Please refer to Periodic Classification of Elements Class 10 Science Important Questions given below. These solved questions for Periodic Classification of Elements have been prepared based on the latest CBSE, NCERT and KVS syllabus and books issued for the current academic year. We have provided important examination questions for Class 10 Science all chapters.
Class 10 Science Periodic Classification of Elements Important Questions
Very Short Answer Type Questions :
Question. What would be the nature of oxides formed by the elements on the right side of periodic table?
Answer : On right hand side of the periodic table, most of them are non-metals, therefore they form acidic oxides.
Question. Predict the maximum number of valence electrons possible for atoms in the first period of the periodic table.
Answer : Maximum number of valence electrons in 1st period is 2.
Question. The electronic configuration of two elements X and Y are 2, 8, 7 and 2, 8, 8, 3 respectively. Write the atomic numbers of X and Y.
Answer :
X = 2 + 8 + 7 = 17
Y = 2 + 8 + 8 + 3 = 21
Question. The atomic numbers of three elements X, Y and Z are 3, 11 and 17 respectively. State giving reason which two elements will show similar properties.
Answer :
X= 2, 1
Y = 2,8, 1; Z = 2, 8, 7
X and Y will show similar properties due to same number of valence electrons.
Question. Give reason why noble gases are placed in a separate group in the modern periodic table.
Answer : It is because they have their outermost shell completely filled and resemble with each other.
Question. Name any two pairs of elements which were adjusted by Newlands in the same slot.
Answer : (i) Co and Ni, (ii) Ce and La
Question. Define Newlands law of octaves.
Answer : Newlands Law of Octaves: When elements are arranged in increasing order of their atomic mass, every eighth element resembles with the first.
Question. State Mendeleev’s periodic law.
Answer : Mendeleev’s Periodic Law: Properties of elements are a periodic function of their atomic mass.
Question. Name any two elements which were discovered later after the formation of Mendeleev’s periodic table.
Answer : Gallium and Germanium.
Question. What is a metalloid? Name any two of them.
Answer : Metalloids are those elements which resembles both with metals as well as non-metals e.g., Boron and Silicon.
Question. What is the valency of an element with atomic number 35?
Answer : Atomic number is 35, it has electronic configuration of 2, 8, 18, 7. It has 7 valence electrons, therefore its valency is equal to 1.
Question. What were the criteria used by Mendeleev in creating his periodic table?
Answer : Increasing order of atomic mass and same formula of oxides and hydrides.
Question. An element A has atomic number 16. To which group mand period does it belong to?
Answer : A(16) has electronic configuration: 2, 8, 6. It has 6 valence electrons and three shells. It belong to Group 16, 3rd period.
Question. Why are H, Li, Na and K placed in group-1?
Answer : It is because they have one valence electron.
Question. Write the number of horizontal rows in the modern periodic table. What are these rows called?
Answer : There are 7 horizontal rows in the modern periodic Table. These rows are called periods.
Question. Give the number of elements in 2nd and 5th period in the modern periodic table.
Answer :
In 2nd period, there are 8 elements.
In 5th period, there are 18 elements.
Question. What is the valency of phosphorus with atomic number 15?
Answer : P(2, 8, 5) has 5 valence electrons, therefore its valency is equal to 3.
Question. Which has larger atomic radius, K(19) or Ca(20)?
Answer : K has larger atomic radius than Ca.
Question. The formula of magnesium oxide is MgO. State the formula of barium nitrate and barium sulphate, if barium belongs to same group as magnesium.
Answer : The valency of Mg is 2. The valency of Ba is also 2 as they belong to the same group. Formula of Barium nitrate is Ba(NO3)2, and that of Barium sulphate is BaSO4.
Question. Write one difference between Group 1 and Group 2 elements?
Answer : Group 1 elements has 1 valence electron whereas group 2 elements has 2 valence electrons.
Question. Chlorine, Bromine and Iodine form Dobereiner’s triads. The atomic mass of Cl and I are 35.5 and 126.9 respectively. Predict the atomic mass of Bromine.
Answer: Atomic Mass of Br
= Atomic mass of Cl + Atomic mass of I/2
= 35.5 + 126.9 = 162 4/2 = 81.2
Electronic configuration: X = 2,8,7
It has 7 valence electrons. It belongs to group 17.
It has 3 shells, therefore it belongs to 3rd period.
It can gain 1 electron to become stable, so its valency is equal to 1.
Question. Write the trend of atomic size and metallic character along a group and a period in modern periodic table.
Answer: Atomic size increases down the group and decreases along a period from left to right in the periodic table.
Metallic character increases down the group and it decreases along a period from left to right.
Question. What would be the nature of oxides formed by the elements on the right side of periodic table?
Answer: On right hand side of the periodic table, most of them are non-metals, therefore they form acidic oxides.
Question. Define Newlands law of octaves.
Answer: Newlands Law of Octaves: When elements are arranged in increasing order of their atomic mass, every eighth element resembles with the first.
Question. The electronic configuration of two elements X and Y are 2, 8, 7 and 2, 8, 8, 3 respectively. Write the atomic numbers of X and Y.
Answer:
X = 2 + 8 + 7 = 17
Y = 2 + 8 + 8 + 3 = 21
Question. Elements in Periodic table show periodicity in properties. List any four such properties.
Answer: Valence electrons, Valency, Atomic size, Metallic character.
Question. How does metallic character of the elements change along a period in the periodic table from left to right and why?
Answer: Metallic character of elements decreases along a period from left to right because atomic size decreases, tendency to lose electrons decreases.
Question. Arrange the following metals in decreasing order of their atomic size:
Ca, Mg, Ba, Be
Answer: Ba > Ca > Mg > Be is the decreasing order of atomic size.
Question. Find the atomic number of the element whose electronic configuration is 2, 8, 5.
Answer: Atomic number = 2 + 8 + 5 = 15.
Question. The formula of magnesium oxide is MgO. State the formula of barium nitrate and barium sulphate, if barium belongs to same group as magnesium.
Answer: The valency of Mg is 2. The valency of Ba is also 2 as they belong to the same group. Formula of Barium nitrate is Ba(NO3)2, and that of Barium sulphate is BaSO4.
Question. Which has larger atomic radius, K(19) or Ca(20)?
Answer: K has larger atomic radius than Ca.
Question. Write the formula which is used to determine the maximum number of electrons that a shell can accommodate.
Answer: 2n2, where n is the shell number.
Question. Arrange the following elements in increasing order of their atomic radii:
a. Li, Be, F, N
b. Cl, At, Br, I
Ans :
a. F < N < Be < Li
b. Cl < Br < I < At
Question. How many vertical columns are there in the modern periodic table and what are they called?
Answer: There are 18 vertical columns in Modern Periodic Table. They are called groups.
Question. What is the valency of phosphorus with atomic number 15?
Answer: P(2, 8, 5) has 5 valence electrons, therefore its valency is equal to 3.
Question. What is the valency of an element with atomic number 35?
Answer: Atomic number is 35, it has electronic configuration of 2, 8, 18, 7. It has 7 valence electrons, therefore its valency is equal to 1.
Short Answer Type Questions :
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 non-metal.
(b) Atom of element C has a larger size ‘ than atom of element A.
(c) Element B has a valency of 1.
Answer. (a) It is because it has 7 valence electrons.
It can gain one electron to form negative ion. So, it is a non-metal.
(b)’C’ has more number of shells than A. So, it is larger in size.
(c)’B’ has one valence electron. It can lose one electron to become stable. So, 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. Atomic mass as a physical property and nature and formulae of oxide and hydride formed, and chemical property was used by Mendeleev.
Following are the two observations which posed a challenge to Mendeleev’s Periodic Law.
(i) Increasing order of atomic weights could not be maintained while matching chemical properties. Chemical properties do not depend upon atomic mass.
(ii) Isotopes have different atomic mass but same chemical properties.
Question. What were the limitations of Newlands’ Law of Octaves ?
Answer. Limitations:
(i) It was found that law of octaves was applicable only upto calcium because after Ca, every eighth element did not possess properties similar to first.
(ii) New elements discovered could not fit into the law of octaves on the basis of their properties.
(iii) Newland adjusted two elements in same slot e.g., Co and Ni which differ entirely from halogens. Iron resembles with Co and Ni, has been placed far away from these elements.
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 non-metal because it can gain electron easily as it has 7 valence electrons and forms negative ion with stable electronic configuration.
(b) It is because ‘B’ has lesser atomic number, less nuclear charge, less force of attraction between valence electrons and nucleus therefore, has larger atomic size.
(c) ‘C’ has 7 valence electrons. It can gain one electron to become stable. So, its valency is equal to one.
Question. Table given below shows a part of the Periodic Table.
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) They can lose electrons easily due to bigger size; energy required to remove electron is less.
(b) It is because of greater effective nuclear charge on Mg, i.e. more number of protons attract more number of electrons than Na.
(c) ‘F’ can form F– more easily than Cl due to smaller atomic size. F– is more stable than Cl–.
Therefore, fluorine is more reactive than chlorine.
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 same properties after definite interval is called periodicity in properties.
(b) It is because they have same valence electrons therefore, have similar properties.
(c) Tendency to gain electrons increases from left to right in a period because atomic size goes on decreasing and effective nuclear charge increases.
Question. (a) Why do we classify elements?
(b) What were the two criteria used by Mendeleev in creating his Periodic Table?
(c) Why did Mendeleev leave some gaps in his Periodic Table?
(d) In Mendeleev’s Periodic Table, why was there no mention of Noble gases like Helium, Neon and Argon?
(e) Would you place the two isotopes ‘ of chlorine, CI-35 and CI-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.
Answer. (a) It is done so as to study the properties of elements conveniently.
(b) Increasing order of atomic mass and similarities in chemical properties (especially nature and formulae of oxide and hydride formed).
(c) These gaps were left for undiscovered elements.
(d) Noble gases were not invented at that time.
(e) They will be kept at same slot as they have same chemical properties.
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 Modern Periodic Table with the atomic numbers of the elements in parenthesis.
(a) What is the electronic configuration of F?
(b) What is the number of valence electrons in the atom of F?
(c) What is the number of shells in the atom of F?
(d) Write the size of the atoms of E, F, G and H in decreasing order,
(e) State whether F is a metal or a non-metal.
(f) Out of the three elements B, E and F, which one has the biggest atomic size?
Answer.
(a) F has electronic configuration 2, 8, 2.
(b) F has 2 valence electrons.
(c) There are three shells in ‘F’.
(d) H > G > F > E is decreasing order of size of atoms.
(e) ‘F’ is a metal.
(f) ‘B’ is having biggest atomic size among B, E and F.
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:
(a) Which of these halogen ?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
(i) F is a halogen
(b) BF will be the formula of the compound formed
(c) C has atomic number 12 and electronic configuration is K = 2, L = 8, M = 2
E has atomic number 8 and electronic configuration is K = 2, L = 6
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 combine with chlorine to form an acid and common salt respectively. The oxide of element A is liquid at room temperature and is a neutral substance, while the oxides of the remaining six elements are basic in nature. Based on the above information, answer the following questions: What could the element A be?
(i) Will elements A to G belong to the same period or same group of the periodic table?
(iii) Write the formula of the compound formed by the reaction of the element A with oxygen,
(iv) Show the formation of the compound by a combination of element C with chlorine with the help of electronic structure.
(v) What would be the ratio of number of combining atoms in a compound formed by the combination of element A with carbon?
(vi)Which one of the given elements is likely to have the smallest atomic radius?
Answer. (i)’A’ is hydrogen because its oxide H2O is liquid at room temperature .
(ii)A to G belong to same group of the periodic table as these have same number of valence electrons.
Question. (a) What are ‘groups’ and ‘periods’ in the ‘periodic table’?
(b) Two elements M and N belong to group I and II respectively and are in the same period of the periodic table. How do the following properties of M and N vary?
(i) Sizes of their atoms
(ii) Their metallic characters
(iii) Their valencies in forming oxides
(iv) Molecular formulae of their chlorides
Answer. (a) The vertical columns in the periodic table are called ‘groups’. The horizontal rows in the periodic table are called ‘periods’.
(b) (i) ‘M’ and ‘N’ belong to same period but group I and II. Therefore, ‘N’ will be smaller than ‘M’ as atomic size goes on decreasing from left to right.
(ii) ‘M’ is more metallic than ‘N’. Metallic character goes on decreasing from left to right as tendency to lose electrons decreases due to decrease in atomic size.
(iii) Their valencies are 1 and 2 respectively in forming oxides. Valency goes on increasing first and then decreases.
(iv) MCI, NCI2 are molecular formulae of their chlorides.
Question. The atomic number of three elements are given below:
A(5), B(7), C(10)
Write the symbol of element which belongs to (a) group 13, (b) group 15 of the periodic table. State the period of periodic table to which these elements belong to. Give reason to your answer.
Answer: a. A(5): 2, 3 belong to group 13 because it has 3 valence electrons.
b. B(7): 2, 5 belong to group 15 because it has 5 valence electrons.
They i.e., A and B belong to second period because they have 2 shells.
Question. Two elements X and Y belong to group 1 and 2 respectively in the same period of periodic table. Compare them with respect to: periodic table from the left to the right and why?
(a) the number of valence electrons in their atoms
(b) their valencies
(c) metallic character
(d) the sizes of their atom
(e) formulae of their oxides formulae of their chlorides
Answer. (a) ‘X’ has 1 valence electron, Y has 2 valence electrons.
(b) ‘X’ has valency equal to 1, V has valency equal to 2.
(c) ‘X’ is more metallic than Y.
(d) ‘X’ is bigger than Y.
(e) X20 and YO are formulae of their oxides.
(f) and YCI2 are formulae of their chlorides.
Question. Choose from the following: 4Be, 9F, 19K, 20Ca
a. The element having one electron in the outermost shell.
b. Two elements of the same group.
Answer:
a. 19K(2,8,8,1) has one valence electron,
b. 4Be(2, 2) and 20Ca(2, 8, 8, 2) belongs to the same group.
Question. Out of the elements H(1), Be(4), Na(11) and Mg(12).
a. Write the pair of elements having similar chemical properties.
b. State the group number of each pair,
c. Name one another element belonging to each of these groups.
Answer:
a. Be(4) and Mg(12) have similar chemical properties.
H( 1) and Na(ll) have similar chemical properties.
b. Be and Mg belong to group 2, H and Na belong to group 1.
c. K belongs to group 1 and Ca belongs to group 2.
Question. The elements of the second period of the periodic table are given below:
Li, Be, B, C, N, O, F
a. Give reason to explain why atomic radii decreases from Li to F.
b. Identify the most (i) metallic and (ii) non-metallic element.
Answer:
a. It is because effective nuclear increases due to increase in forces of attraction between more electrons with more protons, even though number of shells remain the same.
b. (i) Li is the most metallic element, (ii) F is the most non-metallic element.
Question. Li, Be, B, C are the elements of same period of Modem Periodic table.
a. Arrange them in increasing order of their atomic size.
b. In which shell (number) would last electron enter for all of them.
c. Calculate the valence electrons in each.
d. Which element amongst them is most electropositive?
Answer:
a. C < B < Be < Li
b. Second shell 93
They have 1, 2, 3, 4 valence electrons respectively.
d. Li is the most electropositive element.
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 of X when it reacts with hydrogen and write its electron dot diagram.
c. Name the element X and state whether it is metallic or non-metallic.
Answer:
a. X has 6 valence electrons and its valency is equal to 2.
b. H2X is its formula,
c. X is sulphur. It is a non-metallic element.
Question. Name the element with atomic number 19.
a. In which group it is placed?
b. To which period does it belong to?
c. Write its electronic configuration.
Answer:
The name of element is Potassium, K(19): 2, 8, 8, 1.
a. It belongs to group 1.
b. It belongs to 4th period.
c. Its electronic configuration is 2,8 8,1.
Question. The atomic number of an element is 20.
a. Write its electronic configuration and determine its valency.
b. Is it a metal or a non-metal?
c. Write formula of its chloride.
d. Is it more or less reactive than Mg(12)? Give reasons for your answer.
Answer:
a. Ca(20): 2, 8 8, 2. Its valency is equal to 2.
b. It is a metal.
c. CaCl2.
d. It is more reactive than Mg due to larger atomic size. It can lose electrons easily due to less effective nuclear charge.
Question. What is periodicity in properties of elements with reference to the Modern Periodic Table? Why do all the elements of the same group have similar properties?
How does the tendency of elements to gain electrons change as we move from left in a period? State the reason of this change.
Answer: The repetition of similar properties after a definite interval is called periodicity of properties.
Tendency to gain electrons increases along a period from left to right because atomic size decreases.
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:
(a) Which of these halogen ?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:
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 Modern Periodic Table with the atomic numbers of the elements in parenthesis.
1. What is the electronic configuration of F?
2. What is the number of valence electrons in the atom of F?
3. What is the number of shells in the atom of F?
4. Write the size of the atoms of E, F, G and H in decreasing order,
5. State whether F is a metal or a non-metal.
6. Out of the three elements B, E and F, which one has the biggest atomic size?
Answer:
1. F has electronic configuration 2, 8, 2.
2. F has 2 valence electrons.
3. There are three shells in ‘F’.
4. H > G > F > E is decreasing order of size of atbms.
5. ‘F’ is a metal.
6. ‘B’ is having biggest atomic size among B, E and F.
Question. F, Cl and Br are the elements each having seven valence electrons. Which of these (a) has the largest atomic radius, (b) is most reactive? Justify your answer stating reason for each.
Answer:
(a) Bromine has largest atomic radius because it has four shells: 2, 8, 18, 7.
(b) Fluorine is most reactive because it is smallest in size and can gain electron easily.
Question. Na, Mg and Al are the elements having one, two and three valence electrons respectively. Which of these elements (a) has the largest atomic radius, (b) is least reactive? Justify your answer stating reason for each.
Answer: (a) Na has the largest atomic radius because it has 11 protons and 11 electrons, therefore least effective nuclear charge.
(b) Al is least reactive because it has smallest atomic size due to 13 protons and 13 electrons, it has greater effective nuclear charge, therefore, cannot lose electrons easily, hence it is least reactive.
Question. The atomic numbers of three elements are given below:
Write the symbol of the element which belongs to (a) group 1, (b) group 14, of the periodic table. State the period of the periodic table to which these elements belong. State reason to support your answer.
Answer:
(a) A belongs to group 1.
(b) B belongs to group 14.
These elements belong to second period because these elements have two shells. A has electronic configuration 2, 1 and has one valence electron so, belongs to group 1. ‘B’ has electronic configuration 2, 4 and has four valence electrons so, belongs to group 14 and period 2. ‘C’ has electronic configuration 2, 7 and has one valence electron. All of them contain two shells and so belong to second period.
Question. (a) How many periods are there in the Modern Periodic Table of elements?
(b) How do atomic radius, valency and metallic character vary down a group?
(c) How do the atomic size and
metallic character of elements vary as we move from left to right in a period?
Answer:
(a) There are 7 periods.
(b) Atomic radius goes on increasing down the group, valency remains same. Metallic character increases down the group.
(c) Atomic size decreases along a period from left to right. Metallic character decreases along a period from left to right.
Question. Choose from the following:
4Be,9F,19K,20Ca
(a) The element having one electron in the outermost shell.
(b) Two elements of the same group.
Answer:
(a) 19K has one valence electron.
(b) 4Beand 20Cabelong to the same group.
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 combine with chlorine to form an acid and common salt respectively. The oxide of element A is liquid at room temperature and is a neutral substance, while the oxides of the remaining six elements are basic in nature. Based on the above information, answer the following questions: What could the element A be?
(i) Will elements A to G belong to the same period or same group of the periodic table?
(iii) Write the formula of the compound formed by the reaction of the element A with oxygen,
(iv)Show the formation of the compound by a combination of element C with chlorine with the help of electronic structure.
(v) What would be the ratio of number of combining atoms in a compound formed by the combination of element A with carbon?
(vi)Which one of the given elements is likely to have the smallest atomic radius?
Answer:
(i)’A’ is hydrogen because its oxide H2O is liquid at room temperature .
(ii) A to G belong to same group of the periodic table as these have same number of valence electrons. img
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 non-metal because it can gain electron easily as it has 7 valence electrons and forms negative ion with stable electronic configuration.
(b) It is because ‘B’ has lesser atomic number, less nuclear charge, less force of attraction between valence electrons and nucleus therefore, has larger atomic size.
(c) ‘C’ has 7 valence electrons. It can gain one electron to become stable. So, its valency is equal to one.
Question. (a) How are the following related?
1. Number of valence electrons of different elements in the same group.
2. Number of shells of elements in the same period.
(b) How do the following change?
1. Number of shells of elements as we go down a group.
2. Number of valence electrons of elements on moving from , left to right in a period.
3. Atomic radius in moving from left to right along a period.
4. Atomic size down a group.
Answer:
(a)
1. Different elements in same group have same number of valence electrons.
2. Number of shells of elements in same period are equal.
(b)
1. Number of shells of elements goes on increasing down the group.
2. Number of valence electrons of elements goes on increasing on moving from left to right in a period, e.g. lithium has 1, beryllium has 2, boron has 3, carbon has 4, nitrogen has 5, oxygen has 6, fluorine has 7 and neon has 8 valence electrons.
3. Atomic radius goes on decreasing in moving from left to right along a period.
4. Atomic size goes on increasing down a group.
Question. The atomic number of an element is 19.
a. Write the electronic configuration of this element and determine (i) the valency of this element, and (ii) whether this element is a metal or a nonmetal?
b. Write the formula of the oxide of this element.
c. Is this element more reactive or less reactive than Na (atomic number 11)? Justify your answer, giving example.
Answer:
a. 2, 8, 8, 1
i. Valency = 1
ii. It is a metal.
a. X2O
b. It is more reactive than Na(11) because it is large in size and it can lose electrons easily due to less effective nuclear charge.
K reacts more vigorously with H2O than Na.
Question. Why is atomic number considered to be a more appropriate parameter than atomic mass for the classification of elements in a periodic table? How does the metallic character of elements vary as we move (a) from left to right in a period, and (b) top to bottom in a group of the modem periodic table?
Answer: It is because chemical properties depend upon the number of valence electrons which is determined with the help of atomic number.
a. Metallic character decreases from left to right because atomic size decreases, tendency to lose electrons decreases,
b. Metallic character increases from top to bottom in a group because atomic size increases due to which effective nuclear charge decreases.
Question. a. Identify the elements among the following which will belong to the same group: H, He, Li, B, C.
b. State the group number of the recognised elements.
c. Name another one element belonging to the same group.
Answer:
a. H and Li belong to the same group.
b. They belong to group 1.
c. Na (sodium) also belong to this group.
Question. Justify the following with suitable reasons:
a. Cations are smaller than the corresponding atoms.
b. Size of atom increases as we move down the group.
c. Atomic size decreases as we move across a period.
Answer:
a. Cations are formed by loss of electrons, therefore effective nuclear charge increases, size of atom decreases.
b. It is because number of shells goes on increasing down the group.
c. It is because effective nuclear charge increases along a period.
Question. State Mendeleev’s periodic law. Write two achievements of Mendeleev’s periodic table.
Answer: Properties of elements are a periodic function of their atomic mass.
Achievements:
a. It could arrange all the elements discovered at that time.
b. It left some gaps for the elements to be discovered and helped in their discovery by predicting their properties.
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.
Questiona. Which atom is bigger, Na or Mg? Why?
b. Identify the most (i) metallic and (ii) non-metallic element in Period 3.
Answer:
a. Na is bigger because it has 11p and 11e i.e., less forces of attraction than in Mg which has 12 protons and 12 electrons and has more forces of attraction, due to more effective nuclear charge.
b. (i) Na is the most metallic element, (ii) Cl is the most non-metallic element.
Question. An element X’(Atomic number 20) burns in the presence of oxygen to form a basic oxide.
a. Identify the element and write its electronic configuration.
b. State its group number and period number in the Modern Periodic Table.
c. Write a balanced chemical equation for the reaction when this oxide is dissolved in water.
Answer:
a. X is calcium because it forms CaO (basic oxide). Its electronic configuration is 2, 8 8, 2.
b. It belongs to group 2 and 4th period.
c. CaO + H2O → Ca(OH)2
Question. How does valency of the elements vary
a. in going down a group, and
b. in going from left to right in a period of the periodic table?
Answer:
a. It remains the same.
b. It first increases till middle, then decreases.
Question. Calcium is an element with atomic number 20.
a. Will it be a metal/non-metal?
b. What will be its valency?
c. What would be the formula of its chloride?
d. Will it be smaller / larger than K?
Answer:
Ca(20): 2, 8, 8, 2
a. It will be a metal.
b. Its valency is equal to 2.
c. CaCl2 is the formula of its chloride.
d. It will be smaller than K.
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?
Ans : 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. The electrons in the atoms of four elements A, B, C and D are distributed in three shells havingl, 3, 5 and 7 electrons in the outermost shell respectively. State the period in which these elements can be placed in the modern periodic table. Write the electronic configuration of the atoms of A and D and the molecular formula of the compound formed when A and D combine.
Answer:
A: 2, 8, 1
B: 2, 8, 3
C: 2, 8, 5
D: 2, 8, 7
They belong to the 3rd period.
AD is the molecular formula.
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:
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. Explain the basic character of oxides of elements down the group and across the period.
Answer: Basic character of oxides increases down the group because metallic character increases.
Basic character of oxides decreases along the period from left to right because non¬metallic character increases, metallic character decreases.
Question. An element has atomic number 13.
a. What is the group and period number to which this element belongs to?
b. Is the element a metal or a non-metal?
Answer:
a. It belongs to group 13, 3rd period because it has 3 valence electrons and 3 shells.
b. It is a metal because it can lose 3 electrons to become stable.
Question. Study the variation in atomic radii of first group elements given below and arrange them in an increasing order:
a. Name the element which have the smallest and the largest atoms
b. How does the atomic size vary as you go down the group?
Answer:
Li < Na < K < Rb < Cs
a. Li is the smallest, Cs is the largest atom.
b. Atomic size increases down the group.
Question. a. How many periods are there in the Modem Periodic Table of elements?
b. How do atomic radius, valency and metallic character vary down a group?
c. How do atomic size and metallic character of elements vary as we move from left to right in a period?
Answer:
a. There are 7 periods.
b. Atomic radius and Metallic character increases down the group. Valency remains the same in a group.
c. Atomic size and metallic character decrease along a period from left to right in a period.
Question. Explain the variation in the following properties of the elements in periodic table:
a. Atomic radius in the periodic table,
b. Metallic character in a period,
c. Valency in a group.
Answer:
a. Atomic radius and Metallic character increases down the group. Valency remains the same in a group.
b. Atomic size and metallic character decrease along a period from left to right in a period.
Question. The elements of group 18 of the periodic table are given:
He, Ne, Ar, Kr, Xe, Rd, Dg
a. The elements of this group are unreactive, why?
b. Which atom is bigger in size Ne or Ar and why?
Answer:
a. It is because they have their octet complete i.e., stable electronic configuration.
b. Ar has bigger atomic size than Ne because Ar has 3 shells while Ne has 2 shells; Ar (2, 8, 8), Ne (2, 8)
Question. Given below are some elements of the modern periodic table:
4Be, 9F, 14Si, 19K, 20Ca
a. Select the element that has one electron in the outermost shell and write its electronic configuration.
b. Select two elements that belong to the same group. Give reason for your answer.
c. Select two elements that belong to the same period. Which one of these two has bigger atomic size?
Answer:
a. 19K: 2, 8, 8, 1
b. 4Be, 20Ca belong to the same group because both have same number of valence electrons.
Be: 2, 2; Ca: 2, 8, 8, 2
c. 4Be, 9F belong to the same period. 4Be has bigger atomic size than 9F.
Question. a. Predict which of the following will form anions and which will form cations.
(i) Na, (ii) Al, (iii) Cl, (iv) O
b Name two elements that are inert.
Answer:
a. Cl and O will form anions i.e., Cl- and O2- Na and A1 will form cations i.e., Na+ and Al3 +.
b. He and Ne are inert elements.
Question. a. How does electropositivity of elements gets affected as we move (i) down the group, (ii) across the period?
b. Which atomic property increases both ways: as we move across the period or down the group?
Answer:
a. (i) Electropositivity increases down the group.
(ii) Electropositivity decreases across the period from left to right.
b. Atomic number increases across the period as well as down the group.
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. 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. C is sodium.
Na → Na+ + e- or C → C+ + e-
Cl + e- → Cl- or Cl + e-→Cl
e. CA4 i.e., 1:4
f. A has smallest atomic radius.
Question. Based on the group valency of elements state the formula for the following giving justification for each:
a. Oxides of 1st group elements,
b. Halides of the elements of group 13, and c. Compounds formed when an element of group 2 combines with an element of group 16.
Answer:
a. M2O
b. MCl3
c. CaO
Question. How many groups and periods are there in the Modern Periodic Table? How do the atomic size and metallic character of elements vary as we move
a. down a group and b. from left to right in a period?
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. a. Define the following terms (i) Valency, (ii) Atomic size
b. How do the valency and the atomic size of the elements vary while going from left to right along a period in the modern periodic table?
Answer:
a. (i) Valency: It is the number of electrons lost or gained or shared by an atom.
(ii) Atomic size: It is the distance between centre of the nucleus and outermost shell of an atom.
b. Valency first increases till middle and then decreases. Atomic size decreases from left to right along a period.
Question. The elements Li, Na and K each having one valence electron, are in period 2, 3 and 4 respectively of modern periodic table.
a. In which group of the periodic table should they be placed?
b. Which one of them is least reactive?
c. Which one of them has the largest atomic radius?
d. Give reason to justify your answer in each case.
Answer:
a. They belong to group 1 because they have one only valence electron.
b. Lithium (Li) is the least reactive because it is smallest in size, has least tendency to lose electrons.
c. K has largest atomic radius because it has maximum number of shells.
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.
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 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.
b. Valency is 2.
c. Ca is the most reactive metal.
Question. In the figure given below the first 20 elements are jumbled up. Carefully observe the figure and answer the following questions:
a. Pick out the two elements which are known as alkali metals.
b. Pick out the two elements which have valency of 4.
c. Pick out two elements which belong to group 16 of the periodic table.
Answer:
a. Na, K are alkali metals.
b. C, Si have valency equal to 4
c. O and S belongs to group 16.
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.
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. The atomic number of Na and Mg are 11 and 12 respectively and they belong to the same period a. Which one should have smaller atomic size?
b. Which would be more electropositive?
c. To which group would each one belong?
Answer:
Na(11): 2, 8, 1; Mg(12): 2, 8, 2
a. Mg will have smaller size.
b. Na is more electropositive.
c. Na(11) belongs to group 1 whereas Mg(12) belongs to group 2.
Question. In the following table, the position of six elements A, B, C, D, E and F are given 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. Name the element which is a metal with valency of three.
c. Name the element which is a non-metal with valency of three.
d. Out of B and C, whose atomic radius is bigger and why?
e. Write the common name of the family to which the elements D and F belongs to?
Answer:
a. E is an element which form covalent compounds.
b. B is a metal with a valency of 3.
c. C is a non-metal with a valency of 3.
d. B has bigger size.
e. D and F belong to Noble gases.
Question. What is meant by ‘group’ in the modern periodic table? How do the following change on moving from top to bottom in a group?
a. Number of valence electrons.
b. Number of occupied shells.
c. Size of atoms.
d. Metallic character of elements.
e. Effective nuclear charge experienced by valence electrons.
Answer:
The vertical column of the periodic table is called group.
a. Number of valence electrons remains the same in a group.
b. Number of occupied shells goes on increasing down a group.
c. Size of atom increases down the group.
d. Metallic character of element increases down the group.
e. Effective nuclear charge decreases down the group.
Question. Lithium, Sodium, Potassium are placed in the same group on the basis of their similar properties. List three such similar properties.
Answer:
a. All of them are reactive metals.
b. They have 1 valence electron and form positive ions with +1 charge.
c. They are largest in size in their respective periods.
