Chemistry Chapter 2 Short Questions For Class 11 (with Answers)

The most important chemistry chapter 2 short questions for class 11. The 1st-year chapter 2 of chemistry is related to experimental techniques in chemistry. These questions are for the Punjab Textbook Board and can be used within all of Punjab where this syllabus is taught.

Students are advised to prepare these questions in order to perform the best in the board examination.

Chemistry Chapter 2 Short Questions for Class 11

Q.1: State Moseley’s law and also give its mathematical equation.
Ans: Moseley’s law:
“This law states that the frequency of spectral line in x-ray spectrum varies as the square of atomic number of an element emitting it”.
Mathematically;
√v = a (Z – b)
√frequency (v) ∝ Z

What is the importance of Moseley’s law?
Ans: Importance of Moseley’s law:
He concluded that the atomic number “Z” was a fundamental property of an element. It lead to discovery of modern periodic law.
Mosley arranged ‘K’ and ‘Ar’, ‘Ni’ and ‘Co’ in a proper way in Mendeleev’s periodic table.
This law has led to the discovery of many new elements like Tc (43), Pm (61), Rh (45).
The atomic numbers of rare earth metals have been determined by this law.

Q.3: Differentiate between atomic and mass number of an atom?
Ans:

Atomic number	Mass number
“The number of protons present in the nucleus of an atom is called atomic number or proton number.”	“The sum of number of protons and neutrons in the nucleus of an atom is called its nucleon number also called mass number.”
It is denoted by (Z).	It is denoted by (A).
Chemical properties of an element are determined by its atomic number.	Physical properties of an element are determined by its mass number.

Q.4: How can we calculate the number of neutrons in an atom?
Ans: Calculation of number of neutrons:
Number of neutrons in an atom can be calculated as;
N = A – Z
Let us consider ²⁷₁₃Al,
Atomic number / proton number (Z) = 13
Mass number / nucleon number (A) = 27
N = 27 – 13 = 14

Q.5: How can we calculate the number of proton, electron and neutrons in an ion?
Ans: Calculation of number of electrons and protons:
The number of electrons, protons, and neutrons can be justified for an ion as in the following example:
Example:
²⁷₁₃Al atom loses three electrons to form Al³⁺, then;
Atomic number = No. of protons = 13
No. of neutrons = N = A – Z
N = (27 – 13) = 14
No. of protons = No. of electrons = 13
When “Al” atom loses three electrons to form Al³⁺, then
No of electrons = 13 – 3 = 10

Q.6: How fundamental particles of atom are deflected in electric field?
Ans: Deflection of particles:
Neutrons being neutral are not deflected but travel in a straight path perpendicular to the direction of electric field.
Protons being positively charged are deflected towards the negative plate.
Electrons being negatively charged are deflected towards the positive plate, to greater extent since they are 1/1836 times lighter than protons.

Q.7: Write the factors affecting the extent of deflection?
Ans: Extent of deviation:
The amount of deviation from its original direction of movement is measured in two ways.
(i) Angle of deflection ∝ charge / mass
(ii) Radius of deflection ∝ mass / charge
This is possible if we imagine that after deflection, the particle moves in a circular path. Hence, the factors affecting the radius of deflection are reciprocal to that for the angle of deflection.

Q.8: What is atomic emission spectrum?
Ans: Atomic emission spectrum:
When an element in its gaseous state is heated to high temperatures or subjected to electrical discharge, radiation of certain wavelengths is emitted. The spectrum of this radiation contains coloured lines and is called atomic emission spectrum.

Q.9: What is atomic absorption spectrum?
Ans: Atomic absorption spectrum:
When a beam of white light is passed through a gaseous sample of an element in cold state, certain wavelengths are absorbed. The wavelengths of the white light that has been absorbed by the atoms show up as dark lines on the spectrum. The spectrum of this radiation is called an atomic absorption spectrum.

Q.10: Atomic spectra are the finger prints of elements. justify?
Ans: Atomic spectra are the finger prints of the elements:
Each element has a unique arrangement of electrons and thus a unique range of fixed energy levels. It follows that the wavelengths and frequencies of the radiation absorbed or emitted when electrons jump from one energy level to another must also be unique. This uniqueness convinces us to conclude that every element has its own characteristic spectrum. Therefore, every element is identified by its characteristic spectrum. Hence, we can say that atomic spectra are the finger prints of the elements.

Q.37: Differentiate between atomic emission and atomic absorption spectrum?
Ans:

Atomic Emission Spectrum	Atomic Absorption Spectrum
When an element in its gaseous state is heated to high temperatures or subjected to electrical discharge, radiation of certain wavelengths is emitted. The spectrum of this radiation contains coloured lines and is called atomic emission spectrum.	When a beam of white light is passed through a gaseous sample of an element in cold state, certain wavelengths are absorbed. The wavelengths of the white light that has been absorbed by the atoms show up as dark lines on the spectrum. The spectrum of this radiation is called an atomic absorption spectrum.
The atomic emission spectrum contains bright lines against a dark background.	The atomic absorption spectrum contains dark lines and the background is bright.

Q.12: What is principal quantum number?
Ans: Principal quantum number:
The quantum number which represent the main energy level or main shell in which an electron revolves around the nucleus is called principal quantum number.

It is denoted by ‘n’.
Its values are non zero positive integers upto infinity.
e.g., n = {1, 2, 3, 4, ……… ∞}

Q.13: What is the significance of principal quantum number?
Ans: Principal quantum number:
The quantum number which represent the main energy level or main shell
Significance:

It determines the average distance of electron is an atom from the nucleus.
It gives a quantitative measure of the size an electronic shell.
It also provides us the energy of electron in a shell.
The value of “n” also gives the maximum number of electrons, which can be accommodated in a shell by the formula “2n²”

Q.14: What is azimuthal quantum number?
Ans: Azimuthal quantum number:
The quantum number which tells us about the number of sub-shells present in a main shell of an atom, in which electrons can revolve around the nucleus, is called azimuthal quantum number.

It is denoted by “ℓ”.
ℓ = {0, 1, 2, 3}
The value of “ℓ” depends upon “n” and it always start from zero.
The values of “ℓ” for a given shell = {0…….. (n – 1)}
These values represent different sub shells, which are denoted by small letters, s, p, d and f. They stand for sharp, principal, diffused and fundamental respectively.

Q.15: Why ‘f’ subshell can accommodate fourteen electrons? Explain.
Ans: ‘f’ subshell can accommodate fourteen electrons:
According to Azimuthal quantum number, the total number of electrons in a given sub-shell can be calculated by the formula 2(2ℓ + 1).
The value of Azimuthal quantum number “ℓ” for ‘f’ subshell is 3.
Putting the value in the above formula,
Number of electrons = 2 (2ℓ + 1)
Number of electrons = 2 (2 x 3 + 1)
= 2 x (7) = 14
Thus ‘f’ subshell can accommodate only fourteen electrons.

Q.16: What is magnetic quantum number?
Ans: Magnetic quantum number:
The quantum number, which describes the number of orientations of orbitals in space within a sub-shell of main shell is called as magnetic quantum number and it is denoted by ‘m’.

It is also called as orbital orientation quantum number.
The value of ‘m’ range from m = {-ℓ,…0,…+ ℓ}
Magnetic quantum number ‘m’ represents the total no. of different space orientations for a sub-shell.
It can also be calculated by the formula (2ℓ + 1).

Q.17: What are degenerate orbitals?
Ans: Degenerate Orbitals:
Orbitals of a sub-shell, which have same energy but different orientation in space, are called as degenerate orbitals.

This phenomenon is called as degeneracy.
Example:
2px, 2py, 2pz are said to be degenerate orbitals of 2p sub-shell.

Q.18: What is spin quantum number?
Ans: Spin quantum number:
“The quantum number which tells us about the rotation of electrons around its own axis is called as spin quantum”

It is denoted by (s).
The value of ‘s’ range from {-1/2 to +1/2 }
The value of spin quantum number is -1/2 for clockwise direction and +1/2 for anti-clock rotation.

Q.19: Differentiate between orbit and orbital?
Ans:

ORBIT	ORBITAL
It is a definite circular path at a fixed distance from the nucleus on which the electron is revolving around the nucleus.	It is a three dimensional region or space around the nucleus in which the probability of finding an electron is maximum (95%)
Orbits are supposed to have a circular shape.	Orbitals have different shapes e.g., s-orbital is spherically symmetrical while p-orbitals are dumb-bell shaped.
Orbits represent the planar motion of the electron.	Orbitals represent three dimensional motion of the electron.
The maximum number of electrons in an orbit is equal to 2n², where n is equal to the number of the orbit.	The maximum number of electrons in an orbital is equal to 2.

Q.20: Draw the shapes of p-orbitals.
Ans: Shapes of p-orbitals:
For p-subshell, ℓ = 1, so there are three values of m = {-1, 0, +1}.
It means p-subshells have three orientations or orbitals i.e., {2px, 2py, 2pz}
All the p-orbitals of all the energy levels have similar shapes but with the increase of principal quantum number of the shell, their sizes are increased.

Q.21: Draw the shapes of d-orbitals.
Ans: Shapes of d-orbitals:
For d sub shell, If ℓ = 2, there are five values of m = {-2, -1, 0, +1, +2}.
It means d-subshells have 5 orbitals. {dxy, dyz, dxz, dx²-y², dz²}

Q.22: What do you mean by electronic configuration of elements.
Ans: Electronic configuration:
“Electronic configuration is the distribution of electrons among available shells, subshells, or orbitals of an atom or ion.”
Note:

Each group of orbitals in a subshell is labeled by its subshell notation.
An electron in an orbital is shown by an arrow.
The arrow points upward, when s = +½ and downward when s = -½.
Example:
₁₁B = 1s 2s 2px 2py 2pz (with arrows showing spin)

Q.23: State Aufbau principle?
Ans: Aufbau principle:
Aufbau principle is also known as the building up principle.
This principle says that the subshells in an atom are filled with electrons in an increasing order of their energy values. Now, question arises that how to arrange the subshells energy wise.

Q.24: State (n + ℓ) rule.
Ans: (n + ℓ) Rule:
This rule states that;
“Sub-shells are arranged in increasing order of their (n+ℓ) values, and if any two sub-shells have same (n + ℓ) value, them that sub-shell is placed first whose n value is smaller”.
The (n + ℓ) value of different sub-shells can be calculated from principal and azimuthal quantum number.

Q.25: Give the rules for applying (n + ℓ) rule.
Ans: Rules for applying (n+ℓ) rule:
Following rules must be considered while applying (n + ℓ) rule.
Rule # 1:
The subshell having lower (n + ℓ) value has lower energy and is filled first.
Rule # 2:
In case there are two subshells are having equal (n + ℓ) values, then the subshell with lower ‘n’ value will be filled first.
For example,
Both 4p and 3d subshells have (n + ℓ) value equal to 5 (4p = 4 + 1 = 5) and (3d = 3 + 2 = 5); 3d subshell will be preferred to be filled because of its low “n” value.

Q.26: State Pauli’s exclusion principle?
Ans: Pauli’s exclusion principle:
Pauli’s exclusion principle can be stated as follows.
“It is impossible for two electrons residing in the same orbital of a poly-electron atom to have the same values of four quantum numbers”.
OR
Two electrons revolving in the same orbital must have opposite spins↕.
Example:
₂He = 1s ↕

Q.27: How distribution of electrons in orbitals are represented by box diagrams.
Ans: Distribution of electrons in orbitals:
The filling of electrons in orbitals is represented by box diagrams, where each box represents an orbital.

Each box represents an atomic orbital.
Each orbital can occupy maximum of two electrons.
An electron is represented by an arrow.
The boxes (orbitals) can be arranged in order of increasing energy from bottom to top.
(Diagram showing 1s, 2s, 2p configuration for Boron)

Q.28: State Hund’s rule with one example?
Ans: Hund’s rule:
Hund’s rule states that,
“When degenerate orbitals are available and more than two electrons are to be placed in them, they should be placed in separate orbitals with the same spin rather than in the same orbital with opposite spins.”
This rule gives an idea for filling electrons into the orbitals having equal energies.
For example,
N = 1s², 2s², 2px¹, 2py¹, 2pz¹

Q.29: What are free radicals?
Ans: Free radicals:
“A free radical is a species (an atom or group of atoms) that has one or more unpaired electrons”.
Examples:
An example of a simple free radical is free chlorine atom :Ċl:. The electron configuration of this radical is 1s² 2s² 2p⁶ 3s² 3p⁵. In the 2p subshell, two orbitals have paired electrons whereas, the third one contains a single unpaired electron. The unpaired electron is shown by a single dot as in Cl•.
Apart from single atoms, groups of atoms can also be free radicals.
For example:
OH•, CH₃•, etc.

Q.30: What are semiconductors? Give its use.
Ans: Semiconductors:
“Semiconductors are materials that can conduct electricity under some conditions.”
Example:
Examples of the elements that can act as semiconductors are silicon, germanium and arsenic etc.
Uses:
They are used in many electronic devices, including smartphones, laptops, and cars.

Q.31: How doping of silicon is done for the preparation of semiconductors?
Ans: Types of semi-conductors:
P-type and N-type semiconductors are formed by “doping” a pure semiconductor material with impurity atoms, where adding trivalent impurities (like boron or aluminum) creates a P-type semiconductor, while adding pentavalent impurities (like phosphorus or arsenic) creates an N-type semiconductor. The difference lies in whether the added impurity creates “holes” (positive charge carriers) in the lattice, leading to P-type, or extra electrons (negative charge carriers) leading to N-type.

Q.32: What are P-type semiconductors and how they are formed?
Ans: Formation of P-type semiconductor:
Impurity atoms with three valence electrons (like Al) are added to the pure semiconductor. Some of the trivalent atoms take place of the Si atoms in the crystals. The silicon atoms cannot make four bonds due to the lack of electrons. For this reason, there are created holes in the crystal lattice, which act as positive charge carriers. This process creates a positive-type semiconductor or P-type semiconductor. Electrons from an external current source can move through the semiconductor and it can act as a conductor.

Q.33: What are N-type semiconductors and how they are formed?
Ans: Formation N-type semiconductor:
When impurity atoms with five valence electrons (like phosphorus) are added to the pure semiconductor, some of Si atoms are replaced with the pentavalent phosphorus atoms. The Si atoms in the vicinity of these atoms can make four bonds and the fifth electron is an extra electron. These impurity atoms contribute extra electrons to the crystal lattice, which become free to move and act as negative charge carriers as in Figure. The result is an N-type semiconductor that can conduct electricity when connected to an external source.