Q & A of Periodic table

PERIODIC TABLE

1.     What is the fundamental property on which Mendeleev periodic table is based.

ANS: the Mendeleev periodic table is based on increasing order of atomic masses and similarity in the chemical properties of elements.

2.     State Mendeleev’s periodic law.

ANS: it states that the physical and chemical properties of the element are periodic function of their atomic mass.

3.     Name a group of elements which was not known when Mendeleev formulated his periodic table.

ANS: noble gases were not known.

4.     Name three elements for which Mendeleev left gap in his periodic table.

ANS:  Scandium, gallium, and Germanium

5.     List two anomalous pairs in Mendeleev’s periodic table.

ANS: i) Cobalt and Nickel      ii)  Tellurium and Iodine

6.     State modern periodic table.

ANS: it states that the physical and chemical properties of the element are periodic function of their atomic number.

7.     Mention the number of groups and periods in Mendeleev and Modern  periodic table is based.

ANS:   In Mendeleev’s periodic table there were 6 periods and VIII groups.

In Modern periodic table, there are 7 periods and 18 groups.

8.     Mention the number of valence electrons present in elements belonging to

(a)    Group 17  (b)  group 1     (c) group 16  (d) group 13

ANS : (a)  7, (b)  1                (c) 6                (d) 3

9.      How does the atomic radii change

(a)  On moving across the period in the periodic table?

(b) On moving down the group.Give reason.

ANS (a) On moving from left to right in a period of the periodic table, the atomic radius of elements decreases.

REASON:

-         (a) this is because the number of shell remain same but the nuclear charge increases.

-         Due to large positive charge on the nucleus, the electrons are pulled in more close to the nucleus and the size of the atom decreases.

(b) On moving down the group the atomic size increases. Although, the nuclear charge increases but due to the addition of a new energy shell the valence electrons become far away from nucleus. Hence, they are not held effectively by the nucleus thus increasing its size.

10.                        How does the non metallic character change

(a)  On moving across the period in the periodic table?

(b) On moving down the group in the periodic table?

ANS: (a) On moving from left to right in a period, the non metallic nature  (electronegative character ) increases

REASON:

-The non metals accept electrons and form negative ions, so non metals are electronegative in nature.

[-The greatest metallic character is found in the elements on the extreme left side of the period and the greatest non metallic character is found in elements on the extreme right side of a period.]

- due to increase in nuclear charge, (increase in no.of protons)the valence electrons are pulled in strongly by the nucleus and it becomes easier for the atoms to gain electrons.

(b)On going down the groups, non metallic character decreases.

REASON:

As we go down in a group of periodic table, one more electron shell is added to the atom and its size increases.

The attraction of nucleus for the incoming electron decreases, due to which atom cannot form negative ions and electronegative character decreases.

11.(a) What name is given to elements belonging to group 1 of the periodic table and why?

(c)  Name two elements for this group which can be easily cut with a knife?

ANS:( a) the elements belonging to group 1 are collectively known as ALKALI METALS. They are so called as they vigorously react with water to form highly soluble bases called alkalis. E.g. NaOH, KOH

(c)  sodium and Potassium

12. Chlorine has 2 isotopes Cl-35 and Cl-37. Would you place them in different slots because their atomic masses are different or would you place them in the same position because their chemical properties are same?

ANS:  according to Mendeleev’s periodic table Cl-35 and Cl-37 should be placed at different position as the basis of classification is increasing atomic masses but since their chemical properties are same , they should be placed in the same position in the periodic table.

13.Account the following:

(a)  Element in a group of the periodic table have similar chemical properties.

(b) Elements of group 18 are called zero valent.

ANS:   (a) the chemical properties of element are determined by its valence electron. So, in a group all the elements have same number of valence electron. Hence they exhibit similar chemical properties.

(c)  Because group 18 elements have their outermost shell complete.

14. Element M is in the first group of the periodic table. Write the formula of its oxide.

ANS:     M₂ O

15.  An atom has electronic configuration 2,8,2

(a)  What is the atomic number of the element.

(b) What is its valency?

(c)  To which element would it chemically similar and why: Be (4),  O(8)

ANS:(a)  12     (b)   2

(c)Be, because Be has two electron in its valence shell as in element mentioned.

16. Why is position of Hydrogen not justified in the periodic table.

ANS: Hydrogen with atomic number 1 shows properties similar to both alkali metals in group 1 and also to halogens in group 17. Thus, its position in group 1 with alkali metals is controversial.

17. An element M forms an oxide M₂O₃. It belongs to third period in the modern periodic table. Write the atomic number and valency of the metal.

ANS: the element is aluminium with atomic number 13 and valency 3.

18. Atomic number of few elements given below: (5 mks)

     10, 20, 7, 14

(a)  Identify these elements

(b) Identify group number of these elements

(c)  Period of the elements

(d) Electronic configuration of the elements

(e)  Determine the valency of these elements.

  ANS:   (a) 10 – Neon    20 – Calcium   7- nitrogen   14 – Silicon

(b)Neon – 18 group                        Calcium -2 group

 nitrogen – 3 group                         Silicon-14 group

19.How does the valency vary

(a)  On moving down the group?

(b) On moving across the period?

ANS: (a) On moving down the group, the valency of elements remains same in a particular group.

(c)  On moving across the period, the valency first increases from 1 to 4 and then decreases from 4 to zero.

20.Chlorine and bromine are kept in the same group in the periodic table. Why?

ANS: Cl and Br have been kept in the same group as they have same number of electrons and thus, show similar chemical properties.

21.There are 7 electrons in the outermost ‘L’ shell of an element . Predict the period and group in the periodic table this element belongs to.

ANS: name of the element is Fluorine

Group : 17        period: 2

NOTES ( NO WRITTEN WORK)

   There are 18 groups of elements divided into 9 main groups. They are 

I, II, III, IV, V, VI, VII, VIII and 0 groups. The groups I to VII has two sub

groups each called A – sub group and B – sub group. Group VIII has 3

rows of elements and 0 group has one row of elements.

    The A sub group elements are called normal elements.

   The B sub group elements are called transition elements.

    Lanthanides and Actinides are called inner transition elements.

    Group 1 (I A ) elements are called alkali metals

    Group 2 (II A) elements are called alkaline earth metals.

    Group 17 (VII A) elements are called halogens.

    Group 18 (0 group) are called noble gases.

     In a group all the elements have the same number of valence

electrons. Group I elements have 1 valence electron, Group II elements

have 2 valence electron, Group III elements have 3 valence electrons

etc.

   In a period all the elements contain the same number of shells.   

    Mendeleev classified elements in the increasing order of their atomic masses and similarities in their properties.

   The formulae of the oxides and hydrides formed by the elements was also the basis for the classification of the elements.

   Mendeleev’s periodic table has 6 horizontal rows called periods and 8 vertical rows called groups. The groups 1 to 7 had two sub groups called A sub group and B sub group. Group 8 had 3 rows of elements. Elements having similar properties were placed in the same groups. There are some spaces left vacant in the table to accommodate the elements to be discovered in future.

   Merits of Mendeleev’s periodic table :-

  i) Elements were classified on a more fundamental basis of their atomic masses and properties.

 ii) Spaces were left vacant to accommodate the elements to be discovered in  future.

iii) It could predict the properties of the elements which helped in the discovery of new elements.

iv) The inert gas elements discovered later could be placed in a separate group without  disturbing the table.

  Defects of Mendeleev’s periodic table :-

  i) Some elements are not arranged in the increasing order of their atomic masses. Co is placed before Ni,  Te is placed before I etc.

 ii) Position of hydrogen is not clear because it shows properties similar to metals as well as non metals.

iii) The position of isotopes of elements is not clear.

HINDI

notebook questions for chapter of reproduction

Q & A OF CARBON AND ITS COMPOUNDS

1.       Give the general formula of alkane, alkene, and alkyne.

Ans:   C_nH_2n+2,   C_nH_2n, C_nH_2n-2  respectively.

2.     Classify the following compounds as alkanes, alkenes and alkynes.

    C₂H_4,     C₃H₄, C₄H₈, C₅H₁₂,  C₅H₈,  C₃H₈, C₆H₆

ANS : alkanes – C₅H_12, ,  C₃H₈

Alkenes – C₂H₄, C₄H_8,

Alkynes – C₃H₄, C₅H₈

3.     Name the simplest hydrocarbon and give its formula.

Ans: Methane CH₄

4     4. Amongst C₂H₄  and C₂H₆ ,which is more reactive? Why?

Ans: Amongst C₂H₄  and C₂H₆, C₂H₄ is more reactive, as it is a unsaturated

Hydrocarbon and contains a reactive site (double bond) in it.

   5. Why carbon forms compounds by sharing of electrons and not by formation of ions?

Ans: carbon is tetravalent in nature. If it gains 4 electrons to form C^4- ions, then it will be difficult for 6 electrons to hold on to 10 electrons while formation of C⁴⁺ ions. i.e. loss of 4 electrons requires considerable amount of energy. Hence, it forms bond by sharing of electrons.

66.      Give reasons for the formation of large number of compounds by carbon.

Ans: carbon forms large number of compounds due to the following properties:

a.     CATENATION: due to this property, it can link to other carbon atoms to form straight chain, branched chain and ring structure.

b.     TETRAVALENCY: Due to its tetravalent nature, it can form bond with four atoms of carbon or some other elements.

  77. Give an important difference between saturated and unsaturated hydrocarbons.

Ans: In a saturated hydrocarbon all the carbon atoms in a compound are linked to other carbon atoms by single covalent bonds while in an unsaturated hydrocarbons, there is a presence of a double / triple covalent bond between the carbon atoms. E.g.ethane is a saturated hydrocarbon ethene is a unsaturated hydrocarbon.

 8.   What is structural isomerism? Give examples.

Ans;  The phenomenon of existence of compounds having same molecular formula but different structural formula is called structural isomerism, e.g. Butane has two structural isomers.

Iso butane and 2-methyl propane (IUPAC name)are the same.

NOTE: isomerism is possible only with hydrocarbons having 4 or more carbon atoms.

No isomerism is possible in methane, ethane and propane because they contain only one, two or three carbon atoms.

 9.    How many structural isomers are possible for pentane? Draw the structural formulae of all the possible isomers of pentane. Give their IUPAC names also.

Ans: the molecular formula of pentane is C₅H₁₂.

It has 5 carbon atoms

.i.  First write all the 5 C atoms in a straight chain. this is called as n-pentane.

ii. Next write  4 C atoms in a straight chain and 1 C atom in the side chain.

iii. Next write  3 C atoms in a straight chain and 2 C atom in two side     chain.

 10.                         Pure ethanoic acid is also called glacial acetic acid. Why?

ANS: Ethanoic acid has a low melting point of 290 K. thus, in cold weather ethanoic acid freezes to form glacier like crys tals. That is why Pure ethanoic acid is also called glacial acetic acid.

1

111.                      1 ml of glacial acetic acid and 1 ml of ethanol are mixed together in a test tube. Few deops of con. Sulphuric acid is added in the mixture and warmed in a water bath for 5 minutes.

a.     Name the resultant compound formed.

b.     Represent the above change by a chemical equation.

c.      What term is given to such reaction?

d.     What is the special characteristics of the compound formed?

e.     Give one important use of the compound formed.

ANS:

a.     The resulting compound formed is ester ( ethyl acetate). The IUPAC name this ester is ethyl ethanoate.

b.      

                                          Con. H₂SO₄                      

C₂H₅OH + CH₃COOH -------------------à CH₃COO C₂H₅   + H₂O

                                                               ∆   

c.      Esterification

d.     The compound formed has a sweet smell.

e.     Esters formed is used in making perfumes and as a flavouring agent. 

112.    What is saponification?

Ans: the alkaline electrolysis of esters (using alkali like sodium hydroxide) is known as saponification. This is because of the fact that this reaction is used  for the preparation of soap.

When an ester is heated with NaOH solution then the ester gets hydrolysed (breaks down) to form the parent alcohol and sodium salt of the  Carboxylic acid.

For e.g. when ethyl ethanoate ester is boiled with NaOH solution, then sodium ethanoate and ethanol are produced.

                                                       Heat

 CH₃COOC₂H₅   +  NaOH   ------------------à CH₃COONa       +       C₂H₅OH

 ethyl ethanoate                                           sodium ethanoate     Ethanol 

 (Ethyl acetate)

     13.. Write the structural formulae of  isomers of hexane.

14.                        Write the structural formulae of  isomers of butane. Also give their IUPAC names.

115.                        Give IUPAC names of the following compounds.

 ANS: PROPANONE

b.     Give IUPAC names of the following compound.

ANS: BUTANOIC ACID

c. 

  

ANS: PROPENE

d.

ANS : BROMO BUTANE

e. ETHANOL

 16.      Draw the structures of the following compounds.

a.   ETHANOIC ACID

b.  BROMO PENTANE

c.  BUTANON

d.   HEXANA

e.  BENZENE

a.     ANS: 

b . ANS: 

c.      ANS

d.     Ans

e.     Ans

 17.   Show the  bond formation in the following chemical compounds using electron dot structures. Indicate the type of bonding.

a. Ammonia

N – 2,5             H – 1 

 

TYPE OF BONDING: Covalent bonding

 b. METHANE

 

TYPE OF BONDING: Covalent bonding

 c.     CARBON DI OXIDE

 

 

TYPE OF BONDING: Covalent bonding

 d.    HYDROGEN CHLORIDE 

                                        

                                                              TYPE OF BONDING: Covalent bonding

 18.             Draw the electron dot structures of the following compounds. Also  give their molecular formula.

a.     ETHANE

₆C – 2, 4             ₁  H  - 1

Molecular formula  ; C₂H₆

119.  Why the compounds formed by carbon are exceptionally stable?

Ans: the stability of carbon compounds is attributed to the small size of carbon atom. Due to the small size of the carbon atom, the nucleus holds the shared pair of electron more effectively. Thus, making the bond stro

 20.    What do you mean by the term ‘homologous series’?

Ans: A series of compounds having same functional group similar chemical properties and the successive members of which differ by –CH₂ unit is called homologous series.

221.        List some important characteristics of ‘homologous series’.

Ans:  The  important characteristics of ‘homologous series’ are:

_a.               The adjacent members of homologous series differ by -CH₂  unit.

_b.               The molecular mass of any two successive member differ by 14 u.

c.       All the members of the series have same chemical properties and show regular gradation in their physical properties.

d.      All the members of the series have same functional group and can be represented by a general formula.

222.                        Define the term ‘functional group’.

Ans:  an atom or group of atoms that is the site of reactivity in the organic compound and largely determines the properties of an organic compound is called functional group.

223..                         What is hydrogenation? What is its industrial application?

Ans: The reaction that involves the addition of hydrogen across an unsaturated hydrocarbon (double/triple bond) in the presence of nickel catalyst is called hydrogenation.

Industrial application: Hydrogenation of vegetable oils in the presence of nickel catalyst converts them to Vanaspati ghee.

224..                        Two carbon compounds A and b have the molecular formula C₃H₈ and C₃H₆ respectively. Which one of the two is most likely to show addition reaction? Justify your answer. Explain with the help of chemical equation, how an addition reaction is useful in vegetable ghee industry.

Ans: unsaturated hydrocarbons undergo addition reaction. Since C₃H₆

Is an alkene i.e. an unsaturated hydrocarbon it would undergo addition reaction.

Unsaturated hydrocarbon       saturated fat

On adding hydrogen to an alkene in the presence of nickel catalyst , the addition of hydrogen takes place across the double bond and forms saturated fat called vanaspati ghee.

225..                       Explain the mechanism of the cleaning action of soaps.

Ans; A soap molecule is a sodium or potassium salt of long chain carboxylic acid. It consists of two parts i.e., a long hydrocarbon tail and a negatively charged head. The hydrocarbon tail is hydrophobic i.e. insoluble in water and repelled by water while the polar end is soluble in water and hydrophilic in nature.

   

          When soap is applied on a wet dirty surface, the polar end of the soap molecule dissolves in water while the non polar tail attaches it to dirt molecule, as dirt is non-polar in nature.

This results into the formation of spherical clusters called MICELLE. In the micelle the hydrophobic tails are in the interior of the cluster while the ionic ends are on the surface of cluster.

Due to ion-ion repulsion, the micelle stay in the solution as a colloid and don’t come together as precipitate. Thus, an emulsion is found which helps to dissolve dirt in water and it is finally washed with running water.

226.      Under what conditions can a saturated hydrocarbon produce  a sooty flame? Explain.

Ans: a saturated hydrocarbon produce  a sooty flame only when burnt in limited supply of oxygen. Due to the limited supply of oxygen, the incomplete combustion of the hydrocarbon takes place resulting in unburnt carbon producing sooty flame.

227.         Why gas/kerosene stoves used at home at holes at the bottom?

The bottom of the cooking vessels often gets blackened on heating. Give reason for blackening of cooking vessels.

Ans: . The gas/kerosene stoves are provided with air inlets so that oxygen rich mixture is burnt for the complete combustion and thus it produces a clean flame.

If the air holes of the gas stove gets blocked, then incomplete combustion of the fuel takes place due to limited supply of oxygen. This leads to the formation of soot that deposits on the vessel and thus get blackened.

228. a . Name the catalyst required for the hydrogenation of vegetable oils to vanaspati ghee.

b.     Name the product formed by the addition of hydrogen to ethane. Also write the chemical equation.

c.      Why do we prefer vegetable oils to animal fats for cooking purposes?

ANS:

a.     Nickel

b.     On addition of hydrogen to ethane, ethane is formed.

       H₂C =CH₂       +  H₂  ----------àH₃C – CH₃

          Ethene                                         ethane

c.      Vegetable oils are preferred to animal fats as they consist of unsaturated fatty acids, which are good for health.

229.  A carbon  compound ‘X ’ is an active ingredient of all alcoholic drinks and is a good solvent.

a.     Name the compound ‘X’.

b.     Write your observation when the compound ‘X’ is made to react with compound ‘Y’ which is used as a preservative for pickles.

c.      Write the chemical equation to represent the above change

.

ANS:

a.     Ethanol

b.     ‘Y’ is vinegar which is dilute solution of ethanoic acid. On adding ‘X’ to ‘Y’ a sweet smelling compound ester is formed.

c.                                                Con. H₂SO₄                     

C₂H₅OH + CH₃COOH -------------------à CH₃COO C₂H₅   + H₂O

                                                               ∆  

      

330.    Give the molecular  formula and IUPAC names of the following compounds.

a.     An alkyne containing 3 carbon atoms

b.     An alcohol containing 3 carbon atoms

c.      An aldehyde containing 3 carbon atoms

d.     Simplest ketone

e.     An  alcohol used in cough syrup

f.       A carboxylic acid used as a preservative

g.     A saturated hydrocarbon containing 5 carbon atoms

h.     A cyclehexane containing 5 carbon atoms

ANS:

a.     Propyne                        C₃H₄

b.     Pentanol                        C₅H₁₁OH

c.      Propanal                         C₂H₅CHO

d.     Propanone                      CH₃COCH₃

e.     Ethanol                            C₂H₅OH

f.       Ethanoic acid                   CH₃COOH

g.     Pentane                           C₅H₁₂

h.     Cyclopentane                C₅H₁₀