic configuration of an element X is 2, 8, 8, 2. To which period and group of periodic table does the element X belong to? State the valency and justify your answer in each case.
Answer: 
It belongs to 4th period because it has four shells.
It belongs to group 2 because it has 2 valence electrons. X has a valency equal to 2 because it can lose 2 electrons to become stable.

Question. The position of elements A, B, C, D, E, F and G in the Modern Periodic Table is given as under:

a. In which group are inert elements placed?
b. What type of ions would ‘B’, ‘C’, ‘E’ and ‘F’will form?
c. Which element would have chemical properties similar to ‘C’?
d. How many shells do ‘A’ have?
e. What is the similarity between ‘A’ and ‘D’?
f. Identify the most abundant element in the earth crust.
Answer: 
a. Group 18
b. They will form anions.
c. F will have similar properties to ‘C’.
d. A has only one shell.
e. A and D both are inert elements.
f. C is the most abundant element in the Earth crust.

Question. The elements 4Be, 12Mg and 20Ca having two valence electrons in their valence shells are in periods 2, 3 and 4 respectively of the modern periodic table. Answer the following questions associated with these elements, giving reason in each case:
a. In which group should they be placed?
b. Which one of them is least reactive?
c. Which one of them has the largest atomic size?
Answer: 
a. They belong to group 2.
b. Be is least reactive.
c. Ca has largest atomic size.

Question. Three elements ‘X’, ‘Y’ and ‘Z’ have atomic numbers 7, 8 and 9 respectively.
a. State their positions (Group number and period number both) in the Modern Periodic Table.
b. Arrange these elements in decreasing order of their atomic radii.
c. Write the formula of the compound formed when X’ combines with ‘Z’.
Answer: 
X(7): 2, 5,
Y(8): 2, 6
Z(9): 2, 7
a. X belong to Group 15 and 2nd period.
Y belong to Group 16 and 2nd period.
Z belong to Group 17 and 2nd period.
b. X > Y > Z

Question. Four elements P, Q, R and S belong to third period of the Modern Periodic Table and have respectively 1, 3, 5 and 7 electrons in their outermost shell. Write the electronic configurations of Q and R and determine their valencies. Write the molecular formula of the compound formed when P and S combine.
Answer: 
P: 2, 8, 1 Valency = 1
Q: 2, 8, 3 Valency = 3
R: 2, 8, 5 Valency = 3
S: 2, 8, 7 Valency = 1
PS is the formula of compound.

Question. Arrange the following elements in descending order of their atomic size and give reason for your answer.
Mg(12), P(15), Cl(17), Ar(18)
Answer: 
Mg > P > Ar > Cl
As we move from left to right, atomic size decreases due to increase in effective nuclear charge. Ar is bigger than Cl due repulsion between 8 valence electrons.

Question. The position of three elements A, B and C in the Periodic Table is shown below:

Giving reasons, explain the following:
a. Element ‘A’ is a non-metal.
b. Element ‘B’ has a larger atomic size than element ‘C’.
c. Element ‘C’ has a valency of 1.
Answer: 
a. A is a non-metal because it has 7 valence electrons, it can gain one electron to form anion.
b. B has less electrons and protons, less forces of attraction between the nucleus and valence electrons, therefore it is bigger in size.
c. C can gain 1 electron to become stable, therefore its valency is equal to 1.

Question. Study the following table in which positions of six elements A, B, C, D, E and F are shown as they are in the modern periodic table:

On the basis of the above table, answer the following questions:
a. Name the element which forms only covalent compounds.
b. Which element is a metal with a valency of one?
c. Which element is a non-metal with a valency of two?
d. Out of D and E, which has a bigger atomic radius and why?
e. Write the formula of the compound formed when B combines with D.
Answer: 
a. E forms only covalent compounds.
b. D is a metal with valency of 1.
c. B is a non-metal with valency of 2.
d. D has bigger atomic size because it has less effective nuclear charge.

DB² is formula of the compound.

Question. Write the main aim of classifying elements. Name the basic property of elements which is used in the development of Modern Periodic Table. State the Modern Periodic Law. On which side (part) of the Modern Periodic Table do you find metals, metalloids and non- metals?
Answer:  Classification is done so as to study the properties of 118 elements easily. Modern periodic table is based on atomic number of the atom an element. ‘Properties of elements are a periodic function of their atomic numbers.’ Metals are placed on the left and middle, non-metals are placed on the right and Metalloids are placed on the border line between metals and nonmetals in a zig-zag manner.

Question. (a) Identify the element that have two completely filled shells and the number of valence electrons in each case if atomic numbers are: (i) 1, (ii) 2,(iii) 7, (iv) 8
(b) Analyse which amongst them is inert.
Answer : 
a. (i) 2, 8, 1: Sodium
(ii) 2, 8, 2: Magnesium
(iii) 2, 8, 7: Chlorine
(iv) 2, 8, 8: Argon
(b) Argon is inert.

Question. The atomic number of K and Ca is 19 and 20 respectively and they belong to same period.
a. Which amongst them would have smaller atomic size?
b. Which one would be more electro¬positive?
c. To which group would each one belong to?
Answer : 
a. Ca has smaller atomic size.
b. K is more electropositive.
c. K belongs to group 1, Ca belongs to group 2.

Question. The position of three elements A, B and C in the periodic table are indicated below:
Answer : Group 16 Group 17
– – (First Period)
– A (Second Period)
– – (Third Period)
B C Fourth Period)
a. State whether element C would be a metal or a non-metal. Why?
b. Which is the more active element, A or C? Why?
c. Which type of ion (cation or anion) will be formed
by the element C? Why?
Answer :
a. O is a non-metal because it has 7 valence electrons.
It can gain one electron to form an anion.
b. A is more reactive than C because it is smaller in size, therefore it can gain electron(s) easily.

Question. Atoms of seven elements A, B, C, D, E, F and G have a different number of electronic shells but have the same number of electrons in their outermost shells.
The elements A and C combines with chlorine to form an acid and common salt respectively. The oxide of element A is liquid at room temperature and it is a neutral substance, while the oxides of the remaining six elements are basic in nature. Based on the above information, answer the following question:
a. What could the element A be?
b. Will elements A to G belong to the same period or same group of the periodic table?
c. Write the formula of the compound formed by the reaction of the element A with oxygen.
d. Show the formation of the compound by the combination of element C with chlorine with the help of electronic structure.
e. What would be the ratio of number of combining atoms in a compound formed by the combination of element A with carbon?
f. Which one of the given elements is likely to have the smallest atomic radius?
Answer : 
a. A is hydrogen.
b. A and G will belong to the same group.
c. H2O is the formula of the compound.
d.

f. A has smallest atomic radius.

Question. In the following table, six elements A, B, C, D, E and F (here letters are not the usual symbols of the elements) of the Modern Periodic Table with atomic numbers 3 to 18 are given as follows:

3	4	5	6	7	8	9	10
A					E		G
11	12	13	14	15	16	17	18
B	C		D			F

a. Which of these is (i) a noble gas, (ii) a halogen?
b. If B combines with F, what would be the formula of the compound formed?
c. Write the electronic configurations of ‘C’and’E’.
Answer : 
a. (i) G is a noble gas, (ii) F is a halogen.
b. BF is the formula of compound.
c. C: 2, 8, 2 E: 2, 8, 6

Question. In the following table, are given eight elements A,B, C, D, E, F, G and H (here letters are not the usual symbols of the elements) of the Modem Periodic Table with the atomic numbers of the elements in parenthesis.   

Period	Group 1	Group 2
2	A(3)	E(4)
3	B(11)	F(12)
4	C(19)	G(20)
5	D(37)	H(38)

a. What is the electronic configuration of‘F?
b. What is number of valence electrons in ‘F’?
c. What is number of shells in *F’?
d. Arrange E, F, G, H in decreasing order of atomic size.
e. State whether F is a metal or a non¬metal.
f. Out of three elements B, E and F, which one has biggest atomic size.
Answer : a. 2, 8, 2 is the electronic configuration of F.
b. No. of valence electrons = 2.
c. Three shells are present in F.
d. H > G > F > E is the decreasing order of atomic size.
e. F is a metal.
f. B has biggest atomic size.

Question. a. Why did Mendeleev leave gaps in his periodic table?
b. State any three limitations of Mendeleev’s periodic table.
c. How do the electronic configuration of atoms change in a period with increase in atomic number.
Answer : 
a. He left gaps for the new elements which are to be discovered.
b. (i) Increasing order of atomic mass could not be maintained.
(ii) Position of hydrogen was not justified.
(iii) Isotopes could not be placed in different slots due to different atomic mass but same properties.
c. Number of valence electrons keep on increasing along a period from left to right in a period.

Question. a. What is meant by periodicity in properties of elements with reference to the periodic table?
b. Why do all the elements of the same group have similar properties?
c. How will the tendency to gain electrons change as we go from left to right across a period. Why?
Answer : 
a. The repetition of similar properties after regular intervals is called periodicity in properties.
b. It is because they have the same number of valence electrons.
c. Tendency to gain electrons increases from left to right across the period due to decrease in atomic size.

Question. The position of three elements A, B and C in the Periodic Table is shown below:

Group 16	Group 17
–	–
–	A
–	–
B	C

Giving reasons, explain the following:
a. Element ‘A’ is a non-metal.
b. Element ‘B’ has a larger atomic size than element ‘C’.
c. Element ‘C’ has a valency of 1.
Answer : 
a. A is a non-metal because it has 7 valence electrons, it can gain one electron to form anion.
b. B has less electrons and protons, less forces of attraction between the nucleus and valence electrons, therefore it is bigger in size.
c. C can gain 1 electron to become stable, therefore its valency is equal to 1.

Question. The position of three elements A, B and C in the Periodic Table is shown below: 

Group → Period ↓	1	2	13	14	15	16	17
1	B
2							A
3						C

Giving reasons, explain the following:
a. Element A is a non-metal.
b. Atoms of element C has a larger size than atoms of element A.
c. Element B has a valency of 1.
Answer :
a. A is a non-metal because it can gain one electrons to form anion.
b. C has more number of shells i.e., it has 3 shells because it belongs to 3rd period whereas A has 2 shells as it belongs to 2nd period.
c. B can lose 1 electron to become stable, therefore its valency is equal to 1.

Question. What physical and chemical properties of elements were used by Mendeleev in creating his periodic table? List two observations which posed a challenge to Mendeleev’s Periodic Law.
Answer : 
a. Increasing order of atomic mass was the physical property.
b. Formulae of oxides and hydrides was the chemical property.
i. Increasing order of atomic mass could not be maintained.
ii. Position of isotopes posed a challenge for the classification of elements.

Question. Table given below shows a part of the modern periodic table. 

H							He
Li	Be	B	C	N	O	F	Ne
Na	Mg	AI	Si	P	S	CI	Ar

Using this table, explain why
a. Li and Na are considered as active metals.
b. Atomic size of Mg is less than that of Na.
c. Fluorine is more reactive than chlorine.
Answer : 
a. Li and Na have largest atomic size in respective period, therefore they can lose an electron easily, hence they are active metals.
b. Mg has 12 protons and 12 electrons which has more forces of attraction, therefore, it is smaller in size than Na which is having 11 protons and 11 electrons.
c. F is smaller in size, it can gain electrons easily, therefore, it is more reactive than Cl.

Question. The elements 4Be, 12Mg and 20Ca having two valence electrons in their valence shells are in periods 2, 3 and 4 respectively of the modern periodic table. Answer the following questions associated with these elements,giving reason in each case:
a. In which group should they be placed?
b. Which one of them is least reactive?
c. Which one of them has the largest atomic size?
Answer : 
a. They belong to group 2.
b. Be is least reactive.
c. Ca has largest atomic size.

Question. The element Be, Mg and Ca are placed in the second group of the periodic table. Their atomic numbers are
4, 12, 20 respectively
a. Write the electronic configuration of these elements.
b. Write the valency exhibited by them,
c. Which three elements will be the most reactive?
Answer :
a.

Shell	K	L	M	N
Be(4) :	2	2
Mg(12) :	2	8	2
Ca(20):	2	8	8	2

b. Valency is 2.
c. Ca is the most reactive metal.

Question. As we move across a period in the periodic table, what is gradation in the following properties: (a) Atomic size, (b) Atomic number, (c) Electronegativity?
Answer : 
a. Atomic size goes on decreasing across the period from left to right.
b. Atomic number goes on increasing along the period from left to right.
c. Electronegativity goes on increasing along a period from left to right.

Question. (a) Name metals among the first five elements of the Modern Periodic Table.
(b) Write their symbols.
(c) Write the formula of their oxides.
Answer : 
a. Lithium and Beryllium are metals among first five elements.
b. Lithium (Li), Beryllium (Be).
c. Li2O and BeO are the formulae of their oxides.

Question. The position of elements A, B, C, D, E, F and G in the Modern Periodic Table is given as under:

Group → Period ↓	16	17	18
1			A
2	B	C	D
3	E	F	G

a. In which group are inert elements placed?
b. What type of ions would ‘B’, ‘C’, ‘E’ and ‘F’will form?
c. Which element would have chemical properties similar to ‘C’?
d. How many shells do ‘A’ have?
e. What is the similarity between ‘A’ and ‘D’?
f. Identify the most abundant element in the earth crust. 
Answer : 
a. Group 18
b. They will form anions.
c. F will have similar properties to ‘C’.
d. A has only one shell.
e. A and D both are inert elements.
f. C is the most abundant element in the Earth crust.

Question. Examine elements of the third period: Na, Mg, Al, Si, P, S, Cl and Ar Answer the following:
a. Choose (i) Metals, (ii) Non-metals out of these elements.
b. On which side of periodic table we find (i) metals (ii) non-metals.
c. Name metalloids out of the elements given above. 

Where are they located in the periodic table?
Answer : 
a. (i) Na, Mg, A1 are metals.
(ii) P, S, Cl, Ar are non-metals.
b. (i) Metals are placed on the left hand side and middle part of the periodic table.
(ii) Non-metals are placed on the right hand side of periodic table.
c. Silicon is a metalloid. They are located between metals and non-metals at the border line in a zigzag manner.