Q.1 Textbook activity question :

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

Ans:

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

2 There are some vacant places in the Mendeleev’s periodic table. In some of these places the atomic masses are seen to be predicted. 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:

i] atomic mass = 44, group III and period 4

ii] Atomic mass = 68, group III and period 5

iii] Atomic mass = 72, group IV and period 5

 

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 Arrange the above elements vertically downwards in an increasing order of atomic radii.

Element	K	Na	Rb	Cs	Li
Atomic radius (pm)	231	186	244	262	151

Ans:   Elements  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 are same which is 1.

6. Chlorine has two isotopes,viz, Cl-35 and Cl- 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 ³⁵₁₇Cl and ³⁷₁₇Cl 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 (⁵⁹Co) and nickel (⁵⁹Ni) 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.

i. 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.

ii. The modem Periodic table resolved this problem. According to the Modem Periodic law, elements are arranged in their increasing order of atomic number.

iii. 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 ⁵³₂₄Cr and 24manganese ⁵⁵₂₅Mn ? 

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 the group 1 of the modern periodic table.

20. What do you think? Should hydrogen be placed in the group 17 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 (H₂O) just like oxides of alkali metals (Na₂O, K₂O). It has the same common charge ( + 1) as all alkali metals.

ii. It resembles halogens in forming diatomic molecules H₂, Cl₂, F₂, Br₂.

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 are 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 the period-2. Write down 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
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 the 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 14

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. H₂, N₂, O₂

Ans Option c.

c. Li, Na, K d. Na, Bx, Ax

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.

i. It has 18 horizontal rows known as periods

ii. It has 7 vertical columns known as periods

iii. It has 18 vertical columns known as groups

iv. 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.

1. 1. Only physical properties
   2. Only chemical properties
   3. Both physical and chemical properties
   4. None of the above

Ans Option c.

1. 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.
   1. Germanium b. Chlorine c. Oxygen d. Silicon

Ans Option a.

Q.3. Find the odd one out 7

1. 1Nitrogen, Neon, Argon, Helium

Ans Nitrogen. (The others are inert gases.)

1. 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.)

1. 3 Sodium, Aluminium, Chlorine, Carbon

Ans Carbon (Carbon belongs to the second row, while the others belong to third row)

1. 4. Temperature, Conduction, Convection, Radition

Ans Temperature (Others are modes of transfer of heat.)

1. 5. Cal/g, cal/g°C, kcal/kg.°C, erg/g.°C

Ans Cal/g [(Others are units) of specific heat capacity.]

1. 6 The joule, The erg, The calorie, The newton

Ans The newton [Others are units of energy (as well as work)]

1. 7 Fluorine, Sulphur, Bromine, Iodine

Ans Sulphur (Others are halogens)

Q.4. Find co-related terms 11

1. 1 Triads : :: Octaves : Group of 8 elements

Ans Triads : Group of 3 elements :: Octaves : group of 8 elements

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

Ans Dobereiner’s : Law of triad : : John Newland : Law of octaves 3. 3. Al : Al₂O₃ : : P : ……………

Ans Al : Al₂O₃ : : P : P₂O₅

1. 4. Potassium : : : Magnesium : Alkaline earth metal

Ans Potassium : Alkali metal : : Magnesium : Alkaline earth metal

1. 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

1. 6.Electro positivity : :: Electro negativity : Non metallic character

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

1. 7. Metals : Cation :: Non metal : ……………

Ans Metals : Cation :: Non metal : Anion 8 8.Sodium : Metal : : Chlorine : ……………

Ans Sodium : Metal : : Chlorine : Nonmetal

1. 9.Oxygen : Valency 2 : : Nitrogen : ……………

Ans Oxygen : Valency 2 : : Nitrogen : Valency 3

1. 10.Molecular formula of beryllium oxide : BeO : : Molecular formula of beryllium chloride : ……………

Ans Molecular formula of beryllium oxide : BeO : : Molecular formula of beryllium chloride : BeCl₂

1. 11. Eka-Boron : : : Eka-Aluminium : Gallium (Ga)

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

Match the pair 8

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

Column “A”	Column “B”

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

8

Column “A”	Column “B”
i. Eka- Boron	a. Germanium
ii. Eka- Aluminium	b. Silicon
	c. Scandium
	d. Gallium

Ans

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

Q.6. State True or False 5

1. 1.All the 118 elements are now discovered.

Ans All the 118 elements are now discovered – True

1. 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

1. 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

1. 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

1. 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 30

1. 1.The three metals in the third period of the modern periodic table.

Ans i. Sodium ii. Magnesium iii. Aluminium

1. 2.Three nonmetallic elements in the period 2.

Ans i. Nitrogen ii. Oxygen iii. Fluorine

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

Ans Fluorine

1. 4.Write the name and symbol of the element from the description. The atom having the smallest size.

Ans Helium (He)

1. 5.Halogen in the period 3.

Ans Chlorine

1. 6.Three elements with filled outermost shell.

Ans i. Helium ii. Neon iii. Argon

1. 7.An alkaline earth metal in the period 3.

Ans Magnesium

1. 8.Write the name and symbol of the element from the description. The atom having the smallest atomic mass.

Ans Hydrogen (H₂)

1. 9.The family of metals having valency one.

Ans Alkali metals.

4 Be what does 4 and 9 indicate

9

Ans 4 – Atomic Number 9 – Atomic Mass

1. 11.An alkali metal in period 3 which dissolves in water giving a strong alkali.

Ans Sodium

1. 12.Two elements having a single electron in their outermost shell.

Ans Hydrogen, sodium.

1. 13.Give the name and symbol of elements which occupy following positions in periodic table : Period 3Group 14

Ans Silicon (Si)

1. 14.Three elements having 7 electrons in their outermost shell.

Ans i. Fluorine ii. Chlorine iii. Bromine

1. 15.The family of nonmetals having valency one.

Ans Halogens.

1. 16.Write the name and symbol of the element from the description. The noble gas with the smallest atomic nucleus.

Ans Helium (He)

1. 17.The periods which contain inner transition elements.

Ans Period 6 and Period 7

1. 18.In the modern periodic table which are the metals among the first ten element

Ans Only Lithium, Beryllium

1. 19.Name three transition elements

Ans Cobalt, Copper, Nickel

1. 20.The family of metals having valency two.

Ans Alkaline earth metals.

1. 21.The period with electrons in the shells K, L and M.

Ans Period 3.

1. 22.Give the name and symbol of elements which occupy following positions in periodic table : Period 2Group 13

Ans Boron (B)

1. 23.Give the name and symbol of elements which occupy following positions in periodic table : Period 3Group 0

Ans Argon (Ar)

1. 24The group with valency zero.

Ans Group 18.

1. 25.Horizontal rows in modern periodic table.

Ans Periods

1. 26.Give the name and symbol of elements which occupy following positions in periodic table : Period 2Group 16

Ans Oxygen (O)

1. 27.An alkali metal in the period 2.

Ans Lithium

1. 08.Write the name and symbol of the element from the description. The most reactive nonmetal.

Ans Fluorine (Fe).

1. 29.Write the name and symbol of the element from the description. The most electronegative atom.

Ans Fluorine (F₂)

1. 30The elements in periods 2 and 3 having stable electronic configuration.

Ans i. neon ii. Argon

Give scientific reasons 18

1. 1.As we move down the group metallic character increases.

Ans i. As we move down the group the atomic size increases due to addition in shells.

1. The outer most shell goes far form the nucleus and valence electrons are held very weakly.
2. These electrons can be easily donated by the atom to acquire a state octet structure and hence it becomes more metallic in character.
3. 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 changed ions, it is said to be metallic element.

1. 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.
2. On progressing from left to right, there is gradual increase in the nuclear change due to increase in atomic number but this results in decrease in atomic size.
3. 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.

1. 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 law of octaves.

1. 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.

1. 2.Inert or noble gases have zero valency.

Ans i. Inert or noble gases neither lose or gain electrons. They have stable configuration.

1. Thus, their octet is complete.
2. Therefore, Inert or noble gases have zero valency.
3. 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.

1. 7.Elements belonging to the same group have the same valency.

Ans i. Elements fall in same group with similar properties.

1. So, all the element that have same number of valance electrons belongs to the same group.
2. Thus, Elements belonging to the same group have the same valency.
3. 8.Alkali metals are good reducing agents.

Ans i. Alkali metals have one electrons in their valence shell.

1. They easily lose or donate electrons.
2. So alkali metals are good reducing agents.
3. 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.

1. However, the additional electron gets added to the same outer most shell. ( no of shells across the period are same)
2. 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. 4

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 Lithium + Atomic mass of Potassium

2

At mass of Na = At mass of Li + At mass of K

2

6.9 + 39.1

=

2

= 46 = 23

2

1. 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 =

Sr =

6.9+39.1

2

40.1+137.3

2

= 23. 0

= 88. 7

Q10 Write properties/characteristic/uses/advantages/effects. 16

1. 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.

1. 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.

1. 3.Give two properties of noble gases.

Ans i. They are very inert.

ii.They are present in extremely low concentrations in our environment.

1. 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.

1. 5.State the limitations of Newlands Law of Octave.

Ans i. His law did not have the provision to accommodate newly discovered elements.

1. Law was applicable only up to Calcium.
2. 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.)
3. 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.

1. A number of gaps were left in the table for undiscovered elements. These properties were predicated from known neightbours. These predicted properties later matched well with the discovered elements.
2. Mendeleev created the ‘zero’ group without disturbing the original periodic table in which the noble gases were fitted very well.
3. 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.

1. 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 appears to be uniform.

III. So it was not possible to predict how many elements could be discovered between two heavy elements.

Write Short Notes 4

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.

1. 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. `

1. 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.
2. 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.
3. 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.11. Chemical reactions with equations. 2

1 Write down the electronic configuration of the following elements from the given atomic numbers. Answer the following question with explanation.

A. ₁₃A1, ₁₄Si, ₁₁Na, ₁₂Mg, ₁₆S

Which of the above elements has the highest metallic character? B. ₆C, ₃Li, ₉F, ₇N, ₈O

Which of the above elements has the highest nonmetallic character?

Ans

	Element	Electronic configuration
i.	13A1	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. 12 ..Complete the given flow chart / table / diagram 2

1 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

• 1. Q13. Laws/define/principles 4

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.

1. 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. 14.Distinguish between 20

1. Cations And Anions

Ans

	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

1. 2. Mendeleev periodic table and Modern periodic table

Ans

	Mendeleev periodic table	Modern periodic table

i.	Elements were arranged in the increasing order of their atomic masses.	Elements were arranged in the order of their atomic number.
	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.
ii.

1. 3. Alkali metals And Halogens

Ans

	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

1. 4. Lanthanide series and Actinide Series

Ans

	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

1. 5. Electrons And Protons

Ans

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

1. 6. Atomic Number and Mass Number

Ans

	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.

1. 7. Octet and Duplet

Ans

	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.

1. 8. Groups and Periods

Ans

	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.

1. 9. Halogens And Noble gases

Ans

	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.

1. 10. Metals And Non Metals

Ans

	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

• 1. Q15. Give examples 8

1. 1.Give examples : 3 Noble gases and state their groups.

Ans Helium, Neon, Argon Group 18 Or Group 0

1. 2.Give examples : 3 Halogens and state their groups.

Ans Flourine, Chlorine , Bromine Group 17

1. 3.Give examples : 3 Alkali metals and state their groups.

Ans Lithium, Sodium, Potassium Group 1

1. 4.Give example : 3 Alkaline Earth metals and state there groups.

Ans Beryllium, Magnesium, Calcium Group 2

Q16.Give explanation using the given statements 9

1. 1.An element has its electron configuration as 2,8,8,2. Now answer the following questions.
   1. What is the atomic number of this element?
   2. What is the group of this element?
   3. To which period does this element belong?

Ans i. The atomic number of this element is 20.

1. The group of this element 2.
2. This element belongs to fourth period.
3. 2.Read the statements given below. Identify and write the concept upon which the given statement is based.
   1. 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
   2. This law was found to be applicable only upto calcium. Identify the law.
   3. Mendleev created the group to fit noble gases.
   4. The position of this element is still ambigous.
   5. Two series are part of periodic table but yet separated and show at the bottom.
   6. These elements lie along the border of this zig-zag line in periodic table.

Ans i. Doberiner’s Triads

1. Newland’s Law of Octaves
2. ‘Zreo’ group iv, Hydrogen
3. Lanthanide series and actinide series
4. Metalloid.
5. 3.An element has its electronic configuration as 2,8,2. Now answer the following questions.
   1. What is the atomic number of this element ?
   2. What is the group of this element ?
   3. To which period does this element belong ?
   4. With which of the following elements would this element resemble N(7), Be(4), Ar(18), Cl(17)

Ans i. 12

ii. 2 iii.3rd

iv.Be(4) as they belong to the same group.

Complete the table / chart. 12

1. 1. 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

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

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.

1. 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

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

• 1. Q18Write laws, theories and explain. 3

1 1.State Dobereiners Law of Triads ?

Ans Dobereiners was a German scientist who suggested that properties of elements are related to their atomic masses.

1. He made group of three elements each having similar chemical properties.
2. The three elements in a triad were in increasing order of their atomic mass.
3. The atomic mass of the middle element was approximately equal to the mean of atomic masses of the other two elements.

Q19.Complete the paragraph. 3

1 1. 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. 20.Write answers based on given diagram/figure 9

1. 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

• 1. Which of the elements in 1^st column has different properties from rest of the elements.
  2. 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

1. 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

• 1. Which of above element have smallest atom?
  2. In which group of modern periodic table the above element are belongs?
  3. What is the periodic trend observed in the variation of atomic radii down a group?

Ans i. Li

1. first group
2. while going down a group atomic radius goes on increasing. As a result, atomic size increases.
3. 3.Observe the figure and answer the following questions.
   1. Identify the block shown by box A and write an electronic configuration of any one element of this block.
   2. Identify the block of element denoted by letter B and write its period number.

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.

Q21. Answer the following 15

1. 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.

• 1. The position for all isotopes of an elements justified since they have same atomic number.
  2. 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.
  3. Cause of periodicity explained due to same electronic configuration repeated after certain gap.

1. 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.

1. He arranged it in table format with, horizontal Roues called Periods and Vertical Columns called Groups.
2. 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.

1. 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, ₁₅P

Which 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?

Ans

	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.

1. 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.

1. 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?

Ans

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 ₁₃A1.

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.

Q22.Answer the following in detail 45

1. . Atomic number of few elements are given below 10, 20, 7, 14

1. Identify The Elements
2. Identify The Group Number iii.Identify The Period
3. State Their Electronic Configuration
4. Determine The Valency of There Elements

Ans i. i. 10 -Neon

20 -Calcium

7- Nitrogen

14 -Silicon

1. ii. Neon – Group 18 Calcium – Group 2 Nitrogen -Group 15 Silicon – Group 14
2. iii. Neon – Period 2 Calcium – Period 4 Nitrogen -Period 2 Silicon – Period 3
3. iv. Neon – 2, 8 Calcium – 2, 8, 8, 2

Nitrogen -2, 5

Silicon – 2, 8, 4

1. v. Neon O Valency Calcium 2 Nitrogen 3 Silicon 4

2. 2.

Li

Be

B

C

N

O

F

Ne

1. List the group to which following elements belong.
2. Name the period to which they belong.
3. Depending upon these electronic configuration justify there period.
4. Name a Metal, Non Metal, Halogen and a Noble Gas.
5. 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 2^nd period

1. Metal – Lithium (N)

Non Metal – Nitrogen (N) Halogen – Fluorine (F) Noble gas – Neon (Ne)

1. When we move across the period from left is to right then metallic character decreases and non metallic character increase

Metal → Non Metal

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

Study The Table And Answer The Following.

1. Write the atomic number and electronic configuration of elements. P, Q and R
2. To which groups do P, Q, and R belong iii.To which period do P, Q And R belong

iv.Which among P, Q and R is (i) An Alkali Metal (ii) Noble Gas (iii) Halogen

Ans i. P

Mass number = 23 Neutron = 12

Atomic number = Mass number – Neutron

∴ 23 – 12 = 11 (electronic configuration 2,8,1) Q

Mass number = 20 Neutron = 10

∴ Atomic number = 20 – 10 = 10

Electronic configuration = 2, 8 R.

Mass number = 35 Neutron = 18

∴ Atomic number = 35 – 18 = 17

Electronic configuration = 2, 8, 7

ii. P Belongs to Group I

Q Belongs To Zero Group R Belong To Group 7

iii.P Belongs to 3^rd Period Q Belongs 2rd Period R Belong to 3^rd Period

iv.P is An Alkali Metal Q is A Noble Gas R is A Halogen

1.i. What is the symbol and used for elements francium in Periodic Table.

ii. To which group and period does it belong. iii.How many valence elections will it have.

1. It is a metal on a non-metal.
2. Name another element of the same group.

Ans i. Fr

1. Group 1 and period 7
2. valence electron 1 because it belongs to group 1
3. It is a metal
4. Sodium, Potassium
5. 4. In the periodic table given below, lithium, carbon oxygen and neon are placed in the correct positions and positions of nine other elements are represented by letter. There letters are not the symbol for the elements.

1	2	13	14	15	16	17	18
lithium			Carbon		oxygen	L	Neon
X			E		G	Q
Y						R
Z						T

• 1. Give the letter of the most reactive metal 1
  2. Give the letter for most reactive non metal 1
  3. Name the family of elements represented by L, Q, R, T 1
  4. Name one elements in each case occurring in group 2, 13 and 15 2

Ans i. Give the letter of the most reactive metal – Z

1. Give the letter for most reactive non metal – L
2. Name the family of elements represented by L, Q, R, T – halogens
3. Name one elements in each case occurring in group 2, 13 and 15

group 2 – calcium, group 13 – boron, group 15 – nitrogen

1. 5. Taking into consideration the period of the elements given below, answer the following questions :

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

• 1. Arrange the above elements in a decreasing order of their atomic radii.
  2. State the period to which the above elements belong.
  3. Why this arrangement of elements is similar to the above period of modern periodic table ?
  4. Which of the above elements have the biggest and the smallest atom ?
  5. 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

1. 2^nd period
2. All the elements have 2 shells in electronic configuration.
3. Biggest – Lithium, Smallest – Oxygen.
4. Atomic radius goes on decreasing from Left to right.
5. 6. On the basis of electronic configuration around the nucleus, how will you identify?
   1. Chemically Similar Elements.
   2. 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.

1. The elements having seven electrons in their valence shells belong to halogens.
2. 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.
3. 8. Study the following and answer.

Li

Rb Cs

Fr

H

• 1. Fill in the missing blocks ?
  2. 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 ?

1. What special name to given to the group ?
2. 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.

1. Alkali Metals
2. S Block
3. 9. An element has its electron configuration as 2,8,2. Now answer the following questions.
   1. What is the atomic number of this element?
   2. What is the valency of this element? iii.What is the group of this element?
4. To which period does this element belong?
5. 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

1. Period 3
2. The element would resemble (Chemically similar) beryllium (Be) with electronic configuration (2, 2). As both

possess same number of valence electrons, both would lie in the same group and display similar chemical properties.