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a) What is the charge and mass of the anode rays emitted when, hydrogen gas is enclosed in the discharge tube experiment? What is the name of these particles?

b) Do the anode rays always consist of protons whatever be the gas enclosed in the discharge tube? Explain.

a) In the case of hydrogen gas the anode rays consist of protons. A proton possesses one unit of positive charge and one unit of mass.

b) No, only in the case of hydrogen gas the anode rays consists of protons. In all other cases the anode rays consist of positive ions whose mass and charge vary according to the nature of the gas enclosed.

The anode rays are obtained when valence electrons are removed in the form of cathode rays from the atoms of the enclosed gas on passing high voltage of current. Since hydrogen atom consists of one electron and one proton, removal of this electron is in the form of cathode rays, and only protons remain and tube protons appear in the form of anode rays.

But in other cases, for example oxygen, the anode rays consist of positive ions. Oxygen atom consists of two valence electrons which are removed in the form of cathode rays. The positive ion formed, carry two units of positive charge and mass 16(8p + 8n).


a) What is the other name of X-rays?

b) How are x-rays produced? Why was this name given?

c) How are x-rays made tools in diagnostic purposes in the medical field?

a) X-rays are otherwise known as Roentgen rays, after their discoverer, Wilhelm K. Roentgen.

b) The rays obtained when, cathode rays strike an object like glass, are known as X-rays. Since the nature of X-rays was a mystery at the time of their discovery, these were referred to as X-rays. The letter, ‘X' is used as the name of an unknown property or quantity or a person.

c) X-rays are used by the doctors to find out the fractures of bones and also structural defects of other organs. This is because X-rays cast shadows of the bones etc on the photographic plates.


What is phosphorescence? How does it differ from fluorescence?

Phosphorescnece is a phenomenon in which certain substances like zinc salts, radium salts etc., glow, emitting visible light when they are irradiated either with X-rays or ultraviolet rays. The glow continues even after the source of light is cut off.

Fluorescent substances also emit light in the visible region when light falls on them. But they do not glow after the source of light is cut off where as phosphorescent substances continue emitting light under the same condition.


a) Who discovered the nuclear model of the atom?

b) Explain how Rutherford’s atomic structure cannot explain the stability of atom?

a) Rutherford was the first scientist to give the nuclear model of the atom. His descriptions that nucleus is present at the centre of the atom is unquestionable even today.

b) But Rutherford’s description that electrons move is different circular orbits, round the nucleus is not correct, as such, motion leads to the instability of the atom. This is because an electron moving in a circular orbit should accelerate. Further an electron, possessing a negative charge, when accelerated, should radiate energy and thus a moving electron goes on losing its energy and hence it is gradually attracted by the nucleus, consequently it falls into it, leading to instability.


Explain how Bohr’s atomic model explains the emission and absorption of radiation.

Bohr's atomic model states that electrons move in definite orbits possessing definite amount of energy. In other words the electrons in the first orbit or shell possess a definite energy, En1 while the electrons which move in second shell or orbit possess another definite energy, En2.

According to Bohr, an electron which moves from energy level En1, to energy level, En2, should absorb energy equal to En2 – En1 and it results in the absorption of energy and since absorption spectra.

When an electron jumps from higher energy level, En2 to lower energy level, En1 , it gives out or radiates energy equal to En2 – En1 , and gives emission spectra elements. Thus Bohr’s theory explains this spectra of the elements.


What is the charge and mass of a β-particle? From which part of the atom are β-particles emitted?

β - particles are nothing but highly energetic electrons. These rays are emitted straight from the nucleus.

β - rays are formed, during radioactivity by breaking of neutron into a proton and an electron. The proton is retained in the nucleus while electron is rejected in the form of β - rays.


a) The two elements, A and B have 17 electrons each in their atom. Element A has 35 nucleons while element B has 33 nucleons (nucleons are the total number of protons and neutrons in the nucleus). What is the relationship between these two elements? Explain.

b) The element A reacts with hydrogen in diffused light. Does the element B also react with hydrogen?

a) Elements A and B are known as isotopes, because both have same number of electrons which means same number of protons, i.e. same atomic number, but different mass number (nucleons).

b) Since isotopes possess same chemical properties, if A reacts with hydrogen in diffused light, B also gives the same reaction.


One isotope of carbon with atomic mass 12, occupies group 14 in the 2nd period in the long form periodic Table. Predict the position of another radioactive isotope of carbon with atomic mass 14?

The long form periodic table is based on the atomic number of the elements. Since the two isotopes of carbon possess the same atomic number 6, the position of radioactive carbon with atomic mass 14 is same as the other isotopes of carbon with the atomic mass 12.(i.e. 2nd Period Gr14).


a) What is the name given to the rays, traveling from cathode to anode?

b) Do the cathode rays always consist of electrons only, whatever be the gas enclosed in the discourage tube?

a) The rays, traveling from cathode to anode in the discharge tube, are called cathode rays.

b) Yes, cathode rays always consist of a stream of electrons whatever be the gas enclosed, because on passing high voltage of current through the rarefied gas, the electrons from the atom are knocked out and form cathode rays.


Why are electrons in the outermost shell known as valence electrons?

The outermost electrons in the atom are known as valence electrons because i) they participate in the chemical bonding during chemical reactions and ii) they determine the valence of that element.

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