FRANK Solutions for Class 9 Chemistry Chapter 7 - Atomic Structure

Chapter 7 - Atomic Structure Exercise 113

Question 1

Compare the characteristics of an electron, proton and neutron.

Solution 1

Question 2

Compare Dalton's atomic theory with Modern Atomic Theory?

Solution 2

Question 3

What is meant by valence shell and valence electron?

Solution 3

The outermost orbit of an element is called valence shell. The electrons present in the outermost orbit (valence shell) of an element are called valence electrons.

Question 4

Why do atoms combine by transferring electrons?

Solution 4

Atoms may have incomplete octet. During the formation of a molecule, an atom of a particular element gains, loses or shares electrons until it acquires a stable configuration of eight electrons in its valence shell.

Question 5

An atom contains 20 protons, 20 electrons and 20 neutrons. Mention the following details of that atom
(a) Atomic number
(b) Mass number
(c) Electronic configuration
(d) Valency

Solution 5

(a) Atomic number = Number of protons = 20    
(b) Mass number = Number of protons +Number of electrons = 20 + 20 = 40
(c) Electronic configuration = 2, 8, 8, 2
(d) Valency = 2

Question 6

(a) What is the valency of each of these five atoms?
(b) Which of these contains the greatest number of neutrons?
(c) Which of these contains the least number of electrons?
(d) Which of these contains equal number of electrons and neutrons?
(e) Which of them is a metal?
(f) Which is the most reactive of the non-metals?
(g) What is common between C and D?
(h) Which of them belongs to a particular family?
(i) If atoms of A combines with atoms of B, what will be the formula of the compound formed?
(j) By what type of valency will B and C combine?

Solution 6

(a) A=1
B=3
C=2
D=1
E=1
(b) E contains the greatest number of neutrons.
(c) A contains the least number of electrons.
(d) B contains equal number of electrons and neutrons.
(e) A is a metal.
(f) Fluorine is the most reactive of the non-metals.
(g) Both are electronegative and non-metals.
(h) D and E belongs to a particular family.
(i) A₃B will be the formula if atoms of A combines with atoms of B.
(j) 'B' will combine in  a trivalent  element while 'C' will combine as a bivalent element.

Question 7

Solution 7

Question 8

Name the constituent particles in the atom that determine the following:
(a) Mass of an atom
(b) Size of an atom

Solution 8

(a) Mass of an atom - Protons and neutrons
(b) Size of an atom - Electrons

Question 9

Name three fundamental particles of an atom.

Solution 9

Three fundamental particles of an atom are-
(a) Proton
(b) Electron
(c) Neutron

Question 10

Define(a) an atom, (b)an element.

Solution 10

(a) An atom - An atom is the smallest particle of an element which may or may not be capable of independent existence.
(b) An element - An element is usually defined as a pure substance that contains only one kind of particles. These particles may be atoms or molecules.

Question 11

What do you mean by the term atomic number and which letter is used to represent it?

Solution 11

Atomic number - The number of protons present in the nucleus of an atom is called the atomic number of the atom.
It is denoted by 'Z'.

Question 12

What are nucleons?

Solution 12

The protons and neutrons are collectively called as nucleons.

Question 13

What are isotopes? Name three isotopes of hydrogen.

Solution 13

Isotopes are atoms of the same element, having the same atomic number, same chemical properties but different mass number, i.e., the atoms differ in the number of neutrons. The three isotopes of hydrogen atoms are-
(i) Protium
(ii) Deuterium
(iii) Tritium

Question 14

Why do isotopes of an element have the same chemical properties?

Solution 14

Electrons take part in a chemical reaction. Therefore, the chemical properties of an element depend upon the electronic configuration. Since, isotopes of an element have the same atomic number and hence same electronic configuration. So, they exhibit the same chemical properties.

Chapter 7 - Atomic Structure Exercise 114

Question 1

What is the octet rule?

Solution 1

"During the formation of the molecule, an atom of a particular element gains, loses electrons or shares electrons until it acquires a stable configuration of eight electrons in its valence shell" i.e. until it acquires octet.

Question 2

What are the maximumnumber of electrons that the K, L and M shells can accommodate?

Solution 2

K can accommodate maximum of 2 electrons.
L can accommodate maximum of 8 electrons.
M can accommodate maximum of 18 electrons.

Question 3

Name the rays which are formed at the negative electrode of the discharge tube experiment?

Solution 3

Cathode rays are formed at the negative electrode of the discharge tube experiment.

Question 4

Calculate the maximum number of electrons which can be accommodated in (i) K, (ii) L (iii) M and (iv) N-shells

Solution 4

(i) In K maximum number of 2 electrons can be accommodated.
(ii) In L maximum number of 8 electrons can be accommodated.
(iii) In M maximum number of 18 electrons can be accommodated.
(iv) In N maximum number of 32 electrons can be accommodated.

Question 5

Solution 5

Question 6

Magnesium (atomic number 12) is a metallic element. Find its valency.

Solution 6

Electronic configuration of magnesium is -2, 8, 2. Since, it has 2 electrons in its valence shell, so its valency is 2.

Question 7

The atomic number and mass number of sodium are 11 and 23 respectively. What information is conveyed by this statement?

Solution 7

Number of electrons in Sodium = 11
Number of protons in sodium = 11
Number of neutrons in sodium = 12
Number of nucleons in sodium = 23

Question 8

What are inert elements? Why do they exist as monoatoms in molecule?

Solution 8

Inert elements are the elements which have completely filled valence shell. Since, they are already stable and do not need more electrons, they do not combine with other atoms. So, they exist as monoatoms in molecule.

Question 9

Name or state the following:
(a) The element which does not contain any neutron in its nucleus.
(b) The shell closest to the nucleus of an atom.
(c) Metal with valency 2.
(d) Two elements having same number of protons and electrons but different number of neutrons.
(e) An element having valency 'zero'.

Solution 9

(a) Hydrogen
(b) K shell.
(c) Magnesium
(d) Isotopes
(e) Helium has zero valency.

Question 10

Solution 10

(a) The number of protons = 9
(b) The number of neutrons = 19 - 9 = 10
(c) The number of electrons = 9

Question 11

Atomic number is unique to an atom, but the mass number is not. Explain this briefly.

Solution 11

Atomic number is the number of protons of an atom which is unique to an atom but mass number is the total of number of protons and number of neutrons which may or may not be same to other atoms since there is probability of combination of number of protons and number of neutrons be same for two atoms.