Structure of Atom

Electronic Configurations

Atomic Models

Quantum Mechanical Model

Electromagnetic Radiation and Quantum Theory

Atomic Spectra

Electron Configuration Principles

Photoelectric Effect

De Broglie Wavelength and Matter Waves

Heisenberg Uncertainty Principle

Atomic and Ionic Symbols

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CBSE Learning Objectives – Key Concepts & Skills You Must Know

Learning Objectives

Understand the electronic configurations of elements, including exceptional configurations, and their implications on chemical properties.
Describe the historical atomic models including Thomson, Rutherford, and Bohr models, and their contributions to modern atomic theory.
Explore the quantum mechanical model of the atom, including quantum numbers and their significance in defining atomic orbitals.
Understand the nature of electromagnetic radiation and Planck's quantum theory, and their applications in explaining phenomena like the photoelectric effect.
Study atomic spectra, including the Balmer series and transitions in hydrogen and helium ions, and their significance in atomic structure.
Apply the aufbau principle, Pauli exclusion principle, and Hund's rule in determining the electronic configurations of atoms.
Explain the photoelectric effect, including calculations of work function, threshold frequency, and kinetic energy of ejected electrons.
Understand the concept of matter waves and de Broglie wavelength, and their implications in technologies like electron microscopes.
Explore the Heisenberg uncertainty principle and its implications on the precision of measurements in quantum mechanics.
Determine atomic and ionic symbols based on mass number, atomic number, and charge, including isotopic and isoelectronic species.

CBSE Revision Notes & Quick Summary for Last-Minute Study

Chapter Notes

Electronic Configurations

Electronic Configurations: The arrangement of electrons in an atom's orbitals.
Exceptional Configurations: Some elements like Chromium (Cr) and Copper (Cu) have unique configurations due to electron stability preferences.
Table of Configurations: Provides configurations for elements like H, He, Li, etc., showing the filling order of orbitals.

Atomic Models

Thomson Model: Proposed the 'plum pudding' model where electrons are embedded in a positive sphere.
Rutherford Model: Introduced the nuclear model with a dense positive nucleus.
Bohr Model: Introduced quantized orbits for electrons, explaining atomic spectra.

Quantum Mechanical Model

Quantum Numbers: Define the properties of atomic orbitals and electrons:
- Principal Quantum Number (n): Indicates the size and energy level of the orbital.
- Azimuthal Quantum Number (l): Defines the shape of the orbital.
- Magnetic Quantum Number (mₗ): Orientation of the orbital in space.
- Spin Quantum Number (mₛ): Indicates the spin direction of the electron.

Electromagnetic Radiation and Quantum Theory

Electromagnetic Radiation: Waves of electric and magnetic fields; includes visible light.
Planck's Quantum Theory: Energy is quantized and emitted in discrete units called quanta.

Atomic Spectra

Balmer Series: Visible spectrum of hydrogen; transitions to n=2.
Significance: Provides evidence for quantized energy levels in atoms.

Electron Configuration Principles

Aufbau Principle: Electrons fill orbitals starting from the lowest energy level.
Pauli Exclusion Principle: No two electrons can have the same set of four quantum numbers.
Hund's Rule: Electrons fill degenerate orbitals singly before pairing.

Photoelectric Effect

Explanation: Ejection of electrons from a metal when light shines on it.
Key Calculations: Work function, threshold frequency, and kinetic energy of ejected electrons.

De Broglie Wavelength and Matter Waves

Matter Waves: Particles like electrons exhibit wave-like properties.
De Broglie Wavelength: λ = h/p, where h is Planck's constant and p is momentum.

Heisenberg Uncertainty Principle

Principle: It is impossible to simultaneously know the exact position and momentum of a particle.

Atomic and Ionic Symbols

Determination: Based on mass number, atomic number, and charge.
Isoelectronic Species: Species with the same number of electrons, e.g., Na⁺, Mg²⁺.

CBSE Exam Tips, Important Questions & Common Mistakes to Avoid

Common Mistakes & Exam Tips

Electronic Configurations

Mistake: Students often forget about exceptional electronic configurations, such as those for chromium (Cr) and copper (Cu), which do not follow the expected order.
- Tip: Memorize the common exceptions and understand the reasons behind them, such as increased stability due to half-filled and fully filled subshells.

Atomic Models

Mistake: Confusion between the contributions of different atomic models (Thomson, Rutherford, Bohr).
- Tip: Create a timeline of atomic model developments and summarize each model's key contributions and limitations.

Quantum Mechanical Model

Mistake: Misunderstanding the significance of quantum numbers and their role in defining atomic orbitals.
- Tip: Practice writing out the quantum numbers for various electrons and use diagrams to visualize orbitals.

Electromagnetic Radiation and Quantum Theory

Mistake: Difficulty in applying Planck's quantum theory to phenomena like the photoelectric effect.
- Tip: Work through numerical problems involving energy, frequency, and wavelength to solidify understanding.

Atomic Spectra

Mistake: Forgetting the significance of series like the Balmer series in hydrogen.
- Tip: Use mnemonic devices to remember the order of spectral series and their corresponding transitions.

Electron Configuration Principles

Mistake: Incorrect application of the aufbau principle, Pauli exclusion principle, and Hund's rule.
- Tip: Practice filling electron configurations for elements across the periodic table, paying special attention to the order of orbital filling.

Photoelectric Effect

Mistake: Errors in calculations involving work function, threshold frequency, and kinetic energy.
- Tip: Ensure a strong grasp of the equations involved and practice with a variety of numerical problems.

De Broglie Wavelength and Matter Waves

Mistake: Overlooking the implications of matter waves in practical applications like electron microscopes.
- Tip: Relate the concept of de Broglie wavelength to real-world technologies to better understand its significance.

Heisenberg Uncertainty Principle

Mistake: Misinterpreting the principle's implications on measurement precision.
- Tip: Use thought experiments to explore the principle's meaning and limitations.

Atomic and Ionic Symbols

Mistake: Confusion in determining atomic and ionic symbols, especially for isotopic and isoelectronic species.
- Tip: Practice writing symbols and configurations for a variety of ions and isotopes to gain confidence.

CBSE Quiz & Practice Test – MCQs, True/False Questions with Solutions

Multiple Choice Questions

It explains the behavior of light as only waves.

It describes light as having both wave-like and particle-like properties.

It suggests that light behaves only as particles.

It implies that light cannot be quantified.

Correct Answer: B

Solution:

Wave-particle duality is a fundamental concept in quantum mechanics that describes light as having both wave-like and particle-like properties, which is crucial in explaining phenomena like the photoelectric effect.

Chapter Concept:

Electromagnetic Radiation and Quantum Theory

1.21 \times 10^{-10} \text{ m}

4.84 \times 10^{-10} \text{ m}

2.42 \times 10^{-10} \text{ m}

1.21 \times 10^{-9} \text{ m}

Correct Answer: A

Solution:

For a particle with mass

2m

, the de Broglie wavelength

\lambda = \frac{h}{2mv}

. Using the previous values:

\lambda = \frac{6.626 \times 10^{-34}}{2 \times 9.109 \times 10^{-31} \times 1 \times 10^6} = 1.21 \times 10^{-10} \text{ m}

Chapter Concept:

De Broglie Wavelength and Matter Waves

The uncertainty in momentum increases.

The uncertainty in momentum decreases.

The uncertainty in momentum remains the same.

The uncertainty in momentum becomes zero.

Correct Answer: A

Solution:

According to the Heisenberg uncertainty principle,

\Delta x \Delta p \geq \frac{h}{4\pi}

, where

\Delta x

is the uncertainty in position and

\Delta p

is the uncertainty in momentum. If

\Delta x

is reduced,

\Delta p

must increase to satisfy the inequality.

Chapter Concept:

Heisenberg Uncertainty Principle

It determines the energy level of an electron.

It specifies the shape of the electron's orbital.

It indicates the orientation of the orbital in space.

It defines the spin of the electron.

Correct Answer: B

Solution:

The quantum number

l

, known as the azimuthal quantum number, specifies the shape of the electron's orbital.

Chapter Concept:

Electronic Configurations

Correct Answer: C

Solution:

Oxygen has the electronic configuration

1s^2 2s^2 2p^4

, with two unpaired electrons in the 2p subshell.

Chapter Concept:

Electronic Configurations

In elliptical orbits

In circular orbits

In random paths

In stationary positions

Correct Answer: B

Solution:

Bohr's model postulated that electrons move around the nucleus in circular orbits, each corresponding to a specific energy level.

Chapter Concept:

Atomic Models

It could not explain the stability of the atom.

It did not account for the existence of protons.

It ignored the wave nature of electrons.

It proposed that electrons are stationary.

Correct Answer: A

Solution:

Rutherford's model could not explain why the electron does not fall into the nucleus, thus failing to account for the stability of the atom.

Chapter Concept:

Atomic Models

Principal quantum number (

n

)

Azimuthal quantum number (

l

)

Magnetic quantum number (

m_l

)

Spin quantum number (

s

)

Correct Answer: D

Solution:

The quantum mechanical model of the atom includes the principal quantum number (

n

), azimuthal quantum number (

l

), and magnetic quantum number (

m_l

). The spin quantum number (

s

) is not part of the Schrödinger equation solution for hydrogen.

Chapter Concept:

Quantum Mechanical Model

Electrons are emitted with kinetic energy.

Electrons are emitted without kinetic energy.

No electrons are emitted.

The metal heats up but no electrons are emitted.

Correct Answer: C

Solution:

No electrons are emitted because the frequency of the light is below the threshold frequency required to eject electrons.

Chapter Concept:

Photoelectric Effect

0.5 V

1.0 V

1.5 V

2.0 V

Correct Answer: C

Solution:

The energy of the incident photon is given by

E = h \nu

. Substituting the given values,

E = 6.626 \times 10^{-34} \times 8 \times 10^{14} = 5.301 \times 10^{-19} \text{ J}

. Converting this to eV,

E = \frac{5.301 \times 10^{-19}}{1.602 \times 10^{-19}} = 3.31 \text{ eV}

. The kinetic energy of the ejected electrons is

K.E. = E - \phi = 3.31 \text{ eV} - 3 \text{ eV} = 0.31 \text{ eV}

. The stopping potential

V_0

is given by

K.E. = eV_0

, thus

V_0 = 0.31 \text{ V}

Chapter Concept:

Photoelectric Effect

Aufbau principle

Pauli exclusion principle

Hund's rule

Heisenberg uncertainty principle

Correct Answer: A

Solution:

The Aufbau principle states that electrons fill orbitals starting from the lowest energy level. Adding an electron to the

4s

orbital before filling the

4p

orbital violates this principle.

Chapter Concept:

Electron Configuration Principles

Energy is emitted or absorbed in discrete units called quanta.

Energy is continuous and can be emitted or absorbed in any amount.

Electrons orbit the nucleus in fixed paths.

Atoms are indivisible particles.

Correct Answer: A

Solution:

Planck's quantum theory states that energy is emitted or absorbed in discrete units called quanta.

Chapter Concept:

Electromagnetic Radiation and Quantum Theory

6.626 \times 10^{-31} \text{ kg}

3.313 \times 10^{-31} \text{ kg}

1.325 \times 10^{-30} \text{ kg}

9.109 \times 10^{-31} \text{ kg}

Correct Answer: B

Solution:

Using the de Broglie wavelength formula

\lambda = \frac{h}{mv}

, rearrange to find mass

m = \frac{h}{\lambda v}

. Substituting the given values:

m = \frac{6.626 \times 10^{-34}}{5 \times 10^{-10} \times 2 \times 10^6} = 3.313 \times 10^{-31} \text{ kg}

Chapter Concept:

De Broglie Wavelength and Matter Waves

The electron's distance from the nucleus

The electron's speed

The electron's mass

The electron's charge

Correct Answer: A

Solution:

In Bohr's model, the energy of an electron is determined by its orbit, which is defined by its distance from the nucleus. Each orbit corresponds to a specific energy level.

Chapter Concept:

Atomic Models

1s^2 2s^2 2p^4

1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 6s^2 4f^{14} 5d^{10} 6p^6 7s^2

1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 6s^2 4f^{14} 5d^{10} 6p^6 7s^2 5f^{14} 6d^{10} 7p^6

1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2 4d^{10} 5p^6 6s^2 4f^{14} 5d^{10} 6p^6 7s^2 5f^{15}

Correct Answer: D

Solution:

The Pauli exclusion principle states that no two electrons in an atom can have the same set of four quantum numbers. The configuration in option D has

5f^{15}

, which violates this principle as the

f

subshell can hold a maximum of 14 electrons.

Chapter Concept:

Electron Configuration Principles

Thomson's plum pudding model

Rutherford's nuclear model

Bohr's planetary model

Schrödinger's quantum mechanical model

Correct Answer: B

Solution:

Rutherford's nuclear model introduced the concept of a tiny positively charged nucleus at the center of the atom, with electrons revolving around it.

Chapter Concept:

Atomic Models

Emission of electrons when light strikes a material.

Scattering of alpha particles by a thin foil.

Absorption of light by electrons in an atom.

Reflection of light from a surface.

Correct Answer: A

Solution:

The photoelectric effect explains the emission of electrons when light strikes a material.

Chapter Concept:

Electromagnetic Radiation and Quantum Theory

Diamagnetic, as all electrons are paired.

Paramagnetic, due to one unpaired electron.

Ferromagnetic, due to multiple unpaired electrons.

Antiferromagnetic, due to alternating spins.

Correct Answer: B

Solution:

The electronic configuration

1s^2 2s^2 2p^6 3s^2 3p^5

indicates one unpaired electron in the

3p

subshell, making the atom paramagnetic according to Hund's rule.

Chapter Concept:

Electron Configuration Principles

Aufbau Principle

Pauli Exclusion Principle

Hund's Rule

Heisenberg Uncertainty Principle

Correct Answer: B

Solution:

The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of four quantum numbers.

Chapter Concept:

Electronic Configurations

Mass

Velocity

Wavelength

Charge

Correct Answer: C

Solution:

De Broglie's hypothesis states that particles of matter have an associated wavelength, known as the de Broglie wavelength, which is a manifestation of wave-particle duality.

Chapter Concept:

De Broglie Wavelength and Matter Waves

[Ar] 3d^{10} 4s^2 4p^1

[Ar] 3d^{5} 4s^1

[Kr] 4d^{10} 5s^2 5p^3

[Xe] 4f^{14} 5d^{10} 6s^2

Correct Answer: B

Solution:

The electronic configuration

[Ar] 3d^{5} 4s^1

is an exception to the Aufbau principle due to the half-filled stability of the

3d

subshell in chromium.

Chapter Concept:

Electronic Configurations

Energy is emitted or absorbed in continuous waves.

Energy is emitted or absorbed in discrete packets called quanta.

Energy levels are continuous and can have any value.

Energy is only emitted in the form of visible light.

Correct Answer: B

Solution:

Planck's quantum theory states that energy is quantized and is emitted or absorbed in discrete packets called quanta, not in a continuous manner.

Chapter Concept:

Electromagnetic Radiation and Quantum Theory

7.28 \times 10^{-10} \text{ m}

1.21 \times 10^{-9} \text{ m}

2.42 \times 10^{-10} \text{ m}

3.63 \times 10^{-10} \text{ m}

Correct Answer: A

Solution:

Chapter Concept:

De Broglie Wavelength and Matter Waves

Both properties can be measured with absolute certainty simultaneously.

The more precisely one property is measured, the less precisely the other can be known.

Both properties cannot be measured at all.

The principle applies only to macroscopic objects.

Correct Answer: B

Solution:

The Heisenberg uncertainty principle states that the more precisely the position of a particle is determined, the less precisely its momentum can be known, and vice versa.

Chapter Concept:

Heisenberg Uncertainty Principle

[Ar] 3d^{10} 4s^1

; it is a transition metal with high electrical conductivity.

[Ar] 3d^9 4s^2

; it is a poor conductor of electricity.

[Ar] 3d^{10} 4s^2

; it is a noble gas.

[Ar] 3d^8 4s^2

; it is a metalloid.

Correct Answer: A

Solution:

The electronic configuration

[Ar] 3d^{10} 4s^1

corresponds to copper (atomic number 29), which is a transition metal known for its excellent electrical conductivity.

Chapter Concept:

Electronic Configurations

Only the principal quantum number (

n

)

Only the azimuthal quantum number (

l

)

The sum of the principal and azimuthal quantum numbers (

n + l

)

The magnetic quantum number (

m_l

) and spin quantum number (

m_s

)

Correct Answer: C

Solution:

In a multi-electron atom, the energy of an electron is determined by the sum of the principal quantum number (

n

) and the azimuthal quantum number (

l

). The lower the value of (

n + l

), the lower the energy of the orbital.

Chapter Concept:

Quantum Mechanical Model

It cannot explain the stability of the atom.

It ignores the wave nature of electrons.

It does not account for the existence of protons.

It fails to describe the photoelectric effect.

Correct Answer: B

Solution:

The Bohr model treats electrons as particles in fixed orbits and does not consider their wave-like properties, which is a significant limitation.

Chapter Concept:

Atomic Spectra

n=3

n=2

n=4

n=3

n=5

n=4

n=6

n=1

Correct Answer: D

Solution:

The transition from

n=6

n=1

involves the largest energy difference, resulting in the emission of a photon with the shortest wavelength, according to the formula

E = \frac{hc}{\lambda}

Chapter Concept:

Atomic Spectra

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: B

Solution:

The Balmer series corresponds to the transitions of electrons in a hydrogen atom that result in the emission of visible light.

Chapter Concept:

Atomic Spectra

\lambda = \frac{h}{mv}

\lambda = \frac{mv}{h}

\lambda = \frac{h}{v}

\lambda = \frac{h}{m}

Correct Answer: A

Solution:

The de Broglie wavelength

\lambda

is given by the formula

\lambda = \frac{h}{mv}

, where

h

is Planck's constant.

Chapter Concept:

De Broglie Wavelength and Matter Waves

The stability of the atom

The wave-particle duality of electrons

The existence of subatomic particles

The electromagnetic spectrum

Correct Answer: B

Solution:

The Bohr model did not account for the wave-particle duality of electrons, which was later addressed by quantum mechanics through the Schrödinger equation.

Chapter Concept:

Atomic Models

All orbitals within a given shell have the same energy in multi-electron atoms.

The energy of orbitals in multi-electron atoms depends on the values of

n

and

l

Orbitals are clearly defined paths around the nucleus.

Orbitals are the same as orbits in the Bohr model.

Correct Answer: B

Solution:

In multi-electron atoms, the energy of orbitals depends on the values of

n

and

l

. The lower the value of

(n + l)

, the lower the energy. If two orbitals have the same

(n + l)

value, the orbital with the lower

n

has lower energy.

Chapter Concept:

Quantum Mechanical Model

^{12}_6C

^{12}_6N

^{6}_6C

^{6}_6N

Correct Answer: A

Solution:

The atomic symbol

^{12}_6C

represents a carbon atom with 6 protons and 6 neutrons, giving it a mass number of 12.

Chapter Concept:

Atomic and Ionic Symbols

The energy required to remove an electron from the surface of a metal.

The frequency of light needed to emit electrons from a metal surface.

The kinetic energy of ejected electrons.

The wavelength of light used in the photoelectric effect.

Correct Answer: A

Solution:

The work function is the minimum energy required to remove an electron from the surface of a metal in the photoelectric effect.

Chapter Concept:

Photoelectric Effect

Nitrogen (

1s^2 2s^2 2p^3

)

Oxygen (

1s^2 2s^2 2p^4

)

Carbon (

1s^2 2s^2 2p^2

)

Fluorine (

1s^2 2s^2 2p^5

)

Correct Answer: B

Solution:

Oxygen's electronic configuration

1s^2 2s^2 2p^4

can be written as

1s^2 2s^2 2p_x^2 2p_y^1 2p_z^1

, which follows Hund's rule. However, if the electrons were paired in the same orbital, it would violate Hund's rule.

Chapter Concept:

Electronic Configurations

Copper (

Cu

)

Neon (

Ne

)

Helium (

He

)

Argon (

Ar

)

Correct Answer: A

Solution:

Copper has an exceptional electronic configuration of

[Ar] 3d^{10} 4s^1

due to the stability of a filled d subshell.

Chapter Concept:

Electronic Configurations

Dalton's Model

Thomson's Model

Rutherford's Model

Bohr's Model

Correct Answer: B

Solution:

Thomson's model, also known as the 'plum pudding model', proposed that an atom consists of a uniform sphere of positive charge with electrons embedded into it.

Chapter Concept:

Atomic Models

1.72 eV

2.48 eV

3.10 eV

4.02 eV

Correct Answer: A

Solution:

The energy of the incident photon is given by

E = \frac{hc}{\lambda}

. Substituting the given values,

E = \frac{6.626 \times 10^{-34} \times 3 \times 10^{8}}{200 \times 10^{-9}} = 9.939 \times 10^{-19} \text{ J}

. Converting this to eV,

E = \frac{9.939 \times 10^{-19}}{1.602 \times 10^{-19}} = 6.20 \text{ eV}

. The maximum kinetic energy of the ejected electrons is

K.E. = E - \phi = 6.20 \text{ eV} - 4.5 \text{ eV} = 1.70 \text{ eV}

Chapter Concept:

Photoelectric Effect

Principal quantum number (

n

)

Azimuthal quantum number (

l

)

Magnetic quantum number (

m_l

)

Spin quantum number (

m_s

)

Correct Answer: B

Solution:

The azimuthal quantum number (

l

) defines the shape of the atomic orbital. It determines the subshell in which the electron resides, and each value of

l

corresponds to a different orbital shape (s, p, d, f).

Chapter Concept:

Quantum Mechanical Model

124 nm

1240 nm

12400 nm

124000 nm

Correct Answer: A

Solution:

The energy of the photon is 10 eV. Using the formula

E = \frac{hc}{\lambda}

, we can solve for

\lambda

\lambda = \frac{hc}{E} = \frac{4.135667696 \times 10^{-15} \times 3 \times 10^8}{10} = 124 \ nm

Chapter Concept:

Atomic Spectra

The uncertainty in position decreases.

The uncertainty in position increases.

The uncertainty in position remains the same.

The uncertainty in position becomes zero.

Correct Answer: A

Solution:

According to the Heisenberg uncertainty principle,

\Delta k \Delta x \geq \frac{1}{2}

, where

\Delta k

is the uncertainty in wave number and

\Delta x

is the uncertainty in position. Increasing

\Delta k

results in a decrease in

\Delta x

to satisfy the inequality.

Chapter Concept:

Heisenberg Uncertainty Principle

Discovery of the neutron

Quantized energy levels

Existence of protons

Formation of chemical bonds

Correct Answer: B

Solution:

Solving the Schrödinger equation for the hydrogen atom results in quantized energy levels. These energy levels are characterized by quantum numbers and describe the allowed states for the electron.

Chapter Concept:

Quantum Mechanical Model

Na^+

F^-

O^{2-}

All of the above

Correct Answer: D

Solution:

All the ions

Na^+

F^-

, and

O^{2-}

have 10 electrons, making them isoelectronic with the noble gas neon (

Ne

), which also has 10 electrons.

Chapter Concept:

Atomic and Ionic Symbols

Heisenberg uncertainty principle

Pauli exclusion principle

Hund's rule

Aufbau principle

Correct Answer: B

Solution:

The Pauli exclusion principle states that no two electrons in the same atom can have identical sets of four quantum numbers. This principle is crucial for defining the electronic structure of atoms.

Chapter Concept:

Quantum Mechanical Model

Electron microscope

Optical telescope

Radio telescope

Thermal camera

Correct Answer: A

Solution:

The electron microscope uses the concept of matter waves, specifically the wave nature of electrons, to achieve high resolution.

Chapter Concept:

De Broglie Wavelength and Matter Waves

The principal quantum number

n

only.

The azimuthal quantum number

l

only.

The sum of

n

and

l

values.

The magnetic quantum number

m_l

only.

Correct Answer: C

Solution:

In a multi-electron atom, the energy of an electron is determined by the sum of the principal quantum number

n

and the azimuthal quantum number

l

Chapter Concept:

Electromagnetic Radiation and Quantum Theory

1s^2 2s^2 2p^2

1s^2 2s^2 2p^4

1s^2 2s^2 2p^6

1s^2 2s^2 3s^2

Correct Answer: A

Solution:

The correct electron configuration for a carbon atom is

1s^2 2s^2 2p^2

Chapter Concept:

Electron Configuration Principles

Electrons should pair up in each orbital before moving to the next.

Electrons should fill the lowest energy orbitals first.

Electrons should occupy empty orbitals singly before pairing up.

Electrons should be distributed randomly.

Correct Answer: C

Solution:

Hund's rule states that electrons should occupy empty orbitals singly before pairing up in orbitals of the same energy.

Chapter Concept:

Electron Configuration Principles

1s^2 2s^2 2p^6 3s^1

1s^2 2s^2 2p^6 3p^1

1s^2 2s^2 2p^5 3s^2

1s^2 2s^2 2p^6 3s^2

Correct Answer: A

Solution:

The element with atomic number 11 is sodium, and its electronic configuration is

1s^2 2s^2 2p^6 3s^1

Chapter Concept:

Electronic Configurations

Aufbau principle

Pauli exclusion principle

Hund's rule

Heisenberg uncertainty principle

Correct Answer: B

Solution:

The Pauli exclusion principle states that no two electrons in the same atom can have the same set of quantum numbers.

Chapter Concept:

Quantum Mechanical Model

Emission of electrons from a metal surface when exposed to light of sufficient frequency.

Absorption of photons by electrons in an atom, causing them to jump to higher energy levels.

Scattering of photons by atoms, leading to a change in their wavelength.

Reflection of light from a metal surface without any change in energy.

Correct Answer: A

Solution:

The photoelectric effect involves the emission of electrons from a metal surface when it is exposed to light of a frequency above a certain threshold, demonstrating the particle nature of light.

Chapter Concept:

Electromagnetic Radiation and Quantum Theory

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: B

Solution:

The Balmer series corresponds to the transitions of electrons from higher energy levels to the second energy level (n=2) in the hydrogen atom.

Chapter Concept:

Atomic Spectra

It supports the idea of electrons in fixed orbits.

It contradicts the idea of electrons having well-defined orbits.

It suggests that electrons do not exist.

It has no effect on the Bohr model.

Correct Answer: B

Solution:

The Heisenberg uncertainty principle contradicts the Bohr model's assumption of electrons having well-defined orbits because it is impossible to know both the position and velocity of an electron precisely.

Chapter Concept:

Heisenberg Uncertainty Principle

^{34}_{16}S^{2-}

^{34}_{16}S^{+}

^{34}_{16}S^{2+}

^{34}_{16}S^{-}

Correct Answer: A

Solution:

The element with atomic number 16 is sulfur (

S

). To be isoelectronic with argon (

Ar

), which has 18 electrons, sulfur must gain 2 electrons, forming the ion

^{34}_{16}S^{2-}

Chapter Concept:

Atomic and Ionic Symbols

It supports the idea of fixed electron orbits.

It contradicts the idea of fixed electron orbits.

It explains the stability of electron orbits.

It is irrelevant to the Bohr model.

Correct Answer: B

Solution:

The Heisenberg uncertainty principle contradicts the idea of fixed electron orbits in the Bohr model because it states that the exact position and velocity of an electron cannot be known simultaneously.

Chapter Concept:

Electromagnetic Radiation and Quantum Theory

^{31}_{15}P^{3-}

^{31}_{15}P^{3+}

^{31}_{15}P^{-}

^{31}_{15}P^{+}

Correct Answer: A

Solution:

The atomic number (15) indicates the number of protons, which is equal to the number of electrons in a neutral atom. The mass number (31) indicates the sum of protons and neutrons. For a 3- charge, the atom has gained 3 electrons, making the ionic symbol

^{31}_{15}P^{3-}

Chapter Concept:

Atomic and Ionic Symbols

It describes the motion of macroscopic objects.

It provides the possible energy states and wave functions of electrons.

It explains the photoelectric effect.

It describes the distribution of protons in the nucleus.

Correct Answer: B

Solution:

The Schrödinger equation, when solved for the hydrogen atom, provides the possible energy states the electron can occupy and the corresponding wave functions, which are characterized by quantum numbers.

Chapter Concept:

Quantum Mechanical Model

It supports the notion of fixed electron orbits.

It contradicts the idea of electrons having precise orbits with known velocities and positions.

It confirms the stability of electron orbits.

It suggests that electrons are stationary within the atom.

Correct Answer: B

Solution:

The Heisenberg uncertainty principle states that it is impossible to know both the exact position and velocity of an electron simultaneously, which contradicts the Bohr model's assumption of defined electron orbits.

Chapter Concept:

Electromagnetic Radiation and Quantum Theory

Structure of Atom

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CBSE Learning Objectives – Key Concepts & Skills You Must Know

Learning Objectives

CBSE Revision Notes & Quick Summary for Last-Minute Study

Chapter Notes

Electronic Configurations

Atomic Models

Quantum Mechanical Model

Electromagnetic Radiation and Quantum Theory

Atomic Spectra

Electron Configuration Principles

Photoelectric Effect

De Broglie Wavelength and Matter Waves

Heisenberg Uncertainty Principle

Atomic and Ionic Symbols

CBSE Exam Tips, Important Questions & Common Mistakes to Avoid

Common Mistakes & Exam Tips

Electronic Configurations

Atomic Models

Quantum Mechanical Model

Electromagnetic Radiation and Quantum Theory

Atomic Spectra

Electron Configuration Principles

Photoelectric Effect

De Broglie Wavelength and Matter Waves

Heisenberg Uncertainty Principle

Atomic and Ionic Symbols

Multiple Choice Questions

Q1.In the context of electromagnetic radiation, what is the significance of the wave-particle duality?

Correct Answer: B

Q2.Consider a particle with a mass twice that of an electron moving with the same velocity as the electron in the previous question. What would be the de Broglie wavelength of this particle?

Correct Answer: A

Q3.Consider an electron confined in a one-dimensional box of length LLL. According to the Heisenberg uncertainty principle, if the uncertainty in the position of the electron is reduced to L10\frac{L}{10}10L​, what can be said about the uncertainty in its momentum?

Correct Answer: A

Q4.In the context of electronic configurations, what is the significance of the quantum number lll?

Correct Answer: B

Q5.How many unpaired electrons are present in the ground state electronic configuration of oxygen?

Correct Answer: C

Q6.According to Bohr's model, how do electrons move around the nucleus?

Correct Answer: B

Q7.What was a major limitation of Rutherford's atomic model?

Correct Answer: A

Q8.Which of the following quantum numbers is NOT part of the quantum mechanical model of the atom?

Correct Answer: D

Q9.If the threshold frequency for a metal is 5×10145 \times 10^{14}5×1014 Hz, what happens when light of frequency 4×10144 \times 10^{14}4×1014 Hz is shone on the metal?

Correct Answer: C

Correct Answer: C

Q11.An element has the following electron configuration: [Ar]3d104s24p5[Ar] 3d^{10} 4s^2 4p^5[Ar]3d104s24p5. Which principle is violated if an electron is added to the 4s4s4s orbital before the 4p4p4p orbital is fully filled?

Correct Answer: A

Q12.What is the primary feature of Planck's quantum theory?

Correct Answer: A

Correct Answer: B

Q14.In Bohr's model of the atom, what determines the energy level of an electron?

Correct Answer: A

Q15.Which of the following configurations represents an atom that violates the Pauli exclusion principle?

Correct Answer: D

Q16.Which atomic model first introduced the concept of a nucleus at the center of the atom?

Correct Answer: B

Q17.Which phenomenon is explained by the photoelectric effect?

Correct Answer: A

Q18.Consider an atom with the electronic configuration 1s22s22p63s23p51s^2 2s^2 2p^6 3s^2 3p^51s22s22p63s23p5. According to Hund's rule, what is the expected magnetic property of this atom?

Correct Answer: B

Q19.Which principle states that no two electrons in an atom can have the same set of four quantum numbers?

Correct Answer: B

Q20.According to de Broglie's hypothesis, what property of matter is associated with wave-particle duality?

Correct Answer: C

Q21.Which of the following electronic configurations represents an exception to the Aufbau principle?

Correct Answer: B

Q22.According to Planck's quantum theory, which statement is true about energy quantization?

Correct Answer: B

Correct Answer: A

Q24.What does the Heisenberg uncertainty principle state about the measurement of certain pairs of physical properties, such as position and momentum?

Correct Answer: B

Q25.What is the electronic configuration of an element with atomic number 29, and what does this configuration imply about its chemical properties?

Correct Answer: A

Q26.According to the quantum mechanical model, what determines the energy of an electron in a multi-electron atom?

Correct Answer: C

Q27.What is the primary limitation of the Bohr model of the atom?

Correct Answer: B