TUNMISE ANIYI
MODELS OF
ATOMIC STRUCTURE
Index
Lithium
1.
Introduction/Purpose
2.
Timeline Overview
3.
Dalton model information
4.
Dalton- Experiments conducted & limitations
5.
Thomson model information
6.
Thomson- Exeriments conducted & limitations
7.
Rutherford model information
8.
Rutherford- Experiments conducted & limitations
9.
Bohr model information
10.
Bohr- Experiments conducted & limitations
atom
11.
Summary
12.
References
Introduction/ Purpose
The purpose of this presentation is to briefly summarise the atomic models of Dalton, Thomson, Rutherford and Bohr. Each model is explained with information on the model itself, the experiments conducted/ evidence gathered that supports the model, and relevant limitations on the model.
Models from 1803-1913
Timeline
Timeline of four of the Atomic Models
Dalton Atomic Model Information
The first complete attempt to describe all matter in terms of atoms and their properties.
The Billiard Model- 1803
Solid sphere model based on the laws of conservation of mass, constant proportions, multiple proportions, and reciprocal proportions.
Dalton thought atoms were the smallest particles of matter that could not be divided any further, he envisioned them as solid, hard spheres, like billiard (pool) balls, so he used wooden balls to model them. Holes were purposefully added to the balls so that they could be added together with hooks to form compounds.
Dalton's experiments and model limitations
Limitations
Experiments and Research conducted
Some limitations are that Dalton’s atomic model does not account for subatomic particles. Dalton’s atomic theory originally stated that atoms were indivisible, however the discovery of subatomic particles (protons, electrons, and neutrons) disproved this hypothesis.
Dalton investigated pressure and other properties of gases, from which he inferred that gases must consist of tiny, individual particles that are in constant, random notion.
Dalton researched the properties of compounds, what are substances that consist of more than one element. He showed that a given compound is always comprised of the same elements in the same whole-number ratio and that different compounds consist of different elements or ratios. Dalton decided that this could only happen if elements are made of separate, discrete particles that cannot be subdivided.
Figure shows Dalton's symbols depicting each element and atomic/ molecular structure
Thomson Atomic Model Information
Plum Pudding Model- 1897
J.J Thomson discovered the first subatomic particle, the electron, while researching cathode rays. Thomson proposed a model of an atom in which negative electrons are scattered throughout a sphere of positive charge to explain the neutrality of atoms.
Thomson's experiment and model limitations
Cathode ray experiment
Thomson passed current through a cathode ray tube, a glass tube from which virtually all of the air has been removed. Metal is placed on both ends, on positively charged the other negative, allowing a cathode ray to travel end to end when a high voltage electric current is applied.
To test whether a cathode ray was a stream of moving particles, Thomson placed negative and positive plates along the sides of the cathode ray to see the reaction. The ray appeared to be repelled by the negative plate and attracted to the positive plate, meaning the ray was negatively charged and must therefore, contain particles that have mass. The particles were originally named “corpuscles”, but they were later renamed electrons.
Through this find, Thomson has discovered particles smaller than atoms, disproving Dalton’s theory.
Limitations
Thomson’s atomic model failed to explain how the positive charge holds the electrons inside the atom. It also failed to the stability of an atom. Thomson’s theory did not mention anything about the nucleus of an atom.
Figure shows Thomson's cathode ray experiment
Rutherford Atomic Model Information
Nuclear Model- 1911
Rutherford’s model described the atom as a tiny, dense, positively charged core called a nucleus, in which all the mass is concentrated, around which the light, negatively constituents, called electrons, circulate at some distance, much like planets revolving around the sun.
Rutherford's experiment and model limitations
Rutherfurd’s gold foil experiment showed that the atom is mostly empty space with a tiny, dense, positively charged nucleus. Rutherford shot a thin beam of alpha particles (helium nuclei) at a very thin sheet of pure gold. A sample of radium (a radioactive metal) was placed in a lead box with a pinhole in it. Most of the radiation was absorbed by the lead, but a thin beam of alpha particles escaped out the pinhole in the direction of the gold foil. The gold foil was surrounded by a detector screen that would flash when hit with an alpha particle. Due to Thomson’s previous prediction of the positive charge being spread out through the entire volume of the atom, Rutherford predicted the alpha particles would pass through the gold foil. This was due to the positively charge fill being too weak to significantly affect the path of the relatively big and fast-moving alpha particles. However, while most particles passed through the gold foil, a few alpha particles were deflected more than 90degrees from their path.
Figure shows Rutherford's gold foil experiment
Limitations
Rutherford’s model failed to explain the stability of atoms.
The arrangement of electrons in a circular path was not defined. Particles moving in a circular path undergo acceleration and radiates energy. Therefore, the revolving electron would lose energy and eventually fall into the nucleus.
Figure shows Rutherford's experiment result next to Thomson's model
Planetary Model- 1913
Bohr's model
Bohr Atomic Model Information
The Bohr model shows a small positively charged atom, surrounded by revolving negatively charged electrons in fixed orbits. Bohr was the first to discover electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element.
Electrons will have more energy if it is located away from the nucleus, whereas the electrons will have less energy if it is located near the nucleus.
Bohr's experiment and model limitations
The Bohr model considers electrons to have both a known radius and orbit, which is impossible according to Heisenberg.
It cannot predict the relative intensities of spectral lines.
Limitations
Figure shows Bohr's hydrogen experiment
Experiment and Research
Bohr developed his model after studying the way glowing, hot hydrogen gives off light.
When an incandescent lightbulb is lit it gives off all the different wavelengths of light as the filament heats up. However, when hydrogen gas is heated to a high temperature a discrete wavelength- a line in the red of just one wavelength, is seen. A line may also be seen I the blue, yellow and possibly other lines. Each line has a specific wavelength.
Bohr suggested that this implies that electrons have to adopt very specific energy levels in an atom, rather than being at any possible level. The glowing hydrogen lines represent times when electrons jump from a higher energy level to a lower energy level, emitting a photon of visible light at those specific wavelengths. According to the first law of conservation, energy has to be conserved. Therefore, the energy lost from jumping is emitted as a photon.
Summary
As a result of the discovery of subatomic particles. the Dalton model has changed. Each discovery builiding and challenging the intial thought prior. Bohr improved Rutherford’s model. Using mathematical ideas, he showed that electrons occupy shells or energy levels around the nucleus. Rutherford unintentionally disproved Thomson's earlier hypothesis while performing his gold foil experiment. Finally, Thomson refuted Dalton's model with his discovery of the first subatomic particle, the electron, with researching cathode rays
Khan Academy. (2023a). Retrieved February 16, 2023, from Khanacademy.org website: https://www.khanacademy.org/science/chemistry/electronic-structure-of-atoms/history-of-atomic-structure/a/discovery-of-the-electron-and-nucleus#:~:text=Rutherford's%20gold%20foil%20experiment%20showed,nuclear%20model%20of%20the%20atom.
Khan Academy. (2023b). Retrieved February 19, 2023, from Khanacademy.org website: https://www.khanacademy.org/science/ap-chemistry-beta/x2eef969c74e0d802:atomic-structure-and-properties/x2eef969c74e0d802:mass-spectrometry-of-elements/v/mass-spectrometry#:~:text=In%20the%20analytical%20technique%20of,ratios%20(m%2Fz).
More. (2019, January 10). What Are The Different Atomic Models? Dalton, Rutherford, Bohr and Heisenberg Models Explained. Retrieved February 16, 2023, from Science ABC website: https://www.scienceabc.com/pure-sciences/dalton-atomic-model.html
Peterson, E. (2017, August 29). Niels Bohr: Biography & Atomic Theory. Retrieved February 16, 2023, from livescience.com website: https://www.livescience.com/32016-niels-bohr-atomic-theory.html#:~:text=Atomic%20model,-Bohr's%20greatest%20contribution&text=The%20Bohr%20model%20shows%20the,the%20properties%20of%20an%20element.
Rutherford model | Definition & Facts | Britannica. (2023). In Encyclopædia Britannica. Retrieved from https://www.britannica.com/science/Rutherford-model
sathyabama.sathyamurthi@qbslearning.com. (2021, August). Niels Bohr and the Bohr Atom Model. Retrieved February 16, 2023, from Wondrium Daily website: https://www.wondriumdaily.com/niels-bohr-and-the-bohr-atom-model/#:~:text=It%20was%20while%20Bohr%20was,the%20different%20wavelengths%20of%20light.
Admin. (2015, December 19). John Dalton’s Atomic Theory - Postulates & Limitations with FAQs and Examples. Retrieved February 16, 2023, from BYJUS website: https://byjus.com/chemistry/daltons-atomic-theory/#:~:text=in%20chemical%20reactions.-,Limitations%20of%20Dalton's%20Atomic%20Theory,and%20neutrons)%20disproved%20this%20postulate.
Bohr’s Hydrogen Atom. (2013, October 2). Retrieved February 16, 2023, from Chemistry LibreTexts website: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Quantum_Mechanics/09._The_Hydrogen_Atom/Bohr's_Hydrogen_Atom#:~:text=The%20Bohr%20Model%20is%20very,presence%20of%20a%20magnetic%20field.
BYJU'S. (2022, July 4). What are the limitations of Rutherford-s model of the atom- - ChemistryQuestion. Retrieved February 16, 2023, from Byjus.com website: https://byjus.com/question-answer/what-are-the-limitations-of-rutherfords-model-of-the-atom/
CK-12 Foundation. (2023a). CK12-Foundation. Retrieved February 16, 2023, from CK-12 Foundation website: https://flexbooks.ck12.org/cbook/ck-12-middle-school-physical-science-flexbook-2.0/section/3.12/primary/lesson/daltons-atomic-theory-ms-ps/
CK-12 Foundation. (2023b). CK12-Foundation. Retrieved February 16, 2023, from CK-12 Foundation website: https://flexbooks.ck12.org/cbook/ck-12-middle-school-physical-science-flexbook-2.0/section/3.13/primary/lesson/thomsons-atomic-model-ms-ps/
References
Bibliography
Toppr. (2020, January 9). Describe Bohr’s model of the atom. Retrieved February 16, 2023, from Toppr Ask website: https://www.toppr.com/ask/question/describe-bohrs-model-of-the-atom/
Toppr-guides. (2018, February 16). Retrieved February 16, 2023, from Toppr-guides website: https://www.toppr.com/guides/chemistry/structure-of-atom/thomsons-model-of-an-atom/#:~:text=Source%20Credit%3A%20Wikipedia)-,Limitations%20of%20Thomson's%20Atomic%20Model,the%20nucleus%20of%20an%20atom.
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Transcript
TUNMISE ANIYI
MODELS OF
ATOMIC STRUCTURE
Index
Lithium
1.
Introduction/Purpose
2.
Timeline Overview
3.
Dalton model information
4.
Dalton- Experiments conducted & limitations
5.
Thomson model information
6.
Thomson- Exeriments conducted & limitations
7.
Rutherford model information
8.
Rutherford- Experiments conducted & limitations
9.
Bohr model information
10.
Bohr- Experiments conducted & limitations
atom
11.
Summary
12.
References
Introduction/ Purpose
The purpose of this presentation is to briefly summarise the atomic models of Dalton, Thomson, Rutherford and Bohr. Each model is explained with information on the model itself, the experiments conducted/ evidence gathered that supports the model, and relevant limitations on the model.
Models from 1803-1913
Timeline
Timeline of four of the Atomic Models
Dalton Atomic Model Information
The first complete attempt to describe all matter in terms of atoms and their properties.
The Billiard Model- 1803
Solid sphere model based on the laws of conservation of mass, constant proportions, multiple proportions, and reciprocal proportions.
Dalton thought atoms were the smallest particles of matter that could not be divided any further, he envisioned them as solid, hard spheres, like billiard (pool) balls, so he used wooden balls to model them. Holes were purposefully added to the balls so that they could be added together with hooks to form compounds.
Dalton's experiments and model limitations
Limitations
Experiments and Research conducted
Some limitations are that Dalton’s atomic model does not account for subatomic particles. Dalton’s atomic theory originally stated that atoms were indivisible, however the discovery of subatomic particles (protons, electrons, and neutrons) disproved this hypothesis.
Dalton investigated pressure and other properties of gases, from which he inferred that gases must consist of tiny, individual particles that are in constant, random notion. Dalton researched the properties of compounds, what are substances that consist of more than one element. He showed that a given compound is always comprised of the same elements in the same whole-number ratio and that different compounds consist of different elements or ratios. Dalton decided that this could only happen if elements are made of separate, discrete particles that cannot be subdivided.
Figure shows Dalton's symbols depicting each element and atomic/ molecular structure
Thomson Atomic Model Information
Plum Pudding Model- 1897
J.J Thomson discovered the first subatomic particle, the electron, while researching cathode rays. Thomson proposed a model of an atom in which negative electrons are scattered throughout a sphere of positive charge to explain the neutrality of atoms.
Thomson's experiment and model limitations
Cathode ray experiment
Thomson passed current through a cathode ray tube, a glass tube from which virtually all of the air has been removed. Metal is placed on both ends, on positively charged the other negative, allowing a cathode ray to travel end to end when a high voltage electric current is applied. To test whether a cathode ray was a stream of moving particles, Thomson placed negative and positive plates along the sides of the cathode ray to see the reaction. The ray appeared to be repelled by the negative plate and attracted to the positive plate, meaning the ray was negatively charged and must therefore, contain particles that have mass. The particles were originally named “corpuscles”, but they were later renamed electrons. Through this find, Thomson has discovered particles smaller than atoms, disproving Dalton’s theory.
Limitations
Thomson’s atomic model failed to explain how the positive charge holds the electrons inside the atom. It also failed to the stability of an atom. Thomson’s theory did not mention anything about the nucleus of an atom.
Figure shows Thomson's cathode ray experiment
Rutherford Atomic Model Information
Nuclear Model- 1911
Rutherford’s model described the atom as a tiny, dense, positively charged core called a nucleus, in which all the mass is concentrated, around which the light, negatively constituents, called electrons, circulate at some distance, much like planets revolving around the sun.
Rutherford's experiment and model limitations
Rutherfurd’s gold foil experiment showed that the atom is mostly empty space with a tiny, dense, positively charged nucleus. Rutherford shot a thin beam of alpha particles (helium nuclei) at a very thin sheet of pure gold. A sample of radium (a radioactive metal) was placed in a lead box with a pinhole in it. Most of the radiation was absorbed by the lead, but a thin beam of alpha particles escaped out the pinhole in the direction of the gold foil. The gold foil was surrounded by a detector screen that would flash when hit with an alpha particle. Due to Thomson’s previous prediction of the positive charge being spread out through the entire volume of the atom, Rutherford predicted the alpha particles would pass through the gold foil. This was due to the positively charge fill being too weak to significantly affect the path of the relatively big and fast-moving alpha particles. However, while most particles passed through the gold foil, a few alpha particles were deflected more than 90degrees from their path.
Figure shows Rutherford's gold foil experiment
Limitations
Rutherford’s model failed to explain the stability of atoms. The arrangement of electrons in a circular path was not defined. Particles moving in a circular path undergo acceleration and radiates energy. Therefore, the revolving electron would lose energy and eventually fall into the nucleus.
Figure shows Rutherford's experiment result next to Thomson's model
Planetary Model- 1913
Bohr's model
Bohr Atomic Model Information
The Bohr model shows a small positively charged atom, surrounded by revolving negatively charged electrons in fixed orbits. Bohr was the first to discover electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element. Electrons will have more energy if it is located away from the nucleus, whereas the electrons will have less energy if it is located near the nucleus.
Bohr's experiment and model limitations
The Bohr model considers electrons to have both a known radius and orbit, which is impossible according to Heisenberg. It cannot predict the relative intensities of spectral lines.
Limitations
Figure shows Bohr's hydrogen experiment
Experiment and Research
Bohr developed his model after studying the way glowing, hot hydrogen gives off light. When an incandescent lightbulb is lit it gives off all the different wavelengths of light as the filament heats up. However, when hydrogen gas is heated to a high temperature a discrete wavelength- a line in the red of just one wavelength, is seen. A line may also be seen I the blue, yellow and possibly other lines. Each line has a specific wavelength. Bohr suggested that this implies that electrons have to adopt very specific energy levels in an atom, rather than being at any possible level. The glowing hydrogen lines represent times when electrons jump from a higher energy level to a lower energy level, emitting a photon of visible light at those specific wavelengths. According to the first law of conservation, energy has to be conserved. Therefore, the energy lost from jumping is emitted as a photon.
Summary
As a result of the discovery of subatomic particles. the Dalton model has changed. Each discovery builiding and challenging the intial thought prior. Bohr improved Rutherford’s model. Using mathematical ideas, he showed that electrons occupy shells or energy levels around the nucleus. Rutherford unintentionally disproved Thomson's earlier hypothesis while performing his gold foil experiment. Finally, Thomson refuted Dalton's model with his discovery of the first subatomic particle, the electron, with researching cathode rays
Khan Academy. (2023a). Retrieved February 16, 2023, from Khanacademy.org website: https://www.khanacademy.org/science/chemistry/electronic-structure-of-atoms/history-of-atomic-structure/a/discovery-of-the-electron-and-nucleus#:~:text=Rutherford's%20gold%20foil%20experiment%20showed,nuclear%20model%20of%20the%20atom. Khan Academy. (2023b). Retrieved February 19, 2023, from Khanacademy.org website: https://www.khanacademy.org/science/ap-chemistry-beta/x2eef969c74e0d802:atomic-structure-and-properties/x2eef969c74e0d802:mass-spectrometry-of-elements/v/mass-spectrometry#:~:text=In%20the%20analytical%20technique%20of,ratios%20(m%2Fz). More. (2019, January 10). What Are The Different Atomic Models? Dalton, Rutherford, Bohr and Heisenberg Models Explained. Retrieved February 16, 2023, from Science ABC website: https://www.scienceabc.com/pure-sciences/dalton-atomic-model.html Peterson, E. (2017, August 29). Niels Bohr: Biography & Atomic Theory. Retrieved February 16, 2023, from livescience.com website: https://www.livescience.com/32016-niels-bohr-atomic-theory.html#:~:text=Atomic%20model,-Bohr's%20greatest%20contribution&text=The%20Bohr%20model%20shows%20the,the%20properties%20of%20an%20element. Rutherford model | Definition & Facts | Britannica. (2023). In Encyclopædia Britannica. Retrieved from https://www.britannica.com/science/Rutherford-model sathyabama.sathyamurthi@qbslearning.com. (2021, August). Niels Bohr and the Bohr Atom Model. Retrieved February 16, 2023, from Wondrium Daily website: https://www.wondriumdaily.com/niels-bohr-and-the-bohr-atom-model/#:~:text=It%20was%20while%20Bohr%20was,the%20different%20wavelengths%20of%20light.
Admin. (2015, December 19). John Dalton’s Atomic Theory - Postulates & Limitations with FAQs and Examples. Retrieved February 16, 2023, from BYJUS website: https://byjus.com/chemistry/daltons-atomic-theory/#:~:text=in%20chemical%20reactions.-,Limitations%20of%20Dalton's%20Atomic%20Theory,and%20neutrons)%20disproved%20this%20postulate. Bohr’s Hydrogen Atom. (2013, October 2). Retrieved February 16, 2023, from Chemistry LibreTexts website: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Quantum_Mechanics/09._The_Hydrogen_Atom/Bohr's_Hydrogen_Atom#:~:text=The%20Bohr%20Model%20is%20very,presence%20of%20a%20magnetic%20field. BYJU'S. (2022, July 4). What are the limitations of Rutherford-s model of the atom- - ChemistryQuestion. Retrieved February 16, 2023, from Byjus.com website: https://byjus.com/question-answer/what-are-the-limitations-of-rutherfords-model-of-the-atom/ CK-12 Foundation. (2023a). CK12-Foundation. Retrieved February 16, 2023, from CK-12 Foundation website: https://flexbooks.ck12.org/cbook/ck-12-middle-school-physical-science-flexbook-2.0/section/3.12/primary/lesson/daltons-atomic-theory-ms-ps/ CK-12 Foundation. (2023b). CK12-Foundation. Retrieved February 16, 2023, from CK-12 Foundation website: https://flexbooks.ck12.org/cbook/ck-12-middle-school-physical-science-flexbook-2.0/section/3.13/primary/lesson/thomsons-atomic-model-ms-ps/
References
Bibliography
Toppr. (2020, January 9). Describe Bohr’s model of the atom. Retrieved February 16, 2023, from Toppr Ask website: https://www.toppr.com/ask/question/describe-bohrs-model-of-the-atom/ Toppr-guides. (2018, February 16). Retrieved February 16, 2023, from Toppr-guides website: https://www.toppr.com/guides/chemistry/structure-of-atom/thomsons-model-of-an-atom/#:~:text=Source%20Credit%3A%20Wikipedia)-,Limitations%20of%20Thomson's%20Atomic%20Model,the%20nucleus%20of%20an%20atom.