Important Question Answers Chemistry-11 CH 5: Atomic Structure

Important Question Answers Chemistry-11 CH 5: Atomic Structure

Important Question Answers Chemistry-11 CH 5: Atomic Structure

Q.1 Write postulates of Dalton’s atomic theory.

Ans: The main postulates of Dalton’s atomic theory are:

  • All matter is made up of extremely small, indivisible particles called atoms.
  • Atoms of one element differ from atoms of all others elements in mass and chemical properties but all the atoms of a particular element have identical properties.
  • Atom is the smallest particle that can take part in a a chemical reaction.
  • Atoms of different element may combine with each other in a fixed simple whole number ratio ot form compounds.
  • Atoms can neither be created not destroyed during chemical reactions.

Q2. What are molecular ions? How are they generated?

Ans: Molecular ions are formed when a molecule loss or gain electrons. For example, CH4+ ,

Q3. Why we use relative atomic mass unit?

Ans: It is mass of an atom of an element relative to mass of an atom of carbon taken as 12. Atoms have very small sizes and masses. We don’t have any balance ot weight chuch small masses. So we find mass by comparing with the mass of carbon-12. That is why we uses relative atomic mass unit.

1 amu = 1.661 x 10 -24g = 1.661 x 10-27kg

Q3. Atomic masses may be in fractions. Justify.

Ans: Most of the elements contain isotopes. Atomic masses maybe in fractions because atomic masses are average masses of isotopes proportional to their relatives abundance. For example, Neon has three isotopes of atomic masses 20, 21, 22 with relatives abundance as 90.92%, 0.26% and 8.32% the relqative atomic mass of neon mass of all the three isotopes and there is no neon atoms with ths atoms mass.

Q.4 No individual neon atom is the sample of element has mass of 20.18 a.m.u. Explain with reason.
Ans: Neon has three isotopes of atoms masses 20, 21, 22 with relative abundance as 90.92% , 0.26%  and 8.82% the relative atoms mass of neon acomes out to be 20.18 a.m.u. So 20.18 a.m.us is th eaveratea tomic mas s ofll the three isotopes and there is no noen atom with this atomic mass.

Q5. Why isotopes have same chemeical and defferent physical properties?
Ans: Physical properties depend upon the atomc masses. As isopopes tahve different atoms masses so they have different physical properties. Chemical properties depend upon the atomic numbers. As isotopes have same atomic number, so they hae same chemical properties. OR An element has both physical and chemical properties. Physical Properties depends upon the mass numerb so isotopes off an lelement have diffent mass numerb hence they differ in Physical properties, but chemical properties depends upon the number of electrons present in the valence shell of an atom. Number of electrons in isotopes of the element same so they have same chemical properties for all isotopes of the element.

Q6. What is principle of mass spectrometry?
Ans: In this technique, a substance is first vaporized. It is then converted in to gaseous proitive ions with the help of high energy electrons. The gaseous positive ions are sepateated on the basis of their mass to charge  (m/e) ratios. The results are recoreed on the form of peaks. The relative heights of the peaks give the relative abundance of isoptes.

Q7. What is function of electrometer?
Ans: The ions of definite m/e value will move in the form of groups in magnetic analyzer one after the other and fall in the electrometer. The electrometer is also called ion collector. The electrometer develops the electric current. The current strength in each case give the relative abundance of each of the isotopes. The same exe3riment is performed with c-12 isotopes and the current strength is compared. This comparison allow us to measure the exact mass number of the isotope.

Q8. Mention names of techniques which is used for the separations of isotopes.
Ans: The separation of isopopes can be done by different mothods based on their properties. Some important methods are

  1. Gaseous Diffusion
  2. Thermal Diffusion
  3. Ultracentrifuge
  4. Laser Separation
  5. Distillation
  6. Electromagnetic Separation

Q9. What is the justification of two strong peaks in the mass spectra of bromine and one strong peak in mass spectra of iodine?
Ans: Two strong peaks in sase of Bromine shows that is has two isotopes with appromimately equal abundance. i.e. Br-79 and Br-81 is 49.46% while in case of iodine one peak with 100% abundance at 127 indicates that it is moni siptopic mass 127 amu.