Maharashtra Borad Solutions for Class 10 Science part-1 Chapter 2 Periodic Classification Of Elements

 Q.1. Textbook activity question   

1] Write the molecular formulae of oxides of the following elements by referring to the Mendeleev’s periodic Na, Si, Ca, C, Rb, P, Ba, Cl, Sn, Ca

Element Molecular formula Element Molecular formula
Na Na2O P P2O5
Si SiO2 Ba BaO
Ca CaO Cl Cl2O7
C CO2 Sn SnO2
Rb Rb2O  

 

 

  • Q. 2 . There are some vacant places in the Mendeleev’s periodic table. In some of these places the atomic masses are seen to be Enlist three of these predicted atomic masses along with their group and period.                                                Ans Three of these predicted atomic masses along with their group and period are:
  1. atomic mass = 44, group III and period 4
  2. Atomic mass = 68, group III and period 5
  3. Atomic mass = 72, group IV and period 5                                                                                                                                                 Q.3. What is the difference between the molecules of elements and compounds?                                                             Ans Molecules of elements contain atoms of the same element where as molecules of compounds contain atoms of two or more different elements.     
  4. Q.4. Arrange the above elements vertically downwards in an increasing order of atomic
Element K Na Rb Cs Li
Atomic radius (pm) 231 186 244 262 151

Ans: 

Element  Li Na K Rb Cs

5 .Which similarity do you find in their configuration?
Ans From the above electronic configurations, we can say that the number of valence electrons of all the elements
is the same which is 1.

6. Chlorine has two isotopes,viz, C1-35 and C1- 37. Their atomic masses are 35 and 37 respectively. Their chemical properties are same. Where should these be placed in Mendeleev’s periodic table? In different places or in the same place?
Ans:  Mendeleev arranged the elements in increasing order of atomic mass. Since the atomic masses of the
isotopes of chlorine are 35 and 37, they should be kept in different positions in the Mendeleev Periodic table.

7 How did the position of and get fixed in the modern periodic table?
Ans:  (i) Modem Periodic table is based on atomic numbers, So, the position of isotopes of elements was decided by arranging the elements in the ascending order of their atomic numbers.
(ii) As isotopes have the same atomic number they do not need to be given different positions (slots).

8 What are the types of elements?
Ans: metals, metalloids, and nonmetals

9 How many valence electrons are there in each of these elements?
Ans Number of valence electrons in each of the these elements is 1.

10 Go through the modern periodic table and write the names one below the other of the elements of group 1.
Ans The modern periodic table is given below:
Four elements of group 1 :Hydrogen (H)
                                          Lithium (Li)
                                         Sodium (Na)
                                         Potassium (K)

11. By referring to the modern periodic table find out the periods to which the above elements belong.

Element K Na Rb Cs Li
Atomic radius (pm) 231 186 244 262 152

Ans  All the given elements belong to group 1 of the modern periodic table.

12. Is the number of shells the same in these?
Ans Number of Shells is same in these elements i.e.2.

13. What is the expected trend in the variation of nonmetallic character of elements from left to right in a period?
Ans  Non-metallic character increases from left to right in a period.

14. What are the types of matter?
Ans i. Solids – relatively rigid, definite volume and shape. In a solid, the atoms and molecules are attached to
each other. …
ii. Liquids – definite volume but able to change shape by flowing. In a liquid, the atoms and molecules are
loosely bonded. …
iii. Gases – no definite volume or shape.

15. How is the problem regarding the position of cobalt ( Co) and nickel ( Ni) in Mendeleev’s periodic table resolved in modern periodic table?
Ans (i) According to Mendeleev.s periodic law, elements are arranged in the order of their increasing atomic masses.
(ii) When Co. and Ni were put in the group on the basis of their chemical properties it was found that Co having higher mass of 58.9 comes first and Nickel with slightly lower atomic mass of 58.7 comes later.
(iii) Modem Periodic table resolved this problem. According to the Modem Periodic law, elements are arranged in their increasing order of atomic number.
(iv) The atomic number of Cobalt is 27 comes first and Nickel with atomic number 28 comes next even if their atomic masses are in the reverse order.

16. Look at the elements of the third period. Classify them into metals and nonmetals.
Ans The third period contains eight elements: sodium (Na), magnesium (Mg), aluminium (Al), silicon (Si), phosphorus (P), sulfur (S), chlorine (Cl), and argon (Ar). Metals – (sodium, magnesium, aluminium), Nonmetals – (phosphorous, sulfur, chlorine, argon) and one is metalloid (silicon).

17. On which side of the period did you find the nonmetals?
Ans On the right side of the periodic table, we find non-metals.

18. Can there be an element with atomic mass 53 or 54 in between the two elements, chromium  2453Cr and manganese  55 25Mn ?
Ans :  It is not possible. Since their atomic numbers are continuous, there cannot be an element between Chromium and Manganese.

19. Does this arrangement match with the pattern of the group 1 of the modern periodic table?

Element

K

Na Rb Cs Li
Atomic radius (pm) 231 186 244 262

151

  Ans:  Yes. The arrangement of the elements as per the increasing order of atomic radius matches with group 1 of the modern periodic table. 20 What do you think? Should hydrogen be placed in group.

20. of halogens or group 1 of alkali metals in the modern periodic table?
Ans : (i) Hydrogen fits in its current position in the periodic table (group 1) much better than in group 17 (though is not a perfect position). For example Hydrogen forms oxide (H O) just like oxides of alkali metals (Na O,
K O). It has the same common charge ( + 1) as all alkali metals.
(ii) It resembles halogens in forming diatomic molecules
H , Cl , F , Br .
(iii) It does not behave like halogens, being mainly in the + 1 oxidation state. It does not happen to be like
halogens, the most stable compounds of halogens have either -1 or a very high oxidation state like -7 or +5.)
(iv) Hydrogen has one electron in the outermost shell and it is placed in top of group/based on atomic number.

21. On which side of the period are the metals? Left or right?
Ans:  Left side of the period is the metals.

22. Does this arrangement match with the pattern of the second period of the modern periodic table?

Element O B C N Be Li
Atomic radius (pm) 66 88 77 74 111 152

Ans:  Yes. The arrangement of the elements matches with the second period of the modern periodic table because the elements were aranged in the decreasing order of their atomic radius.

23. On going through the modern periodic table it is seen that the elements Li, Be, B, C, N, O, F and Ne belong to period-2. Write down the electronic configuration of all of them.
Ans:  Electronic configuration of the elements :

Li Be B C N O F Ne
2, 1 2, 2 2, 3 2, 4 2, 5 2, 6 2, 7 2, 8

24. Write the electronic configuration of the first four elements in this group.
Ans:  Elements Electronic configuration

Elements Electronic configuration
Hydrogen 1
Lithium 2, 1
Sodium 2, 8, 1
Potassium 2, 8, 8, 1

25. Due to uncertainty in the names of some of the elements, a question mark is indicated before the symbol in Mendeleev’s periodic table. What are such symbols?
Ans:  Mendeleev arranged the elements in the increasing order of atomic masses. In some places the atomic mass of elements would not be in right order to put them in the correct group. Tellurium is heavier than Iodine, but he put Iodine after Tellurium because Iodine has similar properties like F, Cl, Br. He placed the elements according to their properties and put a question mark to indicate that the atomic mass needs to be checked. for e.g.? Yt = 88 in Mendeleev.s periodic table was corrected as Yt = 88.906 in Modem Periodic table.

26 What is the cause of nonmetallic character of elements?
Ans :  The tendency to form anion by accepting outside electrons into its valence shell or electronegativity is the cause of nonmetallic character of an element. 

27. What are the smallest particles of matter called?
Ans The smallest particles of matter are called atoms and molecules.

28 Is the number of valence electrons same for all these elements?
Ans The number of valence electrons is different for all these elements.

29. What would be the expected trend in the variation of nonmetallic character of elements down a group?
Ans:  The nonmetallic character decreases down a group.

30. Write the molecular formulae of the compounds of the following elements with hydrogen by referring to the
Mendeleev’s periodic table. C, S, Br, As, F, O, N, Cl
Ans:

Elements Compounds (with hydrogen)
C CH4 Methane
S H2S Hydrogen sulphide
Br HBr Hydrogen bromide
As AsH3 Arsine
F HF Hydrogen fluoride
O H2O Water
N NH3 Ammonia
Cl HCl Hydrogen chloride

Q.2 Multiple Choice Questions 

1. Which of the following is used on periodic table to represent name of elements
a. Number       b. Letter and number combination                     c. Symbols           d. Signs
Ans Option c.

2. Which is a property of the gases in group 18.
a. malleability.
b. brittleness.
c. high electrical conductivity.
d. unlikely to react with other elements.
Ans Option d.

3. Molecular formula of the chloride of an element X is XCl. This compound is a solid having high melting point. Which of the following elements be present in the same group as X.
a. Na               b. Mg        c. Al        d. SI
Ans Option a.

4 Which of the following is a Dobereiner’s triad.
a. Ne, Ca, Na         b. H , N , O          c. Li, Na, K        d. Na, Bx, Ax
Ans Option c.

5. Dobereiner’s Group Of Three Elements was known as …………… .
a. Octaves b. Duplets c. Triads d. None Of The Above
Ans Option c.

6. Alkaline earth metals have valency 2. This means that their position in the modern periodic table is in …..
a. Group 2      b. Group 16      c. Period 2        d. d-block
Ans Option a.

7 Which of the following statements about the modern periodic table is correct.
a. It has 18 horizontal rows known as periods
b. It has 7 vertical columns known as periods
c. It has 18 vertical columns known as groups
d. It has 7 horizontal rows known as groups
Ans Option c.

8 As we move across the period the number of electron shell
a. Increases b. Decreases c. Remains same d. All of the above
Ans Option c.

9 In which block of the modern periodic table are the nonmetals found?
a. s-block b. p-block c. d-block d. f-block
Ans Option b.

10 The law of triad is not applicable on
a. Cl, Br, I b. S, Se, Te c. Na, K, Rb d. Ca, Sr, Ba
Ans Option c.

11 He arranged the elements in increasing order of their atomic masses in a group of three ……………
a. Mosely b. Mendeleev c. Dobereiner d. Thompson
Ans Option c.

12 The position of which elements is still not clear (uncertain) in periodic table not even in modern periodic table
a. Sodium b. Magnesium c. Hydrogen d. Argon
Ans Option c.

13 Mendeleev’s periodic table was organized on the basis of following properties.
a. Only physical properties
b. Only chemical properties
c. Both physical and chemical properties
d. None of the above
Ans Option c.

14 In the Mendeleev’s periodic table gaps were left for the elements to be discovered later. Which of the following elements found in the periodic table.
a. Germanium b. Chlorine c. Oxygen d. Silicon
Ans Option a.

Q.3 Find the odd one out :
1. Nitrogen, Neon, Argon, Helium
Ans Nitrogen. (The others are inert gases.)

2. Newlands, Moseley, Dobereiner, Mendeleev
Ans Moseley (Moseley brought out the importance of atomic number, while the other tried to classify the elements on the basis of atomic mass.)

3. Sodium, Aluminium, Chlorine, Carbon
Ans Carbon (Carbon belongs to the second row, while the others belong to third row)

4. Temperature, Conduction, Convection, Radition
Ans Temperature (Others are modes of transfer of heat.)

5. Cal/g, cal/g°C, kcal/kg.°C, erg/g.°C
Ans Cal/g [(Others are units) of specific heat capacity.]

6. The joule, The erg, The calorie, The newton
Ans The newton [Others are units of energy (as well as work)]

7. Fluorine, Sulphur, Bromine, Iodine
Ans Sulphur (Others are halogens)

Q. 4. Find co-related terms :
1. Triads : …………… :: Octaves : Group of 8 elements
Ans Triads : Group of 3 elements :: Octaves : group of 8 elements

2. Dobereiner’s : Law of triad : : John Newland : ……………
Ans Dobereiner’s : Law of triad : : John Newland : Law of octaves

3.  Al : Al O : : P : ……………
Ans Al : Al O : : P : P O

4. Potassium : …………… : : Magnesium : Alkaline earth metal
Ans Potassium : Alkali metal : : Magnesium : Alkaline earth metal

5. No of period : Number of shells around nucleus :: Number of group number : …………….
Ans No of period : Number of shells around nucleus :: Number of group number : No of valence electron

6 Electro positivity : …………… :: Electro negativity : Non metallic character
Ans Electro positivity : Metallic character :: Electro negativity : Non metallic character

7. Metals : Cation :: Non metal : ……………
Ans Metals : Cation :: Non metal : Anion

8 .Sodium : Metal : : Chlorine : ……………
Ans Sodium : Metal : : Chlorine : Nonmetal

9. Oxygen : Valency 2 : : Nitrogen : ……………
Ans  Oxygen : Valency 2 : : Nitrogen : Valency 3

10. Molecular formula of beryllium oxide : BeO : : Molecular formula of beryllium chloride: ……………
Ans Molecular formula of beryllium oxide : BeO : : Molecular formula of beryllium chloride: BeCl

11. Eka-Boron : …………… : : Eka-Aluminium : Gallium (Ga)
Ans Eka-Boron : Scandium (Sc) : : Eka-Aluminium : Gallium (Ga)

Q.5 Match the pair:   

     1.

Column “A” Column “B”
i. Elements with atomic number 19 a. Group 18
ii. Element Q in period 3 which has the highest electron affinity b. Group 1
  c. Group 17
  d. Group 13

Ans:

i. Elements with atomic number 19 Group 1
ii. Element Q in period 3 which has the highest electron affinity Group 17

 

2.

  i. Triads Law a. 1866
  ii. Law Of Octaves b. 1859
  c. 1817
  d. 1807

Ans:

i. Triads Law 1817
ii. Law Of Octaves 1866

 

3]

Column “A” Column “B”
i. Dobereiner’s a. French Scientist
ii. John New Lands b. German Scientist
  c. Russian Scientist
 

d. English Scientist

Ans: 

i. Dobereiner’s German Scientist
ii. John New Lands English Scientist

4.

Column “A” Column “B”
i. Element which losses 3 electrons to form a cation a. Group 18
ii. Elements with atomic number 19 b. Group 13
  c. Group 16
  d. Group 1

Ans: 

i. Element which losses 3 electrons to form a cation Group 13
ii. Elements with atomic number 19 Group 1

5] 

Column “A” Column “B”
i. Elements with electronic configuration 2 a. Group 16
ii. Elements with valency ( – 2 ) b. Group 18
  c. Group 17
  d. Group 1

Ans: 

i. Elements with electronic configuration 2 Group 1
ii. Elements with valency ( – 2) Group 16

6] 

Column “A” Column “B”
i. Metals a. Amphoteric Oxides
ii. Non Metals b. Basic Oxides
  c. Acidic Oxides

 Ans:

i. Metals Basic Oxides
ii. Non Metals Acidic Oxides

 7]

Column “A” Column “B”
i. Electro negativity across the period a. Increases
ii. Non metallic character down the group b. Remains the same
  c. Decreases

 Ans:

i. Electro negativity across the period Increases
ii. Non metallic character down the group Decreases
Column “A” Column “B”
i. Eka- Boron a. Germanium
ii. Eka- Aluminium b. Silicon
  c. Scandium
  d. Gallium

 

 

8

i. Eka- Boron Scandium
ii. Eka- Aluminum Gallium

 

 

Ans

i. Eka- Borer Scandium
ii. Eka- Aluminum Gallium

Q.6 State True or False :

1. All the 118 elements are now discovered.
Ans All the 118 elements are now discovered – True

2. All the non metals lie on the right side of zig zag line drawn in p block.
Ans All the non metals lie on the right side of zig zag line drawn in p block – True

3 The number of shells in the elements of third period is three.
Ans The number of shells in the elements of third period is three – True

4 According to Dobereiner’s properties of elements are related to their atomic masses.
Ans According to Dobereiner’s properties of elements are related to their atomic masses – True

5 Periodic table has 18 periods and 7 groups.
Ans Periodic Table Has 18 Periods And 7 Groups – False
Periodic Table Has 7 Periods And 18 Groups

Q.7 Name the following :

1. The three metals in the third period of the modern periodic table.
Ans i. Sodium ii. Magnesium iii. Aluminium

2. Three nonmetallic elements in the period 2.
Ans i. Nitrogen ii. Oxygen iii. Fluorine

3. The element with electronic configuration (2, 7).
Ans Fluorine

4 Write the name and symbol of the element from the description. The atom has the smallest size.
Ans Helium (He)

5. Halogen in the period 3.
Ans Chlorine

6. Three elements with filled outermost shell.
Ans i. Helium ii. Neon iii. Argon

7. An alkaline earth metal in the period 3.
Ans Magnesium

8 Write the name and symbol of the element from the description. The atom having the smallest atomic mass.
Ans Hydrogen (H )

9. The family of metals having valency one.
Ans Alkali metals.

10 what does 4 and 9 indicate
Ans 4 – Atomic Number

9 – Atomic Mass
11 An alkali metal in period 3 which dissolves in water giving a strong alkali.
Ans Sodium

12. Two elements having a single electron in their outermost shell.
Ans:  Hydrogen, sodium.

13. Give the name and symbol of elements which occupy following positions in periodic table : Period 3 Group 14
Ans Silicon (Si)

14 Three elements having 7 electrons in their outermost shell.
Ans:  i. Fluorine ii. Chlorine iii. Bromine

15. The family of nonmetals having valency one.
Ans:  Halogens.

16 Write the name and symbol of the element from the description. The noble gas with the smallest atomic nucleus.
Ans Helium (He)

17. The periods which contain inner transition elements.
Ans Period 6 and Period 7

18. In the modern periodic table which are the metals among the first ten element
Ans Only Lithium, Beryllium

19 Name three transition elements
Ans Cobalt, Copper, Nickel

20 The family of metals having valency two.
Ans Alkaline earth metals.

21 The period with electrons in the shells K, L and M.
Ans Period 3.

22. Give the name and symbol of elements which occupy following positions in periodic table :
Period 2 Group 13
Ans Boron (B)

23. Give the name and symbol of elements which occupy following positions in periodic table : Period 3Group 0
Ans Argon (Ar)

24 The group with valency zero.
Ans Group 18.

25. Horizontal rows in modern periodic table.
Ans Periods

26. Give the name and symbol of elements which occupy following positions in periodic table :
Period 2Group 16
Ans Oxygen (O)

27. An alkali metal in the period 2.
Ans Lithium

28 Write the name and symbol of the element from the description. The most reactive nonmetal.
Ans Fluorine (Fe).

29. Write the name and symbol of the element from the description. The most electronegative atom.
Ans Fluorine (F )

30. The elements in periods 2 and 3 having stable electronic configuration.
Ans i. neon ii. Argon

Q.8 Give scientific reasons :

1. As we move down the group metallic character increases.
Ans i. As we move down the group the atomic size increases due to the addition of shells.
ii. The outermost shell goes far from the nucleus and valence electrons are held very weakly.
iii. These electrons can be easily donated by the atom to acquire a state octet structure and hence it becomes more metallic in character.

2. Metallic properties of the elements change to non metallic properties as one moves from left to right in a period of periodic table.
Ans i. If an element donates its valence electrons with ease so as to form positively charged ions, it is said to be metallic element.
ii. Conversely, if an element accepts electrons in its valence shell so as to form negatively charged ions, the element is said to be non metallic.
iii. On progressing from left to right, there is gradual increase in the nuclear change due to an increase in atomic number but this results in decrease in atomic size.
iv. Increased nuclear charge bounds the electrons in the valence shell more tightly and makes it difficult for atoms of elements do donate electrons. Thus the character of elements gradually changes from metallic to non-metallic.

3. The Law of Octaves is compared to musical notes.
Ans i. Newland found that on arranging the elements in increasing order of their atomic masses, every eighth element had properties similar to those of the first.
ii. In a musical scale also every eighth note is similar to first note so he called his law as the law of octaves.

4. The third period contains only eight elements even though the electron capacity of the third shell is 18.
Ans:  i. According of the law of electron octet, The last shell cannot have more than eight electrons.
ii. Hence, the third period contains only eight elements in the third shell even though the electron capacity of the third shell is 18.

5. Inert or noble gases have zero valency. 2
Ans i. Inert or noble gases neither lose or gain electrons. They have stable configuration.
ii. Thus, their octet is complete.
iii. Therefore, Inert or noble gases have zero valency.

6. The atomic size increases as the move down the group.
Ans i. Atomic radius is the distance between the nucleus of the atom and its outermost shell.
ii. Therefore, the atomic size increases as we move down the group because the number of shells increases and hence the atomic radius increases.

7. Elements belonging to the same group have the same valency.
Ans i. Elements fall in same group with similar properties.
ii. So, all the element that have same number of valance electrons belongs to the same group.
iii. Thus, Elements belonging to the same group have the same valency.

8. Alkali metals are good reducing agents.
Ans i. Alkali metals have one electrons in their valence shell.
ii. They easily lose or donate electrons.
iii. So alkali metals are good reducing agents.

9. Atomic size goes on decreasing while going from left to right within a period.
Ans i. As we go from left to right within a period, the atomic number increase one by one i.e the positive charge on nucleus increase one at a time.
ii. However, the additional electron gets added to the same outer most shell. ( no of shells across the period are same)
iii. Due to the increased nuclear change the electrons are pulled towards the nucleus to a greater extent and therefore the size of atom decreases.

Q.9 Solve Numerical problems. :

1. In Doberiner’s triads Li, Na, K, the atomic masses of Lithium and Potassium are 6.9 and 39.1 respectively,
then what will be the atomic mass of sodium.
Ans:  Atomic mass of sodium   = Atomic mass of Li + atomic mass of K / 2.
At mass of Na                          =  At. mass of Li + At. mass of K/2 
                                                =  6.9 +39.1 / 2
                                                 = 46 / 2  = 23
2 Show how Dobereiner’s Triad Law holds true for the following :
i. Li (6.9) Na (23.0) K (39.1)
ii. Ca ( 40.1) Sr (88.7) Ba (137.3)
Ans : Na =  6.9   +  39.1 / 2    =  23. 0
           Sr  = 40.1 +  137.3 / 2  =  88. 7 

Q.10.Writeproperties/characteristic /uses / advantages / effects. 

1 State the limitation of Dobereiner’s Law of Triad.
Ans i. His method did not hold true for all the elements.
ii.Properties of elements grouped into triads were not similar to each other.

2. Position of isotopes in Mendeleevs and the modern periodic table.
Ans:  Isotopes were discovered long time after Mendeleev put forth the periodic table. As isotopes have the same chemical properties but different atomic masses, a challenge was possed in placing them in the Mendleev periodic table. In modern periodic table the elements are arranged in accordance with their atomic number so position of isotopes is clear.

3.  Give two properties of noble gases.
Ans i. They are very inert.
ii.They are present in extremely low concentrations in our environment.

4 .State two merits of modern periods table ?
Ans i. The classification in based on the fundamental property of elements i.e atomic number.
ii.It relates the position of element to its electronic configuration in the valence shell and hence the elements have similar chemical properties.

5. State the limitations of Newlands Law of Octave.
Ans i. His law did not have the provision to accommodate newly discovered elements.
ii. Law was applicable only up to Calcium.
iii.He placed elements with different properties under the same note in octaves eg. Co and Ni are metals but they were placed with chlorine (which is a halogen.)

6. Write merits of mendeleev’s periodic table.
Ans i. Atomic masses of some elements were revised so as to give them proper place in the periodic table in accordance with their proportion.
ii. A number of gaps were left in the table for undiscovered elements. These properties were predicated from known neighbors. These predicted properties later matched well with the discovered elements.
iii. Mendeleev created the ‘zero’ group without disturbing the original periodic table in which the noble gases
were fitted very well.

7. State two demerits of modern periodic table?
Ans i. The position of hydrogen is unresolved
ii. It fails to accommodate lanthanides and actinides in the main body of the table.

8. State the demerits of Mendeleev’s periodic table.
Ans i. Mendeleev periodic table could not justify position of certain elements, rare earth and isotopes.
ii. When elements are arranged in an increasing order of atomic masses, the rise in atomic mass does not appear to be uniform.
iii.So it was not possible to predict how many elements could be discovered between two heavy elements.

Q.11 Write Short Notes :

1 Write short note on structure of the modern periodic table.
Ans: i. The modern periodic table consists of seven horizontal rows called the periods and eighteen vertical columns called the groups.
ii. The arrangement of the periods and groups results in the formation of boxes, where each box corresponds to the position of an element.
iii. In addition to these seven rows, lanthanide and actinide series are shown separately at the bottom of the periodic table. The first row is lanthanide series and the second row is actinide series.
iv. The entire periodic table is divided into four blocks: s-block, p-block, d-block and f-block.
v.A zig-zag line is drawn in the p-block of the periodic table. Metals lie on the left side while nonmentals lie
on the right side of this line. Metalloids lie along the border of this line.

2 Write short note on Mendeleev’s periodic law.
Ans i. Mendeleev organized the period table on the basis of the chemical and physical properties of the
elements. `
ii. For this purpose, he considered the molecular formulae of hydrides and oxides of the elements, melting
points, boiling points and densities of the elements and their hydrides and oxides.
iii. When he arranged the 63 elements known at that time in the increasing order of their atomic masses, he
found that the chemical and physical properties of elements showed repetition after certain fixed interval.
iv. On the basis of this finding, he stated that ‘properties of elements are a periodic function of their atomic
masses. This is known as Mendeleev’s periodic law.

Q.12 Chemical reactions with equations. 

1 Write down the electronic configuration of the following elements from the given atomic numbers. Answer the
following question with explanation.
a. A1, Si, Na, Mg, S
Which of the above elements has the highest metallic character?
b. C, Li, F, N, O
Which of the above elements has the highest nonmetallic character?

  Element Electronic configuration
i. 13Al 2, 8, 3
  14Si 2, 8, 4
  11Na 2, 8, 1
  12Mg 2, 8, 2
  16S 2, 8, 6

The element with the highest metallic character is 11Na.

  Element Electronic configuration
ii. 6C 2, 4
  3Li 2, 1
  9F 2, 7
  7N 2, 5
  8O 2, 6

The element with the highest nonmetallic character is 9F

Q.13.  Complete the given flow chart / table / diagram     

  1   State the electron capacity of shells and complete the table.

Shell No. Shell Electron Capacity
1 K ……………
2 L ……………
3 M ……………
4 N ……………

Ans: 

Shell No.

Shell Electron Capacity
1 K 2
2 L 8
3 M 18
4 N 32

 

Q.14 Laws/define/principles :

1 Write two similarities between lanthanides and actinides series.
Ans i. Lanthanides and actinides series are both part of f block elements.
ii. All the elements in both series are known as Inner Transition Elements.
iii. Both series have 14 elements each.

2 State Newland law of octaves.
Ans i. Newland arranged the elements in an increasing order of their atomic masses.
ii. He found that every eighth elements had properties similar to those of the first as in an octave of music.
iii.Music octaves sa, re, ga, ma, pa, dha, ni, sa

Q.15 Distinguish between 

1 Cations And Anions

  Cations Anions
i. They are positively charged ions They are negatively charged ions
ii. Formed by donating electrons Formed by gaining electrons
iii. Metal atoms form cations Non metal atoms form anions

 

2] Mendeleev periodic table and Modern periodic table 

  Mendeleev periodic table Modern periodic table
1 Elements were arranged in the increasing order of their atomic masses Elements were arranged in the order of their atomic number.
2 Mendeleev’s table could not justify the position of certain elements, rare earth and isotopes. Modern periodic table could remove most of the defects of Mendeleev periodic table.

3. Alkali metals And Halogens

  Alkali metals Halogens
i. Group 1 elements are known as alkali elements Group 17 elements are known as halogens
ii. Highly electron positive Highly electron negative
iii. Strong reducing agents Strong oxidizing agents
iv. Good conductors of heat and electricity Bad or non conductors of heat and electricity

4. Lanthanide series and Actinide Series

  Lanthanides series Actinides series
i. It belong to period 6 It belongs to period 7
ii. They are rare earth elements They are radio active elements

5. Electrons And Protons

 

 

i.

Electrons Protons
It is negatively charged It is positively charged
ii. Revolves around the nucleus of atom in the shells Present in the nucleus of atom

6. Atomic Number and Mass Number

  Atomic Number Mass Number
 

i.

 

ii.

It is the number of protons present in the nucleus of atom or the number of electrons revolving around the nucleus. It is the sum of protons and neutrons in nucleus of an atom.
It is denoted by letter Z. It is denoted by letter A.

7. Groups and Periods

  Octet Duplet
 

i.

Arrangement of having 8 electrons in outermost shell is known as octet rule. Arrangement of having 2 electrons in outermost shell is known as duplet rule.
    Helium is the only noble gas which obeys duplet rule.
ii. All noble gases except helium obey this rule.
   

8 Groups and Periods

  Groups Periods
  These are 18 vertical columns in modern periodic table  
i. These are 7 horizontal rows in modern periodic table
   
  Group number predicts the number valence electron  
ii. Period predicts the number of shells
   
  Elements in the same group have same chemical properties. Elements change from metallic to non metallic while going form left to right across period.
iii.
 

9. Halogens And Noble gases

  Halogens Noble gases
i. They belongs to group 17 They belong to group 18
  They have 7 electrons in their outer most shell They have 8 electrons in their outer most shell only helium has two electrons
ii.
 
iii. Very reactive Do no react at all or unreactive
iv. Form anions Have stable electronic configuration. Do not form ions.

10 . Metals And Non-Metals

  Metals Non Metals
i. Have 1 or 2 valence electron Have 4, 5, 6 or 7 valence electron
ii. Forms cations by losing valence electron Forms anion by gaining electron
iii. Present in group 1 and 2 Present in group 13, 14, 15
iv. They are electron positive They are electron negative
v. Placed on the left side of periodic table Placed on right side of periodic table
vi. Good conductors of heat Bad or non-conductors of heat

Q.16 Give examples :  

1 Give examples : 3 Noble gases and state their groups.
Ans Helium, Neon, Argon Group 18 Or Group 0

2 Give examples : 3 Halogens and state their groups.
Ans Flourine, Chlorine , Bromine Group 17

3 Give examples : 3 Alkali metals and state their groups.
Ans Lithium, Sodium, Potassium Group 1

4 Give example : 3 Alkaline Earth metals and state there groups.
Ans Beryllium, Magnesium, Calcium Group 2

Q.17 Give explanation using the given statements :   

  1. An element has its electron configuration as 2,8,8,2. Now answer the following questions.
    i. What is the atomic number of this element?
    ii. What is the group of this element?
    iii. To which period does this element belong?
    Ans i. The atomic number of this element is 20.
    ii. The group of this element 2.
    iii. This element belongs to fourth period.

2. Read the statements given below. Identify and write the concept upon which the given statement is based.
Ans: i. The atomic mass of the middle element was approximately equal to the mean of the atomic masses of
other two elements. What are these elements know as
ii. This law was found to be applicable only upto calcium. Identify the law.
iii. Mendleev created the group to fit noble gases.
iv. The position of this element is still ambigous.
v. Two series are part of periodic table but yet separated and show at the bottom.
vi. These elements lie along the border of this zig-zag line in periodic table.
Ans:  i. Doberiner’s Triads
ii. Newland’s Law of Octaves
iii. ‘Zreo’ group
iv, Hydrogen
v. Lanthanide series and actinide series
vi. Metalloid.

3. An element has its electronic configuration as 2,8,2. Now answer the following questions.
i. What is the atomic number of this element ?
ii. What is the group of this element ?
iii.To which period does this element belong ?
iv.With which of the following elements would this element resemble N(7), Be(4), Ar(18), Cl(17)
Ans i.  1 2
        ii.  2
        iii. 3rd
        iv. Be(4) as they belong to the same group.

Q.18. Complete the table / chart.     

Complete the list of the first 20 elements of the periodic table indicating groups and periods.

1 ……… 2 13 14 15 …….. 17 He
2 Li ……….. B C N O F Ne
3 Na Mg Al ……….. P S ……….. Ar
4 ……..              

Ans: 

1 H 2 13 14 15 16 17 He
2 Li Be B C N O F Ne
3 Na Mg Al Si P S Cl Ar
4 K              

2.  Write the electronic configuration of given elements and state your observation based on       

Elements Electronic Configuration
Li ……………
Be ……………
C ……………
N ……………
O ……………
F ……………

                                         Ans:

Elements Electronic Configuration
Li 2,1
Be 2,2
C 2,4
N 2,5
O 2,6
F 2,7

Observation

Elements in some group have some number of valance electron.

Li = 2, 1 Be = 2, 2 C = 2, 4 N = 2, 5 O = 2, 6 F= 2,7 Elements in same period have same number of shells.

3. Complete the table :

Name Of Element Atomic Number Electronic Configuration
    K L M N
Hydrogen 1
Lithium 3
Sodium 11
Potassium 19

Ans:

Name Of Element Atomic Number Electronic Configuration
    K L M N
Hydrogen 1 1
Lithium 3 2 1
Sodium 11 2 8 1
Potassium 19 2 8 8 1

4. Match each item with the correct statement below.

      Elements that have properties of both metals and non-metals; located near the stair-step line.
i. Halogens a.
     
ii. Alkaline earth metals b. Reactive elements of group 17 that are poor conductors.
iii. Transition metals c. Highly reactive elements that belong to group 1.
  Semi conductors / metalloids   Very stable due to the fact that they have a full outer most energy level.
iv. d.
   
v. Alkali metals e. Elements that belong to group 3-12 and are somewhat reactive.
vi. Noble gases f. Group 2 elements have two valence electrons.

Ans: 

i. Halogens b.Reactive elements of group 17 that are poor conductors.
ii. Alkaline earth metals f. Group 2 elements have two valence electrons.
iii. Transition metals e. Elements that belong to group 3-12 and are somewhat reactive.
  Semi conductors / metalloids a. Elements that have properties of both metals and non metals; located near the stair step line.
iv.
 
v. Alkali metals c. Highly reactive elements that belong to group 1

vi.

Noble gases d. Very stable due to the fact that they have a full outer most energy level.

Q.19 Write laws, theories and explain. 
1 State Dobereiners Law of Triads ?
Ans:  Dobereiners was a German scientist who suggested that properties of elements are related to their atomic masses.
i. He made group of three elements each having similar chemical properties.
ii. The three elements in a triad were in increasing order of their atomic mass.
iii.The atomic mass of the middle element was approximately equal to the mean of atomic masses of the other two elements.

Q.20 Complete the paragraph. 
(two, eighteen, very long, eight, 32, short, long, longest)
The first period has …………… elements and is called shortest period. The second and there periods
have …………… elements and all called …………… period. The fourth and fifth period has …………… elements
and are called long period. The sixth period has thirty two elements and is …………… period seventh period
has …………… elements.
Ans :  The first period has two elements and is called shortest period. The second and there periods have eight
elements and all called short period. The fourth and fifth period has eighteen elements and are called long
period. The sixth period has thirty two elements and is very long period seventh period has 32 elements.

Q.21 Write answers based on given diagram/figure :
1 The following is new land’s octave table. Observe it and answer the following questions.

Sa (do) Re (re) Ga (mi) Ma (fa) Pa (so) La (dha) Ni (ti)
H Li Be B C N O
F Na Mg Al Si P S
D K Ca Cr Ti Mn Fe
Co & ni Cu Zw Y In As Se
Br Rb Sr Ce and Zr
      La      

i. Which of the elements in 1 column has different properties from rest of the elements.
ii. Which of the elements resemble with each other in second column.
iii.Pick up odd elements in the second last column.
iv.Pick up elements which have similar properties in last column.
Ans i. Co and Ni
ii. Na and K
iii. Mn
iv. O, S, Se

2 Study the radius of the element given below and answer the following questions.

Elements K Na Rb Cs Li
Atomic radius (pm) 231 186 244 262 152

i. Which of above element have smallest atom?
ii. In which group of modern periodic table the above element are belongs?
iii.What is the periodic trend observed in the variation of atomic radii down a group?
Ans i. Li
ii. first group
iii.while going down a group atomic radius goes on increasing. As a result, atomic size increases.

3. Observe the figure and answer the following questions.
i. Identify the block shown by box A and write an electronic configuration of any one element of this block.
ii. Identify the block of element denoted by the letter B and write .its period numberperiodic table Ans i. The block shown by box A is s-Block.
Na(11) = 2, 8, 1 (electronic configuration of any element in s block)
ii.The block of element denoted by letter B is d – Block.
The period number of that element is 4.

Q.22 Answer the following :
1 How could the modern periodic table remove Various Anomalies of Mendeleev’s Periodic Table?
Ans:  Various Anomalies of Mendeleev’s Periodic Table were removed in the following ways.
i. The position for all isotopes of an elements justified since they have same atomic number.
ii. The position of certain elements which are earlier misfit type Co – 58 .9 was placed before Ni – 58.7 are now justified because CO has Lower Atomic Number Than Ni.
iii.Cause of periodicity explained due to same electronic configuration repeated after certain gap.

2. Explain how Mendeleev’s contribution laid the foundation of Modern Periodic Table.
Ans i. Mendeleev arranged the elements in the increasing order of there atomic masses.
ii. He arranged it in table format with, horizontal Roues called Periods and Vertical Columns called Groups.
iii.Elements in the same group had same valency and similar chemical properties.
iv.A number of gaps were left in the table for under discovered elements. There properties were predicted
from known neighbours. These predicted properties later matched well with The Discovered Elements.
v. Atomic Masses of same elements were revised so as to give them proper place in the periodic table in
accordance with their properties. Eg. Atomic Mass of Beryllium was 14.09; It was changed to 9.4 and
Beryllium was placed before Boron.

3. Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with explanation.
a. 3Li, 14Si, 2He, 11Na, 15Which of these elements belong to be period 3?
b. 1H, 7N, 20Ca, 16S, 4Be, 18Ar
Which of these elements belong to the second group?
c. 7N, 6C, 8O, 5B, 13A1 Which is the most electronegative element among these?

  Element Electronic configuration
i. 3Li 2, 1
  14Si 2, 8, 4
  2He 2
  11Na 2, 8, 1
  15P 2, 8, 5

The elements 14Si, 11Na and 15P belong to period 3

  Element Electronic configuration
ii. 1H 1
  7N 2, 5
  20Ca 2, 8, 8, 2
  16S 2, 8, 6
  4Be 2, 2
  18Ar 2, 8, 8

The elements 20Ca and 4Be belong to second group as they have two valence electrons.

  Element Electronic configuration
iii. 7N 2, 5
  6C 2,4
  8O 2, 6
  5B 2, 3
  13Al 2, 8, 3

The most electronegative element is 8O.   

 4.  Among the elements P (At.  No. 14), Q ( At. No. 6), R            ( At No 15). Which elements have similar chemical properties and why?                                                                 Ans:  P  (14) 2, 8, 4
           Q  (6)  2, 4
            R (15) 2, 8, 5
Elements P and Q have similar chemical properties as they have same number of valence electrons.


5 . Write down the electronic configuration of the following elements from the given atomic numbers. Answer the
following question with explanation.
a.
4Be, 6C, 8O, 5B, 13Al Which is the most electropositive element among these?

b.11Na, 15P, 17Cl, 14Si, 12Mg Which of these has largest atoms?
c.
19K, 3Li, 11Na, 4Be Which of these atoms has smallest atomic radius?

a. Element Electronic configuration
  4Be 2, 2
  6C 2, 4
  8O 2, 6
  5B 2, 3
  13Al 2, 8, 3

The most electropositive element is 13Al.

b. Element Electronic configuration
  11Na 2, 8, 1
  15P 2, 8, 5
  17Cl 2, 8, 7
  14Si 2, 8, 4
  12Mg 2. 8. 2

The element which has the largest atom is 11Na.

c. Element Electronic configuration
  19K 2, 8, 8, 1
  3Li 2, 1
  11Na 2, 8, 1
  4Be 2, 2

The element with the smallest atomic radius is 4Be.     

Q.23 Answer the following in detail :
1. Atomic number of few elements are given below 10, 20, 7, 14
i. Identify The Elements
ii. Identify The Group Number
iii.Identify The Period
iv.State Their Electronic Configuration
v. Determine The Valency of There Elements
Ans i. 10 -Neon
20 -Calcium
7- Nitrogen
14 -Silicon
ii. Neon – Group 18
Calcium – Group 2
Nitrogen -Group 15
Silicon – Group 14
iii. Neon – Period 2
Calcium – Period 4
Nitrogen -Period 2
Silicon – Period 3
iv. Neon – 2, 8
Calcium – 2, 8, 8, 2                                                             Nitrogen -2, 5
Silicon – 2, 8, 4
v. Neon O Valency
Calcium 2
Nitrogen 3
Silicon 4

2. 

Li Be   B C N O F Ne

i. List the group to which following elements belong.
ii. Name the period to which they belong.
iii.Depending upon these electronic configuration justify there period.
iv.Name a Metal, Non Metal, Halogen and a Noble Gas.
v. When we move across the period from left to right, how the metallic character change.
Ans:  i. Li – Group 1
Be -Group 2
B – Group 13
C – Group 14
N – Group 15
O – Group 16
F – Group 17
Ne -Group 18
ii. Period – 2
iii.Li – 2,1
C – 2, 4
F – 2, 7
Electronic configuration clearly shows that all the elements have two electron shells . Hence they belong to
2nd period
iv. Metal – Lithium (N)
Non Metal – Nitrogen (N)
Halogen – Fluorine (F)
Noble gas – Neon (Ne)
v. When we move across the period from left is to right then metallic character decreases and non metallic
character increase
Metal –>Non Meta

3.

Elements P Q R
Mass Number 23 20 35
Number Of Neutrons 12 10 18

i. Arrange the above elements in a decreasing order of their atomic radii.
ii. State the period to which the above elements belong.
iii. Why this arrangement of elements is similar to the above period of modern periodic table ?
iv. Which of the above elements have the biggest and the smallest atom?
v. What is the periodic trend observed in the variation of atomic radius while going from left to right within a
period ?Ans i. Li, Be, B, C, N, O
ii. 2 period
iii. All the elements have 2 shells in electronic configuration.
iv. Biggest – Lithium, Smallest – Oxygen.
v. Atomic radius goes on decreasing from Left to right.

7. On the basis of electronic configuration around the nucleus, how will you identify?
i. Chemically Similar Elements.
ii. First Elements of A Period.
iii.It belongs to Alkali Metals
iv.A Group of Halogen.
v. A Group of inert Gases.
Ans:  i. The elements having the same number of valence electron are chemically similar.
ii. The elements having one electron in its valence shell is the first element of a period.
iii.The elements having one electron in their valence shells belong it Alkali Metals.
iv.The elements having seven electrons in their valence shells belong to halogens.
v. The elements having eight electrons in their valence shells belong to inert Gases exception is helium which has only two electrons in its valence shell.

8 . Study the following and answer.

H
Li
……..
……..
Rb
Cs
Fr

i. Fill in the missing blocks ?
ii. Give the electronic configuration of any 3 elements and what similarity do you observe ?
iii.Identify the group to which all these elements belong with reason ?
iv.What special name to given to the group ?
v. To which block does the group belong from S,P,D or F block ?
Ans i. Na , K
ii. Li – 2, 1
Na – 2, 8, 1
K – 2, 8, 8, 1
all the elements have one electron in their valence shell.
iii. They all belong to group 1 as all have 1 valence electron.
iv. Alkali Metals
v. S Block

9. An element has its electron configuration as 2,8,2. Now answer the following questions.
i. What is the atomic number of this element?
ii. What is the valency of this element?
iii. What is the group of this element?
iv. To which period does this element belong?
v. With which of the following elements would this element resemble?(Atomic numbers are given in the
brackets)
N(7), Be(4), Ar(18), CI(17)
Ans i. Atomic number 12
ii. Valency 2
iii. Group 2
iv. Period 3
v. The element would resemble (Chemically similar) beryllium (Be) with electronic configuration (2, 2). As both possess a same number of valence electrons, both would lie in the same group and display similar chemical properties.

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