Chemical Change and Chemical Bond

Question 1:

Complete the statement by filling the gaps using appropriate term from the terms given in the bracket.
(slow,  coloured,  arrow,  fast,  smell,  milky,  physical,  product,  chemical,  reactant,  covalent,  equality sign)

a. An................... is drawn in between the reactants and products while writing the equation for a chemical reation.

b. Rusting of iron is a............. chemical change.

c. The spoiling of food is a chemical change which is recognized from the generation of certain................ due to it.

d. A colourless solution of calcium hydroxide in a test tube turns..............on blowing in it through a  blow tube for some time.

e. The white particles of baking soda disappear when put in lemon juice. This means that it is a.....................change.

f. Oxygen is a....................... in respiration.

g. Sodium chloride  is....................compound while hydrogen chlorid is........................ compound.

h. Electron.............................. is complete in each hydrogen in a hydrogen molecule.

i. Chlorine (Cl₂) molecule is formed by..................... of electrons between two chlorine atoms.

ANSWER:

a. An arrow is drawn in between the reactants and products while writing the equation for a chemical reation.

b. Rusting of iron is a slow chemical change.

c. The spoiling of food is a chemical change which is recognized from the generation of certain  smell due to it.

d. A colourless solution of calcium hydroxide in a test tube turns  milky on blowing in it through a  blow tube for some time.

e. The white particles of baking soda disappear when put in lemon juice. This means that it is a chemical change.

f. Oxygen is a reactant  in respiration.

g. Sodium chloride  is ionic compound while hydrogen chloride is covalent compound.

h. Electron  duplet is complete in each hydrogen in a hydrogen molecule.

i. Chlorine (Cl₂) molecule is formed by sharing of electrons between two chlorine atoms.

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Question 2:

Explain by writing a word equation.

a. Respiration is a chemical change.

b. Hard water gets softened on mixing with a solutions of washing soda.

c. Lime stone powder disappears on adding to dilute hydrochloric acids.

d. Bubbles are seen on adding lemon juice to baking soda.

ANSWER:

a.Chemical change is a process in which a new substance is formed.

• Respiration is irreversible process
• During respiration, oxygen is convert into carbon-dioxide( a new substance is formed).
• During respiration, there is change in their chemical composition.
• During respiration, absorption and evolution of energy takes place.

These are characteristics of chemical reaction. Hence, respiration is a chemical reaction.

b.Sodium carbonate, Na₂CO₃, is also known as washing soda. It can remove temporary and permanent hardness from water. Sodium carbonate is soluble but calcium carbonate and magnesium carbonate are insoluble.
The carbonate ions from sodium carbonate reacts with calcium and magnesium ions in the water to produce insoluble precipitate.
For example:
Ca2+(aq) + Na2CO3 →CaCO3(s) +2Na+(aq)$C{a}^{2+}\left(aq\right) + N{a}_{2}C{O}_3 \to CaC{O}_3\left(s\right) +2N{a}^{+}\left(aq\right)$
The water is softened because it no longer contains dissolved calcium ions and magnesium ions.

c.Limestone is predominantly Calcium carbonate(CaCo₃). When calcium carbonate reacts with 10% solution of HCl. Then Calcium chloride is formed as a salt along with water and carbon dioxide gas (brisk effervescence).
2HCl + CaCO3 → CaCl2 + CO2 +H20$2HCl + CaC{O}_3 \to CaC{l}_2 + C{O}_2 +H_{2}0$
In this reaction, we add hydrogen ions (H⁺), which will react with the carbonate ion to form hydrogen carbonate HCO₃- ions, which are soluble in water and the limestone will dissolve.

d.Bubbles are seen on adding lemon juice to baking soda because lemon juice is citric acid and baking soda is sodium bicarbonate. On adding lemon juice in baking soda, we add acid in base then neutralization reaction is taking place resulting in the formation of salt ,water and brisk effervesence of carbon-dioxide.This CO₂ is released in the form of bubbles.
H3C6H5O7(aq) + 3 NaHCO3(aq) → Na3C6H5O7(aq) + 3 H2O(l) + 3 CO2(g)citric acid + baking soda→salt + water+carbon dioxide $$\begin{gathered} {\mathrm{H}}_3{\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{O}}_7\left(\mathrm{aq}\right) + 3 {\mathrm{NaHCO}}_3\left(\mathrm{aq}\right) \to {\mathrm{Na}}_3{\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{O}}_7\left(\mathrm{aq}\right) + 3 {\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) + 3 {\mathrm{CO}}_2\left(\mathrm{g}\right) \\ citric acid + baking soda\to salt + water+carbon dioxide \end{gathered}$$

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Question 3:

Match the pairs.

a. Photosynthesis	i. Tendency to lose electrons
b. Water	ii. Reactant in combustion process
c. Sodium chloride	iii. Chemical change
d. Dissolution of salt in water	iv. Covalent bond
e. Carbon	v. Ionic bond
f. Fluorine	vi. physical change
g. Magnesium	vii. Tendency to form anion

ANSWER:

 

a. Photosynthesis	i.    Chemical change
b. Water	ii.   Covalent bond
c. Sodium chloride	iii.  Ionic bond
d. Dissolution of salt in water	iv.   Physical change
e. Carbon	v.    Reactant in combustion process
f.  Fluorine	vi.  Tendency to form anion
g. Magnesium	vii. Tendency to lose electrons

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Question 4:

Show with the heip of diagram of electronic configuration how the following compound are formed from the constituent atoms.
a. Sodium chloride  
b. Potassium fluoride
c.Water  
d. Hydrogen chloride

ANSWER:

a. Sodium chloride :

Step 1 : Write the symbols of the radicals.
                           Na                         Cl
Step 2 : Write the valency below the respective radical.
                           Na                         Cl
                            1                           1

Step 3 : Cross-multiply symbols of radicals with their respective valency.

                         
Step 4 : Write down the chemical formula of the compound.
        
              NaCl

b. Potassium fluoride :

Step 1 : Write the symbols of the radicals.
                           K                            F
Step 2 : Write the valency below the respective radical.
                           K                            F
                            1                           1
Step 3 : Cross-multiply symbols of radicals with their respective valency.

                         
Step 4 : Write down the chemical formula of the compound.
        
              KF

c.Water :

Step 1 : Write the symbols of the radicals.
                           H                      O
Step 2 : Write the valency below the respective radical.
                           H                      O
                            1                      2
Step 3 : Cross-multiply symbols of radicals with their respective valency.

                         
Step 4 : Write down the chemical formula of the compound.
        
              H₂O

d. Hydrogen chloride :

Step 1 : Write the symbols of the radicals.
                           H                      Cl
Step 2 : Write the valency below the respective radical.
                           H                       Cl
                            1                       1
Step 3 : Cross-multiply symbols of radicals with their respective valency.

                         
Step 4 : Write down the chemical formula of the compound.
        
              HCl

Std.8 Cell and Cell Organelles

Who am I ?
A. I am ATP producing factory ?
B. I am single layered. but maintain cellular osmotic pressure.
C. I support the cell, but I am not cell wall. I have a body resembling net.
D. I am chemical factory of the cell.
E. Leaves are green because of me.
 

ANSWER:

Ans 1 a. Mitochondria
b. Cell wall
c. Cell membrane
d. Mitochondria
e. Chloropyhll

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Question 2:

What would have happend ? If.........
A. RBCs had mitochondria.
B. There had been no differences between mitochondria and plastids.
C. Genes had been absent on the chromosomes.
D. Plasma membrane had not been selectively permeable.
E. Plants lacked anthocyanin.
 

ANSWER:

a. RBC's are a type of cells which are found in blood. Their function is to carry oxygen to different cells and tissues of the body. They do not contain mitochondria for two purposes:
firstly, it saves the space in the red blood cells and so more of oxygen can bind to it
secondly, it prevents the use of oxygen which is bounded to RBC's.

If mitochondria would have been present in RBC's, the oxygen which is carried by them will be used up by the RBC's. Thus, there will be less or no oxygen left which can be transported to the cells and tissues.

b. Mitochondria and plastids are two different structures and they have specific functions. Mitochondria are found in both plants and animals whereas plastids are found only in plants. The main role of mitochnodria is to provide energy to the cells for carrying out their various functions. If, there would have been no difference between mitochondria and plastids, there would have been no structure which would provide energy and thus all the processes which take place in the cell would cease.

c. Genes are hereditary structures which contain the information which is passed on from one generation to another. They are required for the transmission of information from one generation to another. They are responsible for the characteristics of all the living organisms. They store the information for the various processes which occur in all the living organisms.

d. Plasma membrane is selectively permeable which means it allows the entry or exit of selective materials inside and outside the cell. In its absence, the regulated movement of substances in  and out of the cell will be affected.

e. Anthocyanin is a pigment which is present in plants and imparts them purplish colour. In the absence of this pigment, the structures which usually have purple colour due to its presence would appear colourless.

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Question 3:

Who is odd man among us ? Give reason.
a. Nucleolus, mitochondria, plastids, endoplasmic reticulum
b. DNA. Ribosomes, Chlorophyll

ANSWER:

a. Plastids are the odd one out because they are organelles which are found only in plant cells. Rest all the organelles are found in both plants and animals.
b. Chlorophyll is the odd one out beacuse it is a type of pigment which is found in plants only. DNA and ribosomes are found in both plants and animals.

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Question 4:

Give functions.
A. Plasma membrane
B. Cytoplasm
C. Lysosome
D. Vacuole
E. Nucleus
 

ANSWER:

a. Functions of the plasma membrane:

• It gives shape and support to the cell.
• It acts as a mechanical barrier to protect the internal contents of the cell.
• It separates the contents of the cell from its surrounding medium. 
• It performs physical activities such as diffusion and osmosis. 

b. Functions of cytoplasm:

• It is the medium for all cellular chemical reactions.
• It is a medium in which the organelles remain suspended.
• It helps in the movement of the different cellular elements. 

c. Functions of lysosomes:

• Lysosomes destroy foreign materials that enter the cell.
• Dead and worn-out organelles are removed by lysosomes.
• Cells are autolysed by lysosomes, and their contents are released within the cell.

d. Functions of vacuoles:

• The main function of vacuoles is to store food in a cell.
• They also help in storing and expelling wastes and toxic by products of metabolic reactions.
• They help in maintaining the turgidity and rigidity of a cell.

e. Functions of nucleus:

• It is the control centre of a cell as it controls all the activities of the cell.
• It also contains gene-containing chromosomes which are the units of inheritance in an organism.

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Question 5:

Who gives me the colour? (Select the correct option)

a. Red tomato	1.Chlorophyll
b. Green leaf	2. Carotene
c. Carrot	3. Anthocyanin
d. Violet	4. Lycopene

ANSWER:

a. Red tomato	4. Lycopene
b. Green leaf	1.Chlorophyll
c. Carrot	2. Carotene
d. Violet	3. Anthocyanin

Composition of matter

Question 1:

Choose the appropriate option and rewrite the following statements.
A. The intermolecular force is _______ in the paricles of solid.
i. Minimum    ii. Moderate    iii.maximum    iv.indefinite.

B. Solids retain their voume even when external pressure is applied. This property is called__________
i. plasticity    ii. Incompressibility    iii. fluidity    iv. elasticity

C. Matter is classified into the types mixture, compound and element by applying the criterion______________
i. states of matter    ii Phases of matters    iii chemical compositions of matter    iv all of these

D. Matter that contain two or more constituent substances is called__________
i. mixture    ii. compound    iii. element    iv. metalloid

E. Milk is an example of type of matter called __________
i. solution    ii. homogeneous mixture    iii heterogeneous mixture    iv. suspension

F. Water, mercury and bromine are similar o each other, because three are
i. liquids    ii. compounds     iii. nonmetals    iv. elements.

G. valency of carbon is 4 and that of oxygen is 2. From this, we understand that there are _______ chemical bond/bonds between the carbon atom and one oxygen atom in the compound-carbon dioxide.
i. 1    ii. 2    iii. 3     iv. 4 

ANSWER:

A. The intermolecular force is  maximum in the paricles of solid.
i. Minimum    ii. Moderate    iii.maximum    iv.indefinite.

B. Solids retain their voume even when external pressure is applied. This property is called incompressibility.
i. plasticity    ii. Incompressibility    iii. fluidity    iv. elasticity

C. Matter is classified into the types mixture, compound and element by applying the criterion states of matter.
i. states of matter    ii Phases of matters    iii chemical compositions of matter    iv all of these

D. Matter that contain two or more constituent substances is called compound.
i. mixture    ii. compound    iii. element    iv. metalloid

E. Milk is an example of type of matter called homogeneous mixture.
i. solution    ii. homogeneous mixture    iii heterogeneous mixture    iv. suspension

F. Water, mercury and bromine are similar to each other, because three are liquids.
i. liquids    ii. compounds     iii. nonmetals    iv. elements.

G. valency of carbon is 4 and that of oxygen is 2. From this, we understand that there are 2 chemical bond/bonds between the carbon atom and one oxygen atom in the compound carbon dioxide.
i. 1    ii. 2    iii. 3     iv. 4 

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Question 2:

Identify the odd term out and explain
A. Gold, silver, copper, brass
B.Hydrogen, hydrogen peroxide, carbon dioxide, water vapour.
C.Milk, lemon juice, carbon, steel.
D.water, mercury, bromine, petrol.
E.sugar, slat, baking soda, blue vitrol.
F.Hydrogen, sodium, potassium, carbon.

ANSWER:

a.Brass is odd one out because it is an alloy and gold, silver, copper are element.
b.Hydrogen is odd one out because it is an element and others are compound.
c.Carbon is odd one out because it is an element and others are mixture of various elements.
d.Water is odd one out because it is universal solvent and rest are not universal solvent.
e.Baking soda is odd one out because it is a mixture of various elements and others are compound.
f.Carbon is odd one out because it has 4 valence electrons and others have 1 valence electron.

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Question 3:

Answer the following questions.
A.Plants synthesize glucose in sunlight with the help of chlorophyll from carbon dioxide and water and give away oxygen. identify the four compounds in this process and name their types.

B. In one sample of brass, the following ingredients were found : copper (70%) and zinc (30%).  Identify the solvent, solute and solution from these.

C. Sea water tastes salty due to the dissolved salt. the salinity (the proportion of salts in water) of some water bodies Lonar lake - 7.9 %, Pacific Ocean 3.5%, Mediterranean sea- 3.8%, Dead sea- 33.7%. Explain two characteristics of mixture from the above information.

ANSWER:

a.Photosynthesis is a chemical process through which plants, some bacteria and algae, produce glucose and oxygen from carbon dioxide and water, using only light as a source of energy, which is absorbed by chlorophyll.
6CO2 + 6H2O → C6H12O6 + 6O2$6{\mathrm{CO}}_2 + 6{\mathrm{H}}_2\mathrm{O} \to {\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6 + 6{\mathrm{O}}_2$
Four substances in this process are as follows:
1.Carbon dioxide = organic compound
2.Water = organic compound
3.Glucose = organic compound
4.Chlorophyll = organo-metallic compound or complex compound

b.Brass is an alloy made primarily of copper, usually with zinc.Brass as a solid solution consisting of zinc and other metals as solute dissolved in copper taken as solvent. So that, the brass meets all the criteria of a solution.

c.Characteristics of mixtures from above information are:
1.Constituent substances of a mixture are two or more elements or compounds.
2.The proportion of constituent substances in a mixture can be variable.
3.The properties of constituent substances are retained in the mixture.

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Question 4:

Give two examples each
A. Liquid element
B. Gaseous element
C. Solid element
D.Homogeneous mixture
E.Colloid
F.Organic compound
G.Complex compound
H.Inorganic compound
I.Metalloid
J.Element with valency 1
K.Element with valency 2

ANSWER:

a.Liquid element = mercury, bromine
b.Gaseous element = oxygen, nitrogen, hydrogen
c.Solid element = sodium, carbon, aluminium
d.Homogeneous mixture = sugar in water, corn oil, blood plasma
e.Colloid = mayonnaise, milk, butter, gelatin, jelly, muddy water
f.Organic compound = proteins, glucose, urea, carbohydrates
g.Complex compound = chlorophyll, hemoglobin, cyanocobalamine
h.Inorganic compound = limestone, rust, common salt
i.Metalloid = silicon, germanium
j.Element with valency 1 = sodium, potassium, chlorine
k.Element with valency 2 = magnesium, calcium

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Question 5:

Write the names and symbols of the constituent eleements and identify their valencies from the molecular formulae given below.
KCl,   HBr,   MgBr₂,   K₂O,  NaH,   CaCl_2,  CCl₄,  HI,   H₂S, Na₂S,   FeS,   BaCl₂

ANSWER:

Compounds	Name of compounds	Symbol of constituent elements	Valency of constituent elements
KCl	Potassium chloride	K, Cl	K = 1, Cl = 1
HBr	Hydrogen bromide	K, Br	K = 1, Br = 1
MgBr2	Magnesium bromide	Mg, Br	Mg = 2, Br = 1
K2O	Potassium oxide	K, O	K = 1, O = 2
NaH	Sodium hydride	Na, H	Na = 1, H = 1
CaCl2	Calcium chloride	Ca, Cl	Ca = 2, Cl = 1
CCl4	Carbon tetrachloride	C, Cl	C = 4, Cl = 1
HI	Hydrogen iodide	H, I	H = 1, I = 1
H2S	Hydrogen sulphide	H, S	H = 1, S = 2
Na2S	Sodium sulphide	Na, S	Na = 1, S = 2
FeS	Iron (II) Sulfide	Fe, S	F = 2, S = 2
BaCl2	Barium chloride	Ba, Cl	B = 2, Cl = 1

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Question 6:

Chemical composition of some matter is given in the following table. Identify the main type of matter from their.

Name of matter	Chemical composition	Main type of matter
Sea water	H2O + NaCl + MgCl2$H_{2}O + NaCl + MgC{l}_2$
Distilled water	H2O$H_{2}O$
Hydrogen gas filled  in a ballon	H2$H_2$
The gas in LPG cylinder	C4H10 + C3H8$C_4{H}_{10} + C_3{H}_8$
Baking soda	NaHCO3$NaHC{O}_3$
Pure gold	Au$Au$
The gas in oxygen cylinder	O2
Bronze	Cu + Sn
Diamond	C
Heated white powder of blue vitroi	CuSO4
Lime stone	CaCO3
Dilute hydrochloric acid	HCL+ H2O

ANSWER:

 

Name of matter	Chemical composition	Main type of matter
Sea water	H2O + NaCl + MgCl2$H_{2}O + NaCl + MgC{l}_2$	mixture
Distilled water	H2O$H_{2}O$	compound
Hydrogen gas filled  in a ballon	H2$H_2$	element(molecule)
The gas in LPG cylinder	C4H10 + C3H8$C_4{H}_{10} + C_3{H}_8$	mixture
Baking soda	NaHCO3$NaHC{O}_3$	mixture
Pure gold	Au$Au$	element
The gas in oxygen cylinder	C4H10 + C3H8$C_4{H}_{10} + C_3{H}_8$	element(molecule)
Bronze	Cu + Sn	mixture
Diamond	C$C$	element(allotrope)
Heated white powder of blue vitroi	CuSO4${\mathrm{CuSO}}_4$	compound
Lime stone	CaCO3$CaC{O}_3$	compound
Dilute hydrochloric acid	HCL+ H2O$\mathrm{HCL}+ {\mathrm{H}}_2\mathrm{O}$	compound

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Question 7:

Write scientific reason.
A. Hydrogen is combustible, oxygen helps combustion, but water helps to extinguish fire.
B. Constituent substances of a colloid cannot be separated by ordinary filtration.
C. Lemon sherbat has sweet, sour and salty taste and it can be poured in a glass.
D. A solid matter has the properties of definite shape and volume.

ANSWER:

a.Water is made up of two elements, that's hydrogen and oxygen. Hydrogen is flammable, but oxygen is not. Flammability is the ability of a combustible material with an adequate supply of oxygen (or another oxidiser) to sustain enough heat energy to keep a fire going after it has been ignited. Though water is made up of two atoms of hydrogen and one atom of oxygen by forming an ionic compound, it does not possess the characteristics of them because a compound does not have the properties of its constituent elements. Therefore, water has its own properties, which helps to extinguish fire.

b.Constituent substances of a colloid cannot be separated by ordinary filtration because the size of the particles in a colloids(or colloidal solution) is bigger than those in a true solution but smaller than those in suspension.It is in between 1nm to 100nm in diameter. The size of ordinary filter paper is more than 100nm due to which colloidal particles are passed through the pores of a filter paper. Due to which, we prefer to use ultrafilter paper so that, filteration of colloidal particles take place easily.


c.Lemon sherbat has sweet, sour and salty taste and it can be poured in a glass because sour taste indicates presence of an acid and if acid is poured in a vessel made up of metal, then acid reacts with metal and makes it poisonous in nature.So we prefer to take vessel made up of glass material.

d.A solid matter has the properties of definite shape and volume because of the following reasons:
1)Intermolecular force of attraction between the particles of matter is very strong.
2)Internuclear space between the particles of matter is negligible.
3)Particles of matter are very close to each other that they only vibrate at their fixed position.
 

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Question 8:

Deduce the molecular formulae of the compound obtained from the following pairs of elements by the cross multiplication method.
A. C (Valency 4) & Cl (Valency 1)
B. N (Valency 3) & H (Valency 1)
C. C (Valency 4) & O (Valency 2)
D. Ca (Valency 2) & O  (Valency 2)

ANSWER:

a. C (Valency 4) & Cl (Valency 1) :
Step 1 : Write the symbols of the radicals.
                           C                       Cl
Step 2 : Write the valency below the respective radical.
                           C                        Cl
                            4                        1
Step 3 : Cross-multiply symbols of radicals with their respective valency.
                            
Step 4 : Write down the chemical formula of the compound.
                            CCl₄


b. N (Valency 3) & H (Valency 1)
Step 1 : Write the symbols of the radicals.
                           N                      H
Step 2 : Write the valency below the respective radical.
                           N                      H
                            3                      1
Step 3 : Cross-multiply symbols of radicals with their respective valency.
                          
Step 4 : Write down the chemical formula of the compound.
                           NH₃


C. C (Valency 4) & O (Valency 2)
Step 1 : Write the symbols of the radicals.
                           C                       O
Step 2 : Write the valency below the respective radical.
                           C                        O
                            4                        2
Step 3 : Cross-multiply symbols of radicals with their respective valency.
                           
Step 4 : Write down the chemical formula of the compound.
                           CO₂


D. Ca (Valency 2) & O  (Valency 2)
Step 1 : Write the symbols of the radicals.
                           Ca                     O
Step 2 : Write the valency below the respective radical.
                           Ca                       O
                            2                        2
Step 3 : Cross-multiply symbols of radicals with their respective valency.
                          
Step 4 : Write down the chemical formula of the compound.
                          CaO

Inside the atom (std.8)

Question 1:

Answer the following
A. Whati is the difference in the atomic models of Thomson and Rutherford ?
B. What is meant by valency of an element ? what is the relationship between the number of valence electron and valency ?
C. What is meant by atomic mass number ? Explain how the atomic number and mass number of carbon are 6 and 12 respectively.
D. what is meant by subatomic particle ? give brief information of three subatomic particles with refrence to electrical charge, mass and location.

ANSWER:

a. Difference between Thomson and Rutherford Theory are as follows :
 

Thomson Theory	Rutherford Theory
States that electron are embedded in a positively charged solid material which is spherical in shape	States that an atom is composed of an atomic nucleus around which electrons are revolving in an orbit
Does not give any detail about the atomic nucleus	Explains about the atomic nucleus
States that electrons are uniformally distributed in an atom	States that electrons are located around a central solid material
Indicates that atom is spherical in shape	Indicates that an atom has a central solid core called as nucleus surrounded by the electrons
Does not give any idea about constituents of nucleus	States that nucleus is composed of protons and neutrons

b. Valency of an element : It is the number of electrons of an atom of the element uses to combine with atoms of other elements.
It is the combining power of an atom of the element.
Valency of an atom is determined by its electronic configuration.
It gives idea about the number of electrons loss or gain in order to achieve the nearest noble gas configuration.
For example: Na(11) = 2,8,1 So, its valency is 1
                      Cl(17) = 2,8,7 So, its valency is also 1

Number of valence electron : It is defined as the number of electrons present in the outermost shell of an atom.
It is not necessary that all the valence electrons take part in bonding.
For example: Na(11) = 2,8,1 So, its number of valence electron is 1
                      Cl(17) = 2,8,7 So its number of valence electron is 7

It can be seen that valency of an element is related to number of valence electrons in that atom.


c.Atomic Mass Number : It is the sum of total number of protons and neutrons present in a nucleus.
Atomic mass number = number of protons + number of neutrons.
Atomic number = number of protons = number of electrons. It is denoted by Z.
Mass number = number of protons + number of neutrons. It is denoted by A.
For example : Carbon atom its, Number of proton = 6
                           Number of neutrons = 6
                           Number of electron = 6
                           Atomic number(Z) = number of protons = number of electrons = 6.
                           Mass number(A) = number of proton + number of neutrons = 6 + 6 =12.
 
d.Subatomic particles : A subatomic particle is a structural and functional unit of the matter. That means all the matters are made up of these fundamental particles. According to modern atomic theory, an atom has a nucleus, which is present in its center or core. These nucleus contain subatomic particles like protons and neutrons.
Difference between subatomic particles are as follows :

Electron
1. Electrons are present outside the nucleus of an atom.
2. Electrons are negatively charged that is (1.6 × 10−19$1.6 \times {10}^{-19}$coulomb).
3. The mass of an electron is considered to negligible. It is 1800  times less than that of a hydrogen
4.Relative mass = 1/ 1840 times hydrogen
5. It revolves around the nucleus in the discrete orbit.

Proton
1. Protons are present in the nucleus of an atom.
2. Protons are positively charged that is (1.6 × 10−19$1.6 \times {10}^{-19}$coulomb).
3. The mass of a proton is approximately 1u(1Dalton) that is (1u = 1.66 × 10−27 g$1u = 1.66 \times {10}^{-27 }g$).
4. They are closely bound in the nucleus.

Neutron
1. Neutrons are present in the nucleus of an atom.
2. Neutrons are neutral.There is no charge.
3. The mass of a neutron is nearly equal to the mass of a proton that is 1u(1Dalton) that is (1u = 1.66 × 10−27 g$1u = 1.66 \times {10}^{-27 }g$).
4. They are closely bound in the nucleus.

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Question 2:

Give secientific reasons.
A. All the mass of an atom is concenrated in the nucleus.
B. Atom is electrically neutral.
C. Atomic mass number is a whole number.
D. Atoms are stable though negatively charged electron are revolving within it. 

ANSWER:

a. All the mass of an atom is concentrated in the nucleus because atom contains three subatomic particles like electron, proton and neutron.Out of which, nucleus present at the centre of an atom contains two subatomic particles that's protons and neutrons and the mass of nucleus is the sum of mass of protons and neutrons located at the centre of an atom.

b.Atom is electrically neutral because in an atom electrons and protons carry charges and each atom has equal numbers of protons (positively charged) and electrons (negatively charged).

c.Atomic mass number is a whole number because it is the sum of numbers of protons and numbers of neutrons present in an atom.Which is present in the form of integers.

d.Atoms are stables though negatively charged electrons are revolving within it because each atom contains equal numbers of protons and electrons. So, charge on negatively charged electrons are balanced by charge on positively charged proton. Therefore, atom is electrically neutral and stable. 

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Question 3:

Define the following forms
A. Atom 
B. Isotope
C. Atomic number
D. Atomic mass number
E. Moderator in nuclear reactor

ANSWER:

a. An atom is defined as  the structural and functional unit of a matter. The term "atom" comes from the Greek word which means indivisible, because atoms are the smallest things in the universe and could not be divided. atoms are made up of three subatomic particles like protons, neutrons and electrons.

b.Isotopes : Isotopes are atoms that have same atomic number but different mass number. Isotopes have same numbers of protons but different numbers of neutrons.
These are some common examples of isotopes: 3
2He, 4
2He, 12
6C, 14
6C, 235
92U, 239
92U, 289.


c.Atomic number: The number of protons in the nucleus of an atom, which is characteristic of a chemical element and determines its place in the periodic table. Atomic number is also equal to numbers of electrons in an atom.
For example :
Atomic number of carbon = 6
Atomic number of nitrogen = 7
Atomic number of oxygen = 8
Atomic number of magnesium = 12


d.Atomic Mass Number : It is the sum of total number of protons and neutrons present in a nucleus.
atomic mass number = number of protons + number of neutrons.
Atomic number = number of protons = number of electrons.It is denoted by Z.
Mass number = number of protons + number of neutrons. It is denoted by A.
For example : Carbon atom its, Number of proton = 6
                           Number of neutrons = 6
                           Number of electron = 6
                           Atomic number (Z) = number of protons = number of electrons = 6
                           Mass number (A) = number of proton + number of neutrons = 6 + 6 =12

e.Moderator in nuclear reactor: Moderator of a nuclear reactor is a substance that slows down the speed of neutrons. In traditional nuclear reactors, the moderator is the same thing as that of coolant like water.

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Question 4:

Draw a neat lablled diagram
A. Ruthrford's scattering experiment
B. Thomson's atomic model
C. Diagramatic sketch of electronic configurations of magnesium  (Atomic number 12)
D. Diagramatic sketeh of electronic configuration of Argon (Atomic number 18)

ANSWER:

a. Rutherford's scattering experiment :

b. Thomson's atomic model

c. Diagramatic sketch of electronic configurations of magnesium  (Atomic number 12) :

 

d. Diagramatic sketeh of electronic configuration of Argon (Atomic number 18) :

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Question 5:

Fill in the blanks.
A. Electron, proton, neutron are the types of _________ in an atom.
B. An electron carries a _________charge.
C. The electron shell _____________ is nearest to the nucleus.
D. The electronic configuration magnesium is 2,  8,  2. From  this it is understood that the valence shell of magnesium is_____________
E. The valency of hydrogen is 'one as per the molecular formula H₂O . Therefore valency of 'Fe' turns out to be ______________ as per the formula Fe₂O₃. 

ANSWER:

a. Electron, proton, neutron are the types of subatomic particles in an atom.
b. An electron carries a negative charge.
c. The electron shell K is nearest to the nucleus.
d. The electronic configuration magnesium is 2,  8,  2. From  this it is understood that the valence shell of magnesium is M shell.
e. The valency of hydrogen is 'one as per the molecular formula H₂O . Therefore valency of 'Fe' turns out to be three as per the formula Fe₂O₃. 

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Question 6:

Match the pairs.

Group 'A'	Group 'B'
a. Proton	i.Negatively charged
b.Electron	2.Neutral
c.Neutron	3.Positively charged

ANSWER:

Match the pairs:

Group 'A'	Group 'B'
a.Proton	1.Positively charged
b.Electron	2.Negatively charged
c.Neutron	3.Neutral

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