(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\\).

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’.

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

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.

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\\).

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}\\).

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

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.

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).\\)

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

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.

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\\)

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

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.

Subatomic Particles - Electron | Definition, Examples, Diagrams

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Discovery of electron by J.J. Thomson

In 1878 William Crooks carried out discharge tube experiments and discovered new radiations and called them cathode rays. Since these rays travel from the cathode towards anode. Later, J.J Thomson studied the characteristics of cathode rays and concluded that cathode rays are negatively charged particles, now called electrons. The name electron was given by Johnson Stoney.

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Properties of Cathode rays

1. Cathode rays travel in straight lines. That is why, cathode rays cast shadow of any solid object placed in their path. The path cathode rays travel is not affected by the position of the anode.

2. Cathode rays consist of matter particles, and posses energy by the virtue of its mass and velocity. Cathode rays set a paddle wheel into motion when it is placed in the path of these rays one the bladder of the paddle wheel.

3. Cathode rays consist of negatively charged particles. When cathode rays are subjected to an electrical field, these get deflected towards the positively charge plate(Anode).

4. Cathode rays heat the object only which they fall. The cathode ray particles possess kinetic energy. When these particles strike an object, a part of the kinetic energy is transferred to the object. The causes a rise in the temperature of the object.

5. Cathode rays cause green fluorescence on glass surface, i.e., the glass surface only which the cathode rays strike show a colored shine.

6. Cathode rays can penetrate through thin metallic sheets.

7. Cathode rays ionize the gases through which they travel.

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Electrical nature of matter

Matter is electrically neutral. It contains the equal number of protons and electrons that make the matter neutral. If there is a dis-balance in any one of them then the matter is positively or negatively charged depending on whether proton or electrons are more in number.

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Discovery of electrons by William Crookes

William Crookes in 1879, studied the conduction of electricity through a gases at low pressure. For this purpose, he took a discharge tube which is a long glass tube, about 60 cm long, sealed at both the ends and fitted with metal electrodes. It has a side tube fitted with a stop cock which can be connected to a vacuum pump to reduce the pressure of the gas inside to any desired value. These tubes are also now called as Crookes tube.

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Electron and its properties

Electron is the negative part of the matter. It is negatively charged. The properties of electrons are:

They are produced by the negative electrode, or cathode, in an evacuated tube, and travel towards the anode.
They travel in straight lines and cast sharp shadows.
They have energy and can do work.
They are deflected by electric and magnetic fields and have a negative charge.

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Millikan Oil's drop experiment

Millikan's oil drop experiment measured the charge of an electron. Before this experiment, existence of subatomic particles, was not universally accepted. Millikan's apparatus contained an electric field created between a parallel pair of metal plates, which were held apart by insulating material. Electrically charged oil droplets entered the electric field and were balanced between two plates by altering the field.

When the charged drops fell at a constant rate, the gravitational and electric forces on it were equal. Therefore, the charge on the oil drop was calculated using formula. Millikan found that the charge of a single electron was

1.6 \times 1 0^{- 19}

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Postulates of discovery of electrons

Postulates of Thomsons Model: an atom consists of a positively charged sphere, with electrons set within the sphere. An atom is electrically neutral as the positive and negative charges within it are equal.

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Charged particles

The charged particles are the particles which carries positive or negative charge on them. Ions could be positively or negatively charged, based on either they lose or gain the electrons in the outermost shell of their atom.

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Properties of Electrons

Once people got to know that subatomic particles exist, many scientists began to study electrical discharge in partially evacuated tubes, known as 'Cathode Ray Discharge Tubes'. Cathode rays move from negative electrode (cathode) to positive electrode (anode). Results of these experiments shed some light on physical properties of electrons which are summarized below:
1. Electrons are negatively charged particles and they travel from cathode to anode.
2. They are very light as compared to atom.
3. Nature of electrons do not depend on the material. They posses the same set of characteristics universally. Hence, electrons are basic constituent of all atoms.

Subatomic Particles - Electron

definition

Discovery of electron by J.J. Thomson

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Properties of Cathode rays

definition

Electrical nature of matter

definition

Discovery of electrons by William Crookes

definition

Electron and its properties

definition

Millikan Oil's drop experiment

definition

Postulates of discovery of electrons

definition

Charged particles

definition

Properties of Electrons

REVISE WITH CONCEPTS

Subatomic Particles - Protons

Subatomic Particles - Neutrons

Atomic Theory of Matter

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

definition

Discovery of electron by J.J. Thomson

definition

Properties of Cathode rays

definition

Electrical nature of matter

definition

Discovery of electrons by William Crookes

definition

Electron and its properties

definition

Millikan Oil's drop experiment

definition

Postulates of discovery of electrons

definition

Charged particles

definition

Properties of Electrons

REVISE WITH CONCEPTS

Subatomic Particles - Protons

Subatomic Particles - Neutrons

Atomic Theory of Matter

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: