Q: (i) Calculate the number of electrons which will together weighs one gram. (ii) Calculate the mass and charge of one mole of electrons.

The number of electrons which will weigh 1 g is \$\displaystyle \frac {10^{-3}}{9.11 \times 10^{-31}} = 1.098 \times 10^{27} \$ .Mass of one mole of electrons is \$\displaystyle 9.11 \times 10^{-31} \times 6.023 \times 10^{23}= 5.486 \times 10^{-7} \$kg.Charge of 1 mole of electrons is \$\displaystyle 1.602 \times 10^{-19} \times 6.023\times 10^{23} = 9.647\times 10^{4}\ C\$.

Q: Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?

The postulate of Dalton’s atomic theory resulting from the law of conservation of mass is ‘The relative number and kinds of atoms are constant in a given compound. Atoms cannot be created nor be destroyed in a chemical reaction’.

Q: An oil drop of 12 excess electrons is held stationary under a constant electric field of \$2.55\times10^{4} NC^{-1}\$ in Millikans oil drop experiment. The density of the oil is \$1.26\ g\ cm^{-3}\$. Estimate the radius of the drop. [g = \$9.8\ ms^{-2};\ \ \ \ e = \$1.60\$\times\,10^{-19}\$ C].

Excess electrons on an oil drop, \$n = 12\$Electric field intensity, \$E=2.55\times 10^4NC^{-1}\$Density of oil, \$\rho=1.26\,gm/cm^3=1.26\times 10^3kg/m^3\$Acceleration due to gravity, \$g=9.81\,m\,s^{-2}\$Charge on an electron, \$e=1.6\times 10^{-19}C\$Radius of the oil drop \$= r\$Force (F) due to electric field E is equal to the weight of the oil drop (W).\$F = W\$\$Eq = mg\$\$\displaystyle E_{ne}=\frac{4}{3}\pi r^3\times \rho \times g\$Where, \$q =\$ Net charge on the oil drop = ne\$m =\$ Mass of the oil drop \$=\$ Volume of the oil drop × Density of oil \$=\displaystyle \frac{4}{3}\pi r^3\times \rho\$\$\therefore r =\displaystyle \sqrt[3]{\frac{3\,E_{ne}}{4\pi\rho g}}\$\$\displaystyle =\sqrt[3]{\frac{3\times 2.55\times 10^4\times 12\times 1.6\times 10^{-19}}{4\times 3.14\times 1.26\times 10^3\times 9.81}}\$\$\displaystyle =\sqrt[3]{946.09\times 10^{-21}}\$\$=9.82\times 10^{-7}m\$\$=9.82\times 10^{-4}mm\$Therefore, the radius of the oil drop is \$9.82\times 10^{-4}mm\$.

Q: The increasing order for the values of \$e/m\$ (charge/mass) for electron (\$e\$), proton (\$p\$), neutron (\$n\$) and alpha particle (\$\alpha\$) is:

For neutron \$(n), \dfrac em=0\$For proton \$(p)= \dfrac em \times = \dfrac 11=1\$\$ For electron, \left( { e }^{ - } \right) , \dfrac em=\cfrac { 1 }{ 1/1837 } =1837\$For alpha particle \$\left( \alpha \right) , \dfrac em = \dfrac 24=0.5\$The increasing order for the values of \$\dfrac em\$ is \$n,α,p,e\$.Hence, the correct option is \$\text{D}\$.

Q: Which of the following statements about the electron is incorrect?

Explanation: Electrons have the following characteristics: 1. They are negatively charged particles. 2. The mass of the electron is \$200\$ times that of the neutron. The electron has a mass of \$9.1 \times {{10}^{-31}}\$ Kg and the neutron has a mass of \$1.67 \times {{10}^{-27}}\$ Kg. 3. They are the fundamental building blocks of all atoms. 4. Cathode rays are beams of electrons. Final Answer: The correct answer is option \$(B).\$

Question 1

(i) Calculate the number of electrons which will together weighs one gram. (ii) Calculate the mass and charge of one mole of electrons.

Accepted Answer

The number of electrons which will weigh 1 g is $\displaystyle \frac {10^{-3}}{9.11 \times 10^{-31}} = 1.098 \times 10^{27} $ .Mass of one mole of electrons is $\displaystyle 9.11 \times 10^{-31} \times 6.023 \times 10^{23}= 5.486 \times 10^{-7}   $kg.Charge of 1 mole of electrons is $\displaystyle 1.602 \times 10^{-19} \times 6.023\times 10^{23} = 9.647\times 10^{4}\ C$.

Question 2

Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?

Accepted Answer

The postulate of Dalton&#8217;s atomic theory resulting from the law of conservation of mass is &#8216;The relative number and kinds of atoms are constant in a given compound. Atoms cannot be created nor be destroyed in a chemical reaction&#8217;.

Question 3

Which of the following statements is not correct about the characteristics of cathode rays?

Accepted Answer

Characteristics of cathode rays are:(i) The cathode rays start from cathode and move towards the anode.(ii) These rays themselves are not visible but their behaviour can be observed with the help of phosphor materials such as $ZnS$.(iii) In the absence of electrical or magnetic field, these rays travel in straight lines.(iv) In the presence of electrical or magnetic field, the behaviour of cathode rays are similar to that expected from negatively charged particles, suggesting that the cathode rays consist of negatively charged particles, called electrons.(v) The characteristics of cathode rays (electrons) do not depend upon the material of electrodes and the nature of the gas present in the cathode ray tube.Option D provides a wrong statement.

Question 4

An oil drop of 12 excess electrons is held stationary under a constant electric field of $2.55\times10^{4} NC^{-1}$ in Millikans oil drop experiment. The density of the oil is $1.26\ g\ cm^{-3}$. Estimate the radius of the drop. [g = $9.8\ ms^{-2};\ \ \ \  e = $1.60$\times\,10^{-19}$ C].

Accepted Answer

Excess electrons on an oil drop, $n = 12$Electric field intensity, $E=2.55\times 10^4NC^{-1}$Density of oil, $\rho=1.26\,gm/cm^3=1.26\times 10^3kg/m^3$Acceleration due to gravity, $g=9.81\,m\,s^{-2}$Charge on an electron, $e=1.6\times 10^{-19}C$Radius of the oil drop $= r$Force (F) due to electric field E is equal to the weight of the oil drop (W).$F = W$$Eq = mg$$\displaystyle E_{ne}=\frac{4}{3}\pi r^3\times \rho \times g$Where, $q =$ Net charge on the oil drop = ne$m =$ Mass of the oil drop     $=$ Volume of the oil drop &#215; Density of oil     $=\displaystyle \frac{4}{3}\pi r^3\times \rho$$\therefore r =\displaystyle \sqrt[3]{\frac{3\,E_{ne}}{4\pi\rho g}}$$\displaystyle =\sqrt[3]{\frac{3\times 2.55\times 10^4\times 12\times 1.6\times 10^{-19}}{4\times 3.14\times 1.26\times 10^3\times 9.81}}$$\displaystyle =\sqrt[3]{946.09\times 10^{-21}}$$=9.82\times 10^{-7}m$$=9.82\times 10^{-4}mm$Therefore, the radius of the oil drop is $9.82\times 10^{-4}mm$.

Question 5

The increasing order for the values of $e/m$ (charge/mass) for electron ($e$), proton ($p$), neutron ($n$) and alpha particle ($\alpha$) is:

Accepted Answer

For neutron $(n), \dfrac em=0$For proton $(p)= \dfrac em \times = \dfrac 11=1$$ For electron, \left( { e }^{ - } \right) , \dfrac em=\cfrac { 1 }{ 1/1837 } =1837$For alpha particle $\left( \alpha  \right) , \dfrac em = \dfrac 24=0.5$The increasing order for the values of $\dfrac em$ is $n,&#945;,p,e$.Hence, the correct option is $\text{D}$.

Question 6

Which of the following is not a postulate of Dalton's atomic theory?

Accepted Answer

Postulates of Dalton's atomic theory:All matter consists of indivisible particles called atoms.Atoms of the same elements are similar in shape and mass but differ from the atoms of other elements.Atoms cannot be created or destroyed.Atoms of different elements may combine with each other in fixed, simple, whole-number ratios to form elements and compounds.The atom is the smallest unit of matter that can take part in a chemical reaction.'Atoms of a single element can have different masses' is not present in postulates of Dalton's atomic theory. It is in fact a limitation of Dalton's atomic theory. Hence, option D is the correct choice.

Question 7

Which of the following statements about the electron is incorrect?

Accepted Answer

Explanation:&#10;&#10;Electrons have the&#10;following characteristics:&#10;&#10;1. They are&#10;negatively charged particles.&#10;&#10;2. The mass of the&#10;electron is $200$ times that of the neutron.&#10;&#10;The electron has a&#10;mass of  $9.1 \times {{10}^{-31}}$ Kg&#10;and the neutron has a mass of $1.67 \times {{10}^{-27}}$ Kg.&#10;&#10;3. They are the&#10;fundamental building blocks of all atoms.&#10;&#10;4. Cathode rays&#10;are beams of electrons.&#10;&#10;Final Answer:&#10;&#10;The correct answer&#10;is option $(B).$

Question 8

On the basis of Thomson's model of an atom, explain how the atom is neutral as a whole?

Accepted Answer

Hint: Thomson atomic model is the first atomic model. It is also called the plum pudding model.Explanation : 1) According to the Thomson model, an atom consists of a positively charged sphere and the negatively charged electron are embedded in it.2) The negative and positive charges are equal in magnitude. So, the atom as a whole is electrically neutral.

Question 9

What are canal rays?

Accepted Answer

E. Goldstein in 1886 discovered the presence of new radiations in a gas discharge and called them canal rays. The beam of rays which travel in a direction away from anode towards cathode when gas is taken in a discharge tube is subjected to the action of high voltage under low pressure is known as canal rays. These rays were positively charged radiations which ultimately led to the discovery of another sub-atomic particle.Hence, the correct option is $A$

Question 10

Match column A (name of the Scientists) with column B (their contributions towards the understanding of the atomic structure).

Column A Column B
A. Ernest Rutherford 1. Indivisibility of atoms
B. J.J Thompson 2. Stationary orbits
C. Dalton 3. Concept of nucleus
D. Neils Bohr 4. Discovery of electrons
E. James Chadwick 5. Atomic number
F. E Goldstein 6. Neutron
G. Moseley 7. Canal rays

Accepted Answer

1. Rutherford did the scattering experiment and observed that some of the rays bounce back. He concluded that there is a mass in which positive charge is concentrated. This marks the discovery of nucleus.2. J.J Thomson discovered electrons by conducting cathode ray experiment.3. Dalton postulated that matter is made up of small particles caled atoms4. Neils bohr postulated that electrons revolve around the nucleus in fixed orbits. 5. James Chadwick discovered neutrons which has no charge.6. E Goldstein discovered protons by conducting canal rays experiment.7. Moseley did x ray experiment and concluded that the chemical properties are a periodic function of their atomic number.

R.A.Millikan experiment for discovery of the charge on electron

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REVISE WITH CONCEPTS

Subatomic Particles - Electron

QUICK SUMMARY WITH STORIES

Cathode Rays

(i) Calculate the number of electrons which will together weighs one gram.
(ii) Calculate the mass and charge of one mole of electrons.

Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?

Which of the following statements is not correct about the characteristics of cathode rays?

An oil drop of 12 excess electrons is held stationary under a constant electric field of $2.55 \times 1 0^{4} N C^{- 1}$ in Millikans oil drop experiment. The density of the oil is $1.26 g c m^{- 3}$ . Estimate the radius of the drop. [g = $9.8 m s^{- 2}; e =$ 1.60 $\times 1 0^{- 19}$ C].

The increasing order for the values of $e / m$ (charge/mass) for electron ( $e$ ), proton ( $p$ ), neutron ( $n$ ) and alpha particle ( $α$ ) is:

Which of the following is not a postulate of Dalton's atomic theory?

Which of the following statements about the electron is incorrect?

On the basis of Thomson's model of an atom, explain how the atom is neutral as a whole?

What are canal rays?

Column A	Column B
A. Ernest Rutherford	1. Indivisibility of atoms
B. J.J Thompson	2. Stationary orbits
C. Dalton	3. Concept of nucleus
D. Neils Bohr	4. Discovery of electrons
E. James Chadwick	5. Atomic number
F. E Goldstein	6. Neutron
G. Moseley	7. Canal rays

R.A.Millikan experiment for discovery of the charge on electron

Language

Rate

REVISE WITH CONCEPTS

Subatomic Particles - Electron

QUICK SUMMARY WITH STORIES

Cathode Rays

(i) Calculate the number of electrons which will together weighs one gram. (ii) Calculate the mass and charge of one mole of electrons.

Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?

Which of the following statements is not correct about the characteristics of cathode rays?

An oil drop of 12 excess electrons is held stationary under a constant electric field of 2.55×104NC−1 in Millikans oil drop experiment. The density of the oil is 1.26 g cm−3. Estimate the radius of the drop. [g = 9.8 ms−2; e=1.60×10−19 C].

The increasing order for the values of e/m (charge/mass) for electron (e), proton (p), neutron (n) and alpha particle (α) is:

Which of the following is not a postulate of Dalton's atomic theory?

Which of the following statements about the electron is incorrect?

On the basis of Thomson's model of an atom, explain how the atom is neutral as a whole?

What are canal rays?

(i) Calculate the number of electrons which will together weighs one gram.
(ii) Calculate the mass and charge of one mole of electrons.

An oil drop of 12 excess electrons is held stationary under a constant electric field of $2.55 \times 1 0^{4} N C^{- 1}$ in Millikans oil drop experiment. The density of the oil is $1.26 g c m^{- 3}$ . Estimate the radius of the drop. [g = $9.8 m s^{- 2}; e =$ 1.60 $\times 1 0^{- 19}$ C].

The increasing order for the values of $e / m$ (charge/mass) for electron ( $e$ ), proton ( $p$ ), neutron ( $n$ ) and alpha particle ( $α$ ) is: