Chemistry For Class IX (New Book ) - Chapter No. 2- Atomic Structure - Short Questions And Answers

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Chapter No.2- Atomic Structure
Short Questions And Answers
Text Book Exercise

SECTION- B: SHORT QUESTIONS:

1. Draw the structure of isotopes of chlorine to justify the definition of isotopes?
Ans: Isotopes of Chlorine:
There are two isotopes of Chlorine with atomic number 17 and mass number 35 and 37. Chlorine 35 is 75% and chlorine 37 is 25% abundant in nature.

2. An atom has 5 electrons in M shell than:
(a) Find out its atomic number?
(b) Write Electronic configuration of atom?
(c) Name the element of atom?
Ans: Atom has 5 electrons in M shell

(a) Atomic Number:
The atomic number is equal to the total number of proton or electron of an atom, as:,

• Number of maximum electron in K shell = 2
• Number of maximum electron in L shell = 8
• Number of electron in M shell = 5

Total number of electron = 2 + 8 + 5 = 15 is the atomic number of an element.

(b) Electronic configuration of atom:
1s² 2s² 2p⁶ 3s² 3p³

(c) Name the element of atom:
Position in periodic table:

• The outermost shell of element is 3 so it lies in 3^rd Period,
• The Outer most shell has 5 electrons so it lies in Group VA.

So the Name Of an element is Phosphorous (P)

3. Justify that Rutherford atomic model has defects?
Ans: Defects of Rutherford atomic model:

1. Rutherford did not explain the stability of an atom.
2. In Rutherford atomic model the negatively charged electrons revolve around the nucleus in circular path and emits energy continuously. Due to continuous loss of energy ultimately falls into the nucleus.
3. If the revolving electron continuous emits energy, then there would be a continuous spectrum but in contrast to it we get line spectrum from the atoms of elements.

More Short Question Answers

Q.1: Define the following:

• Radioactive elements
• Illumination
• Quantum
• Spectrum

Ans: 1. RADIOACTIVE ELEMENTS:
Radioactive element are unstable isotopes that release subatomic particles or energy as they decay.
For example:
Uranium, Radium and polonium.

2. ILLUMINATION:
Illumination is the action of supplying or brightening with light. It is define as:

"The luminous flux per unit area on an intercepting surface at any given point called illumination."

3. QUANTUM:
A discrete quantity of energy proportion which can exist independently is known as quantum.
In other words,
Electrons are revolving in particular orbits continuously, but they are not emits or absorb energy. When electron jumps from lower energy level (E₁) to higher energy level (E₂), it absorb energy. When electrons jumps from higher energy level (E₂) to lower energy level (E₁), it emits energy. The emission or absorption is discontinuous in the form of energy packet called Quantum or Photon. The energy levels are represented by an integer (n= 1, 2, 3….) known as quantum number, this quantum range starts from nucleus side, where n=1 is lowest energy level.

SPECTRUM:
A Beam of light is allowed to pass through a glass prism, it splits into several colours. This phenomena is called dispersion and band of colours is called spectrum, which is classified according to its wavelength. Such as:

1. Emission Spectra
   (i) Continuous Spectrum
   (ii) Line Spectrum
2. Absorption Spectra

Q.2: Define Modern theories of Atomic Structure?
Ans: Modern Theories of Atomic Structure:

• Max Plank Quantum Theory:
  In the year of 1900 Max Planck proposed quantum nature of radiations and energy in a photon wave E=hν as quantum theory.
• Albert Einstein Theory:
  This quantum theory accepted by Albert Einstein in 1905 and proposed relationship between mass and energy to explain photoelectric effect by wave particle duality as E = mc².
• Neil Bohr Atomic Model:
  In 1913 Neil Bohr continue to use quantization of radiation with angular momentum of electrons. Bohr predict and explain the line spectrum of Hydrogen atom.
• De Broglie Htpothesis:
  In 1923 Lois De Broglie extend the wave particle duality to electron, and propose a hypothesis that all matter has particle as well as wave nature at the submicroscopic level.
• Schrodinger Atomic Model:
  In 1926 Erwin Schrödinger, an Austrian physicist, took the Bohr’s atomic model one step forward. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom.

TEST YOURSELF

a. What is atomic number of an oxygen atom which have 8 electrons and 8 protons?
Ans: Atomic Number Of Oxygen (O):
Data:

• Number of electron = 8
• Number of proton = 8
• Atomic number = Z = ?

Formula:
Atomic Number = Z = Number of proton in nucleus = Total number of electron around nucleus.Ans: Therefore Atomic number of oxygen is 8.

b. Find out mass number of chlorine which have 17 protons and 18 neutrons?
Ans: Solution:
Data:

• Number of proton = Z = 17
• Number of neutron = N =18
• Mass Number = A = ?

Formula:
Mass number = A = Number of protons (Z) + Number of neutrons (N)
A = 17 + 18 = 35

Ans: Therefore, Mass number of chlorine is 35.

c. How many electrons, protons and neutrons are present in Co?
Ans: Solution:
Data:

• Atomic number of Cobalt (Co) = Z = 27
• Mass number of Cobalt (Co) = A = 59
• Number of electron = ?
• Number of proton = ?
• Number of neutron = ?

Formula:
Atomic number= Z = Number of proton in nucleus = Total number of electron around nucleus
Neutron (N) = Mass number (A) - Atomic number (Z)

There fore,

• Number of electron in Cobalt (Co) = Z = 27 Ans.
• Number of proton in Cobalt = =Z = 27 Ans.
• Number of neutron in Cobalt (Co) = N = 59 - 27 = 32 Ans.

d. Do you know any element which have no neutron in its atom?
Ans: Yes, It is an isotope of the element hydrogen called protium, which have no neutron in its atom. Protium which contains a single proton and a single electron, is only stable and the simplest atom.

e. Which particles shows mass of an atom?
Ans: Total number of Proton and Neutron in the nucleus shows mass of an atom.

f. Prove Rutherford atomic model based on classical theory and Bohr atomic model based on quantum theory?
Ans: Rutherford atomic model:
According to the Rutherford atomic model, "The entire mass is concentrated in the nucleus of an atom. The electrons are revolving around the nucleus in circular paths with high speed and emits energy continuously." It based wholly on classical physics. But the Rutherford model itself was superseded in a few years by the Bohr atomic model, due to the fact that continuous loss of energy electron ultimately falls into the nucleus.

Bohr atomic model:
Bohr atomic model predict and explain the line spectrum of Hydrogen atom and based on quantum theory. He explained as, "Electrons are revolving in particular orbits continuously, but they are not emits or absorb energy. When electron jumps from one energy level to another, they emit or absorb energy. The emission or absorption is discontinuous in the form of energy packet called Quantum or Photon."

g. How you can relate living things with chemistry?
Ans: Living Things Relates With Chemistry:
The body of living things based on different elements and compounds which are necessary for life. Such as:

• The water is basic need of human, animals and plants.
• The chemical reactions take place in human, animals and plants.
• Metabolism and synthesis of different substances such as carbohydrates, proteins and fats occurs in the living body are all chemical reactions.
• Living things obtain energy from food by processes like photosynthesis in plants and respiration in all living things.
• Chemistry also tells that how disorder or deficiency of bio-molecules causes diseases.