Atoms

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Summary

Chapter Twelve: Atoms

Summary

Atom is electrically neutral, containing equal amounts of positive and negative charges.
Thomson's model describes the atom as a spherical cloud of positive charges with electrons embedded.
Rutherford's model posits that most mass and positive charge are concentrated in a tiny nucleus, with electrons revolving around it.
Rutherford's model has two main difficulties:
- Predicts atomic instability due to accelerated electrons spiraling into the nucleus.
- Cannot explain the characteristic line spectra of different elements.
Atoms emit a characteristic spectrum consisting of isolated parallel lines, known as line spectrum, providing information about atomic structure.
Bohr's model for hydrogenic atoms introduces three postulates:
1. Electrons revolve in stable orbits without emitting energy.
2. Angular momentum is quantized: L = nh/2π (n is an integer).
3. Electrons can transition between orbits, emitting or absorbing photons with energy equal to the difference between states.
The total energy of an electron in a hydrogen atom is quantized: Eₙ = -13.6 eV/n², with n = 1 being the ground state.
Higher energy states (n > 1) are excited by collisions or photon absorption.
Bohr's model is limited to hydrogenic atoms and does not apply to multi-electron atoms.

Important Points

Both Thomson's and Rutherford's models are unstable systems.
Bohr's model laid the foundation for quantum mechanics but is not entirely accurate; it has been replaced by more comprehensive theories.
The frequency of emitted spectral lines is related to the energy difference between orbits, not the frequency of electron revolution.
Bohr's model remains useful despite its limitations due to its foundational role in quantum theory.

Learning Objectives

Understand the historical development of atomic theory.
Explain the significance of J. J. Thomson's experiments in the context of atomic structure.
Describe the differences between Thomson's and Rutherford's models of the atom.
Analyze the limitations of Rutherford's model in explaining atomic stability and spectra.
Summarize Bohr's model of the hydrogen atom and its postulates.
Apply Bohr's quantization condition to calculate energy levels and transitions in hydrogenic atoms.
Discuss the implications of de Broglie's hypothesis on the wave nature of electrons.
Evaluate the applicability of Bohr's model to multi-electron atoms and its limitations.

Detailed Notes

Chapter Twelve: Atoms

12.1 Introduction

By the nineteenth century, evidence supported the atomic hypothesis of matter.
In 1897, J. J. Thomson discovered that atoms contain negatively charged electrons, making them electrically neutral overall.
Thomson's model (1898): Positive charge is uniformly distributed, with electrons embedded like seeds in a watermelon (plum pudding model).
Subsequent studies revealed a different arrangement of charges.

12.2 Key Models of the Atom

Thomson's Model

Atom as a spherical cloud of positive charges with electrons embedded.

Rutherford's Model

Most mass and positive charge concentrated in a tiny nucleus.
Electrons revolve around the nucleus.
Issues with Rutherford's model:
- Predicts instability due to spiraling electrons.
- Cannot explain characteristic line spectra of different elements.

Bohr's Model

Proposed to explain line spectra and stability of hydrogenic atoms.
Introduced three postulates:
1. Electrons revolve in stable orbits without emitting energy.
2. Angular momentum is quantized: L = nh/2π (n = principal quantum number).
3. Electrons can transition between orbits, emitting or absorbing photons.
Total energy quantized: Eₙ = -13.6 eV/n².
Ground state energy of hydrogen atom is -13.6 eV.

12.3 De Broglie's Explanation

De Broglie proposed that electrons have wave properties, explaining Bohr's quantization of angular momentum.
Standing waves form in electron orbits, leading to quantized energy levels.

12.4 Limitations of Bohr's Model

Applicable only to hydrogenic atoms; fails for multi-electron atoms.
Cannot explain relative intensities of spectral lines.

12.5 Summary of Key Points

Atoms are electrically neutral, containing equal positive and negative charges.
Thomson's model depicts a cloud of positive charge with embedded electrons.
Rutherford's model has a nucleus with electrons revolving around it.
Bohr's model introduces quantized orbits and energy levels for hydrogenic atoms.
The wave nature of electrons explains quantization in Bohr's model.
Bohr's model has limitations and is replaced by quantum mechanics for complex atoms.

Exam Tips & Common Mistakes

Common Mistakes and Exam Tips

Common Pitfalls

Misunderstanding Atomic Models: Students often confuse the characteristics of Thomson's and Rutherford's models. Remember that Thomson's model depicts a uniform distribution of positive charge with electrons embedded, while Rutherford's model has a dense nucleus with electrons orbiting around it.
Ignoring Stability Issues: Many overlook the instability predicted by both Thomson's and Rutherford's models. Thomson's model is electrostatically unstable, and Rutherford's model predicts that electrons should spiral into the nucleus due to electromagnetic radiation.
Confusing Quantum Numbers: Be careful not to confuse the principal quantum number (n) with other quantum numbers. Only the principal quantum number determines the energy levels in Bohr's model.

Exam Tips

Focus on Key Postulates: When studying Bohr's model, emphasize the three postulates: stable orbits without energy emission, quantized angular momentum, and energy transitions leading to photon emission.
Understand Energy Levels: Be clear on how energy levels are quantized in hydrogen atoms, specifically that the ground state energy is -13.6 eV and how higher states correspond to larger values of n.
Practice Problems: Work through problems involving energy transitions and spectral lines, as these are common exam questions. Familiarize yourself with calculations involving the frequency and wavelength of emitted photons during transitions.

Practice & Assessment

Multiple Choice Questions

Electrons orbit the nucleus like planets around the sun.

Electrons are embedded in a uniform sphere of positive charge.

Electrons are located in distinct energy levels.

Electrons are concentrated in the nucleus.

Correct Answer: B

Solution:

In J. J. Thomson's plum pudding model, electrons are embedded in a uniform sphere of positive charge, similar to seeds in a watermelon.

Mass and positive charge are uniformly distributed throughout the atom.

Mass is concentrated in the nucleus, while electrons revolve around it.

Electrons are stationary within a positively charged sphere.

Mass is evenly distributed between electrons and the nucleus.

Correct Answer: B

Solution:

Rutherford's model posits that the entire positive charge and most of the mass of the atom are concentrated in a small volume called the nucleus, with electrons revolving around it.

Ernst Rutherford

Johann Jakob Balmer

J. J. Thomson

Niels Bohr

Correct Answer: B

Solution:

Johann Jakob Balmer obtained a simple empirical formula for the wavelengths of lines emitted by atomic hydrogen, known as the Balmer series.

To discover electrons

To investigate the atomic structure

To measure the speed of light

To study electromagnetic waves

Correct Answer: B

Solution:

The alpha-particle scattering experiment by Geiger and Marsden aimed to investigate the atomic structure, leading to the proposal of Rutherford's nuclear model.

Thomson's plum pudding model

Rutherford's nuclear model

Bohr's model

Quantum mechanical model

Correct Answer: A

Solution:

Thomson's plum pudding model proposed that the positive charge is spread throughout the atom, with electrons embedded within it, similar to seeds in a watermelon.

Balmer series

Paschen series

Lyman series

Brackett series

Correct Answer: C

Solution:

The Lyman series is associated with the ultraviolet region, as indicated by the wavelengths 91 nm and 122 nm.

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: C

Solution:

The Paschen series corresponds to the infrared region, as indicated by the wavelengths associated with it.

It did not account for the presence of electrons

It suggested a continuous spectrum instead of discrete wavelengths

It incorrectly described the nucleus as positively charged

It was based on incorrect experimental data

Correct Answer: B

Solution:

Rutherford's model could not explain why atoms emit light of only discrete wavelengths, as it suggested a continuous spectrum due to the classical picture of electrons revolving around the nucleus.

Atoms are indivisible particles.

Electrons orbit the nucleus in fixed paths.

The atom's positive charge is concentrated in a small nucleus.

Electrons are embedded in a positive sphere.

Correct Answer: C

Solution:

Rutherford's gold foil experiment led to the conclusion that the positive charge and most of the atom's mass are concentrated in a small nucleus.

Electrons are embedded in a positively charged sphere.

Electrons orbit the nucleus like planets around the sun.

Electrons are located in fixed orbits with quantized energy levels.

Electrons are randomly distributed outside the nucleus.

Correct Answer: A

Solution:

In J. J. Thomson's model, the atom is described as a positively charged sphere with electrons embedded within it, similar to seeds in a watermelon.

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: B

Solution:

The Balmer series is visible in the visible spectrum, as indicated by the labeled wavelengths of 365 nm and 656 nm in the diagram.

Electron

Neutron

Nucleus

Photon

Correct Answer: C

Solution:

Ernst Rutherford's experiments on alpha-particle scattering led to the discovery of the atomic nucleus.

The Lyman series is visible in the visible spectrum.

The Balmer series is found in the ultraviolet region.

The Paschen series corresponds to the infrared region.

The Brackett series is visible in the ultraviolet region.

Correct Answer: C

Solution:

The Paschen series corresponds to the infrared region, while the Lyman series is in the ultraviolet and the Balmer series is in the visible spectrum.

Continuous spectrum

Discrete wavelengths

Higher intensity

Lower frequency

Correct Answer: B

Solution:

Light emitted by rarefied gases has discrete wavelengths, appearing as a series of bright lines, unlike the continuous spectrum of dense gases.

Plum pudding model

Rutherford model

Bohr model

Quantum mechanical model

Correct Answer: A

Solution:

The plum pudding model, proposed by J. J. Thomson, describes the atom as a sphere of positive charge with electrons embedded in it.

J. J. Thomson

Johann Jakob Balmer

Hans Geiger and Ernst Marsden

Niels Bohr

Correct Answer: C

Solution:

Hans Geiger and Ernst Marsden performed the experiment under the suggestion of Ernst Rutherford.

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: B

Solution:

The Balmer series corresponds to the visible spectrum, with wavelengths such as 365 nm and 656 nm.

Lyman series

Balmer series

Paschen series

Rydberg series

Correct Answer: B

Solution:

The Balmer series is part of the hydrogen emission spectrum and is visible in the visible spectrum.

Continuous spectrum

Discrete wavelengths

Infrared spectrum

Ultraviolet spectrum

Correct Answer: B

Solution:

Light emitted from rarefied gases when excited electrically has only certain discrete wavelengths.

The atoms in rarefied gases are isolated, leading to emission at specific wavelengths.

Rarefied gases have high atomic density, causing continuous spectra.

The interaction between atoms in rarefied gases causes discrete wavelengths.

Rarefied gases absorb light at all wavelengths, emitting discrete ones.

Correct Answer: A

Solution:

In rarefied gases, the average spacing between atoms is large, so the radiation emitted can be considered due to individual atoms rather than interactions between atoms or molecules. This results in emission at discrete wavelengths.

J. J. Thomson

Niels Bohr

Ernst Rutherford

Albert Einstein

Correct Answer: C

Solution:

Ernst Rutherford proposed the classic experiment of scattering alpha particles, which led to the discovery of the atomic nucleus.

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: C

Solution:

The Paschen series of the hydrogen emission spectrum is visible in the infrared region.

J. J. Thomson

Ernst Rutherford

Niels Bohr

Albert Einstein

Correct Answer: B

Solution:

Ernst Rutherford is credited with the discovery of alpha-rays and beta-rays.

The cathode ray tube experiment.

The gold foil experiment.

The oil drop experiment.

The photoelectric effect experiment.

Correct Answer: B

Solution:

The gold foil experiment, conducted by Geiger and Marsden under Rutherford's guidance, led to the discovery of the atomic nucleus.

Atoms contain a nucleus.

Atoms contain negatively charged electrons.

Atoms emit a continuous spectrum.

Atoms are indivisible.

Correct Answer: B

Solution:

J. J. Thomson's experiments revealed that atoms contain negatively charged constituents called electrons.

Discovery of the electron

Discovery of the atomic nucleus

Discovery of the neutron

Discovery of isotopes

Correct Answer: B

Solution:

Geiger and Marsden's experiments led to the discovery of the atomic nucleus, as they observed that a small fraction of alpha particles were deflected at large angles, indicating a concentrated positive charge.

The wavelengths of the Balmer series fall within the range of visible light.

The Balmer series involves transitions to the ground state.

The Balmer series is emitted by rarefied gases under high pressure.

The Balmer series is the result of electron transitions from the first excited state.

Correct Answer: A

Solution:

The Balmer series is visible because its wavelengths fall within the range of visible light, as indicated by the specific wavelengths such as 365 nm and 656 nm.

J. J. Thomson

Ernst Rutherford

Johann Jakob Balmer

Hans Geiger

Correct Answer: A

Solution:

J. J. Thomson's experiments on electric discharge through gases revealed the presence of electrons in atoms.

It is visible in the ultraviolet region.

It is associated with the infrared region.

It is visible in the visible spectrum.

It is not associated with any specific region.

Correct Answer: C

Solution:

The Balmer series is visible in the visible spectrum, as indicated by the specific wavelengths associated with it.

Balmer series

Lyman series

Paschen series

Rydberg series

Correct Answer: B

Solution:

The Lyman series is found in the ultraviolet region of the hydrogen spectrum.

Balmer series

Lyman series

Paschen series

Brackett series

Correct Answer: B

Solution:

The Lyman series corresponds to the ultraviolet region of the hydrogen emission spectrum.

Mass is evenly distributed throughout the atom.

Mass is concentrated in the electrons.

Mass is concentrated in the nucleus.

Mass is concentrated in the electron cloud.

Correct Answer: C

Solution:

Rutherford's model suggests that most of the atom's mass is concentrated in a small volume called the nucleus.

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: C

Solution:

The Paschen series corresponds to the infrared region in the emission spectrum of hydrogen.

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: B

Solution:

The Balmer series is associated with the visible spectrum for hydrogen.

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: B

Solution:

The Balmer series corresponds to the visible region of the hydrogen emission spectrum.

It could not explain the discrete wavelengths of light emitted by atoms.

It did not account for the electron's charge.

It suggested that atoms were indivisible.

It proposed that electrons were stationary.

Correct Answer: A

Solution:

Rutherford's nuclear model could not explain why atoms emit light at only certain discrete wavelengths, which was a significant limitation.

Positive charge is uniformly distributed throughout the atom, with electrons embedded like seeds in a watermelon.

Electrons orbit a central positive nucleus, similar to planets orbiting the sun.

Electrons are concentrated at the center, with positive charge surrounding them.

Positive and negative charges are separated by a fixed distance within the atom.

Correct Answer: A

Solution:

In J. J. Thomson's plum pudding model, the positive charge is uniformly distributed throughout the atom, and electrons are embedded within it, similar to seeds in a watermelon.

Scattering of alpha particles by metal foils

Electric discharge through gases

Discovery of radioactivity

Measurement of atomic spectra

Correct Answer: A

Solution:

Rutherford's nuclear model was proposed based on the results of the alpha-particle scattering experiment performed by Hans Geiger and Ernst Marsden under Rutherford's guidance.

Dense gases emit a continuous spectrum, while rarefied gases emit discrete spectral lines.

Both dense and rarefied gases emit continuous spectra.

Dense gases emit discrete spectral lines, while rarefied gases emit a continuous spectrum.

Both dense and rarefied gases emit discrete spectral lines.

Correct Answer: A

Solution:

Dense gases emit a continuous spectrum due to interactions between atoms or molecules, whereas rarefied gases emit discrete spectral lines due to individual atomic emissions.

Atoms are indivisible and solid.

Electrons are embedded in a positive sphere.

Atoms have a small, dense nucleus.

Electrons move in fixed paths around the nucleus.

Correct Answer: C

Solution:

The alpha-particle scattering experiment led to the conclusion that atoms have a small, dense nucleus.

The discovery of the neutron.

The observation of discrete spectral lines in hydrogen.

The scattering of alpha particles by a thin gold foil.

The discovery of isotopes.

Correct Answer: C

Solution:

The scattering of alpha particles by a thin gold foil, as observed by Geiger and Marsden, led to the rejection of Thomson's plum pudding model and the development of Rutherford's nuclear model.

It is visible in the infrared region.

It is visible in the ultraviolet region.

It is visible in the visible spectrum.

It is visible in the X-ray region.

Correct Answer: C

Solution:

The Balmer series is visible in the visible spectrum, as indicated by wavelengths such as 365 nm and 656 nm.

Ernst Rutherford

Niels Bohr

J. J. Thomson

Albert Einstein

Correct Answer: C

Solution:

J. J. Thomson proposed the plum pudding model of the atom in 1898.

Continuous spectrum

Discrete wavelengths

Infrared radiation

Ultraviolet radiation

Correct Answer: B

Solution:

Rarefied gases emit radiation at discrete wavelengths, appearing as a series of bright lines, when excited electrically.

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: C

Solution:

The Paschen series corresponds to the infrared region of the hydrogen spectrum.

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: B

Solution:

The Balmer series corresponds to electron transitions in hydrogen that emit light in the visible region of the electromagnetic spectrum.

Evenly distributed throughout the atom

In the electrons

In the nucleus

In the outer shells

Correct Answer: C

Solution:

In Rutherford's nuclear model, most of the atom's mass is concentrated in the nucleus.

Atoms contain a dense nucleus

Atoms have negatively charged constituents called electrons

Atoms are indivisible particles

Atoms emit continuous spectra

Correct Answer: B

Solution:

J. J. Thomson's experiments revealed that atoms contain negatively charged constituents, known as electrons, which are identical for all atoms.

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: B

Solution:

The Balmer series is associated with the visible region of the electromagnetic spectrum, as indicated by the wavelengths such as 365 nm and 656 nm.

The continuous motion of electrons around the nucleus

The quantized energy levels of electrons

The uniform distribution of positive charge

The interaction between atoms in a dense gas

Correct Answer: B

Solution:

Rutherford's model could not explain discrete wavelengths, but later models showed that the quantized energy levels of electrons are responsible for discrete spectral lines.

The positive charge is uniformly distributed throughout the atom.

The positive charge and most of the mass are concentrated in a small nucleus.

Electrons are embedded in a sphere of positive charge.

Electrons revolve around the nucleus in fixed orbits without any energy loss.

Correct Answer: B

Solution:

Rutherford's nuclear model proposed that the positive charge and most of the mass of the atom are concentrated in a small region called the nucleus, with electrons revolving around it.

Cathode ray tube experiment

Alpha-particle scattering experiment

Oil drop experiment

Photoelectric effect experiment

Correct Answer: B

Solution:

The alpha-particle scattering experiment led to the proposal of Rutherford's nuclear model of the atom.

To confirm the plum pudding model of the atom.

To measure the charge of an electron.

To investigate the atomic structure and discover the nucleus.

To study the emission spectra of hydrogen.

Correct Answer: C

Solution:

The alpha-particle scattering experiment aimed to investigate the atomic structure, leading to the discovery of the nucleus and the proposal of Rutherford's nuclear model of the atom.

Thomson's cathode ray experiment

Rutherford's alpha-particle scattering experiment

Bohr's hydrogen spectrum experiment

Einstein's photoelectric effect experiment

Correct Answer: B

Solution:

Rutherford's alpha-particle scattering experiment led to the discovery of the atomic nucleus.

656 nm

820 nm

91 nm

1875 nm

Correct Answer: C

Solution:

The Lyman series includes wavelengths such as 91 nm, which are in the ultraviolet region.

Atoms are mostly empty space with a dense nucleus.

Electrons are evenly distributed throughout the atom.

Atoms consist of a solid positive sphere.

Electrons are stationary within the atom.

Correct Answer: A

Solution:

Rutherford's experiment concluded that atoms are mostly empty space with a dense nucleus at the center.

Electrons are embedded in a positively charged sphere.

Electrons orbit around a central nucleus.

Electrons are scattered randomly around the atom.

Electrons are fixed at specific energy levels.

Correct Answer: A

Solution:

The plum pudding model suggests that electrons are embedded in a positively charged sphere, similar to seeds in a watermelon.

Plum pudding model

Planetary model

Bohr model

Quantum mechanical model

Correct Answer: A

Solution:

J. J. Thomson proposed the plum pudding model of the atom in 1898, where the positive charge is uniformly distributed and electrons are embedded like seeds in a watermelon.

Rutherford's nuclear model

Bohr's model

Thomson's plum pudding model

Quantum mechanical model

Correct Answer: C

Solution:

J. J. Thomson proposed the plum pudding model in 1898, where he suggested that electrons are embedded within a positively charged sphere.

They indicate the presence of isotopes.

They are due to interactions between atoms.

They are characteristic of individual atoms.

They result from thermal vibrations.

Correct Answer: C

Solution:

Discrete wavelengths in the emission spectra of rarefied gases are characteristic of individual atoms, as the average spacing between atoms is large, minimizing interactions.

J. J. Thomson

Ernst Rutherford

Hans Geiger and Ernst Marsden

Niels Bohr

Correct Answer: C

Solution:

Hans Geiger and Ernst Marsden conducted the experiment under the suggestion of Ernst Rutherford, leading to the discovery of the atomic nucleus.

In the electron cloud surrounding the nucleus.

Uniformly distributed throughout the atom.

In the nucleus at the center of the atom.

In the outer orbits of the atom.

Correct Answer: C

Solution:

Rutherford's nuclear model states that the majority of the atom's mass is concentrated in the nucleus at the center of the atom.

J. J. Thomson

Ernst Rutherford

Niels Bohr

James Chadwick

Correct Answer: A

Solution:

J. J. Thomson proposed the plum pudding model of the atom in 1898, where the positive charge is uniformly distributed, and electrons are embedded like seeds in a watermelon.

Balmer series

Paschen series

Lyman series

Brackett series

Correct Answer: C

Solution:

The Lyman series corresponds to the ultraviolet region in the hydrogen emission spectrum.

Discovered the electron

Proposed the nuclear model

Developed a formula for hydrogen spectral lines

Identified alpha and beta rays

Correct Answer: C

Solution:

Johann Jakob Balmer developed a simple empirical formula for the wavelengths of a group of lines emitted by atomic hydrogen.

Balmer series

Paschen series

Lyman series

Brackett series

Correct Answer: C

Solution:

The Lyman series of the hydrogen emission spectrum is visible in the ultraviolet region, as indicated by wavelengths such as 91 nm and 122 nm.

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: B

Solution:

The Balmer series corresponds to electron transitions that end at the second energy level in the hydrogen atom.

Continuous spectrum

Discrete spectrum

Absorption spectrum

Blackbody spectrum

Correct Answer: B

Solution:

Rarefied gases emit a discrete spectrum of bright lines when excited electrically.

It is in the ultraviolet region.

It is in the visible spectrum.

It is in the infrared region.

It corresponds to X-ray emissions.

Correct Answer: B

Solution:

The Balmer series is associated with the visible spectrum of hydrogen.

Plum pudding model

Nuclear model

Planetary model

Quantum model

Correct Answer: A

Solution:

J. J. Thomson proposed the plum pudding model, where electrons are embedded in a positively charged 'pudding'.

It could not explain the stability of the atom.

It could not account for the existence of isotopes.

It failed to explain the discrete wavelengths of spectral lines.

It did not consider the electron's wave nature.

Correct Answer: C

Solution:

Rutherford's nuclear model could not explain why atoms emit light of only discrete wavelengths, a limitation that was later addressed by quantum mechanics.

The discovery of electron charge

The scattering of alpha particles by metal foils

The observation of spectral lines

The discovery of isotopes

Correct Answer: B

Solution:

Rutherford's nuclear model was proposed based on the experimental evidence from the scattering of alpha particles by metal foils, which indicated a concentrated positive charge in the nucleus.

Continuous spectrum

Discrete wavelengths

Infrared radiation

Ultraviolet radiation

Correct Answer: B

Solution:

Rarefied gases emit light with discrete wavelengths, appearing as a series of bright lines.

Lyman series

Balmer series

Paschen series

Brackett series

Correct Answer: B

Solution:

The Balmer series is associated with the visible spectrum.

J. J. Thomson

Niels Bohr

Ernst Rutherford

Albert Einstein

Correct Answer: C

Solution:

Ernst Rutherford is credited with discovering the atomic nucleus through his alpha particle scattering experiments.

Transition from

n=3

n=2

Transition from

n=2

n=1

Transition from

n=4

n=3

Transition from

n=5

n=4

Correct Answer: B

Solution:

The transition from

n=2

n=1

corresponds to the Lyman series, which is in the ultraviolet region.

The positive charge is concentrated in the nucleus, with electrons orbiting around it.

Electrons are embedded in a positively charged sphere, similar to seeds in a watermelon.

Atoms consist of a dense nucleus with electrons in fixed orbits.

Electrons move in elliptical orbits around a central positive charge.

Correct Answer: B

Solution:

J. J. Thomson's plum pudding model describes the atom as a positively charged sphere with electrons embedded within it, similar to seeds in a watermelon.

The existence of electrons

The discrete wavelengths of light emitted by atoms

The presence of protons

The mass of the atom

Correct Answer: B

Solution:

Rutherford's model could not explain why atoms emit light of only discrete wavelengths.

True or False

Correct Answer: False

Solution:

Rutherford's nuclear model could not explain the emission of light in discrete wavelengths, which was a limitation of the model.

Correct Answer: True

Solution:

It was established in the early nineteenth century that each element has a characteristic spectrum of radiation.

Correct Answer: False

Solution:

Light emitted from rarefied gases consists of discrete wavelengths, appearing as a series of bright lines.

Correct Answer: False

Solution:

Rutherford's nuclear model could not explain why atoms emit light of only discrete wavelengths.

Correct Answer: False

Solution:

The Lyman series is positioned in the ultraviolet region, not the infrared region.

Correct Answer: True

Solution:

Rutherford's experiments, particularly the scattering of alpha particles, led to the discovery of the atomic nucleus.

Correct Answer: False

Solution:

In the plum pudding model, the positive charge is uniformly distributed throughout the atom, not concentrated in a nucleus.

Correct Answer: False

Solution:

Light emitted from rarefied gases appears as a series of bright lines, not a continuous spectrum.

Correct Answer: True

Solution:

J. J. Thomson discovered electrons as negatively charged constituents of atoms through his experiments with electric discharge in gases.

Correct Answer: True

Solution:

The Lyman series of hydrogen's emission spectrum is indeed observed in the ultraviolet region.

Correct Answer: True

Solution:

Rutherford's model describes electrons orbiting the nucleus in a manner analogous to planets orbiting the sun.

Correct Answer: False

Solution:

The Lyman series is located in the ultraviolet region of the spectrum.

Correct Answer: True

Solution:

According to J. J. Thomson's model, the positive charge of the atom is uniformly distributed throughout the volume of the atom, with electrons embedded in it.

Correct Answer: True

Solution:

According to J. J. Thomson's plum pudding model, the positive charge is spread uniformly throughout the atom, with electrons embedded like seeds in a watermelon.

Correct Answer: True

Solution:

Rutherford's nuclear model proposed that electrons revolve around a central nucleus, much like planets orbit the sun.

Correct Answer: True

Solution:

Rutherford's model failed to explain the discrete wavelengths of light emitted by atoms, which was a limitation of the model.

Correct Answer: True

Solution:

J. J. Thomson's experiments on electric discharge through gases showed that atoms contain negatively charged electrons that are identical for all atoms.

Correct Answer: True

Solution:

J. J. Thomson's experiments on electric discharge through gases revealed that all atoms contain identical negatively charged constituents known as electrons.

Correct Answer: False

Solution:

The Balmer series of hydrogen is located in the visible spectrum, not the infrared region.

Correct Answer: True

Solution:

Rutherford discovered the atomic nucleus by analyzing the results of alpha-particle scattering experiments.

Correct Answer: False

Solution:

The emission spectrum of rarefied gases heated in a flame consists of discrete wavelengths, appearing as a series of bright lines.

Correct Answer: True

Solution:

Rutherford's model proposed that the atom's positive charge and most of its mass are concentrated in a small central nucleus, with electrons orbiting around it.

Correct Answer: False

Solution:

Light emitted from rarefied gases heated in a flame has only certain discrete wavelengths, appearing as a series of bright lines.

Correct Answer: False

Solution:

In J. J. Thomson's plum pudding model, the positive charge is uniformly distributed throughout the atom, not concentrated in a nucleus.

Correct Answer: True

Solution:

Rutherford's model suggested that electrons revolve around a central nucleus, similar to planets orbiting the sun.

Correct Answer: True

Solution:

In rarefied gases, the average spacing between atoms is large, so the radiation emitted can be considered due to individual atoms.

Correct Answer: True

Solution:

J. J. Thomson's experiments on electric discharge through gases showed that atoms of different elements contain electrons, which are negatively charged.

Correct Answer: True

Solution:

Each element has a characteristic spectrum of radiation, with hydrogen always giving a set of lines with fixed relative positions.

Correct Answer: True

Solution:

Rutherford's alpha-particle scattering experiments led to the discovery of the atomic nucleus.

Correct Answer: False

Solution:

The Balmer series is visible in the visible spectrum, not the ultraviolet region.

Correct Answer: True

Solution:

J. J. Thomson's plum pudding model depicted the atom as having electrons embedded like seeds in a watermelon within a positively charged 'pudding'.

Correct Answer: True

Solution:

Rarefied gases emit light at discrete wavelengths, resulting in a spectrum of bright lines, unlike the continuous spectrum from condensed matter.

Correct Answer: False

Solution:

J. J. Thomson's plum pudding model proposed that the positive charge is uniformly distributed throughout the atom, not concentrated in a nucleus.

Correct Answer: False

Solution:

Rutherford's nuclear model proposed that the entire positive charge and most of the mass of the atom are concentrated in a small volume called the nucleus.

Correct Answer: True

Solution:

In 1885, Johann Jakob Balmer obtained a simple empirical formula that gave the wavelengths of a group of lines emitted by atomic hydrogen.

Correct Answer: True

Solution:

The Paschen series is part of hydrogen's emission spectrum and is observed in the infrared region.

Correct Answer: True

Solution:

In rarefied gases, the average spacing between atoms is large, leading to the emission of light at discrete wavelengths, appearing as bright lines.

Correct Answer: True

Solution:

Rutherford's experiments with alpha-particle scattering led to the discovery of the atomic nucleus.

Correct Answer: False

Solution:

The Paschen series is associated with the infrared region, not the ultraviolet region.

Correct Answer: True

Solution:

It was established that each element has a unique spectrum of radiation, which is characteristic of that element.

Correct Answer: True

Solution:

Rutherford's nuclear model proposes that the entire positive charge and most of the mass of the atom is concentrated in the nucleus, with electrons revolving around it.

Correct Answer: True

Solution:

Rutherford's experiments with alpha-particle scattering led to the discovery of the atomic nucleus, where he proposed that the positive charge and most of the mass of the atom are concentrated.

Correct Answer: False

Solution:

J. J. Thomson's model, known as the plum pudding model, proposed that the positive charge is uniformly distributed throughout the atom, not concentrated in the nucleus.

Correct Answer: True

Solution:

Rarefied gases emit light at certain discrete wavelengths, resulting in a spectrum that appears as a series of bright lines.

Correct Answer: True

Solution:

Light emitted from rarefied gases has discrete wavelengths, appearing as a series of bright lines due to individual atoms.

Correct Answer: False

Solution:

In rarefied gases, the light emitted appears as a series of bright lines, not a continuous spectrum.

Correct Answer: False

Solution:

The Balmer series is visible in the visible spectrum, not the ultraviolet region.

Correct Answer: True

Solution:

In rarefied gases, the average spacing between atoms is large, allowing individual atoms to emit radiation, resulting in discrete bright lines.

Correct Answer: True

Solution:

The scattering experiments conducted by Geiger and Marsden under Rutherford's guidance led to the discovery of the atomic nucleus.

Correct Answer: False

Solution:

In the plum pudding model, the positive charge is uniformly distributed throughout the volume of the atom, not concentrated in a nucleus.

Atoms

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Summary

Chapter Twelve: Atoms

Summary

Important Points

Learning Objectives

Detailed Notes

Chapter Twelve: Atoms

12.1 Introduction

12.2 Key Models of the Atom

Thomson's Model

Rutherford's Model

Bohr's Model

12.3 De Broglie's Explanation

12.4 Limitations of Bohr's Model

12.5 Summary of Key Points

Exam Tips & Common Mistakes

Common Mistakes and Exam Tips

Common Pitfalls

Exam Tips

Practice & Assessment

Multiple Choice Questions

Q1.According to the plum pudding model proposed by J. J. Thomson, how are electrons arranged in an atom?

Correct Answer: B

Q2.According to Rutherford's nuclear model of the atom, which of the following is true about the distribution of mass and charge?

Correct Answer: B

Q3.Which physicist is credited with obtaining a simple empirical formula for the wavelengths of lines emitted by atomic hydrogen?

Correct Answer: B

Q4.What was the primary objective of the alpha-particle scattering experiment conducted by Geiger and Marsden?

Correct Answer: B

Q5.Which model of the atom suggests that the positive charge is uniformly distributed throughout the atom, with electrons embedded like seeds in a watermelon?

Correct Answer: A

Q6.In the context of atomic spectra, which series of spectral lines is associated with the ultraviolet region?

Correct Answer: C

Q7.In the context of atomic spectra, which series of spectral lines is associated with the infrared region?

Correct Answer: C

Q8.What is the primary reason Rutherford's model could not explain the atomic spectra?

Correct Answer: B

Q9.What was the primary conclusion of Rutherford's gold foil experiment?

Correct Answer: C

Q10.Which of the following best describes the arrangement of electrons in J. J. Thomson's model of the atom?

Correct Answer: A

Q11.Which spectral series of hydrogen is visible in the visible spectrum?

Correct Answer: B

Q12.Ernst Rutherford's experiments led to the discovery of which fundamental component of the atom?

Correct Answer: C

Q13.Which of the following statements about the emission spectrum of hydrogen is correct?

Correct Answer: C

Q14.What characteristic of light emitted by rarefied gases distinguishes it from that of dense gases?

Correct Answer: B

Q15.Which model of the atom describes it as having electrons embedded in a positively charged sphere, similar to seeds in a watermelon?

Correct Answer: A

Q16.Who performed the classic experiment on the scattering of alpha particles to investigate atomic structure?

Correct Answer: C

Q17.Which of the following series corresponds to the visible spectrum in the hydrogen emission spectrum?

Correct Answer: B

Q18.Which of the following series is part of the hydrogen emission spectrum and is visible in the visible spectrum?

Correct Answer: B

Q19.What is the main characteristic of the light emitted from rarefied gases when excited electrically?

Correct Answer: B

Q20.In the context of atomic spectra, which of the following statements best explains why rarefied gases emit light at discrete wavelengths?

Correct Answer: A

Q21.Who was the physicist that proposed the experiment leading to the discovery of the atomic nucleus?

Correct Answer: C

Q22.Which of the following series of the hydrogen emission spectrum is visible in the infrared region?

Correct Answer: C

Q23.Which physicist is known for discovering alpha-rays and beta-rays?

Correct Answer: B

Q24.Which experiment led to the discovery of the atomic nucleus?

Correct Answer: B

Q25.What did J. J. Thomson's experiments on electric discharge through gases reveal about atoms?

Correct Answer: B

Q26.What was the primary finding from the experiments conducted by Geiger and Marsden under Rutherford's guidance?

Correct Answer: B

Q27.Which of the following best explains why the Balmer series is visible in the visible spectrum?

Correct Answer: A

Q28.Which scientist's experiments revealed that atoms contain negatively charged constituents known as electrons?

Correct Answer: A

Q29.Which of the following statements about the Balmer series is correct?