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Democritus (~460 BCE - ~370 BCE) Stephanie

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Democritus (~460 BCE - ~370 BCE) Stephanie

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Name of Model: N/A

There was no model made, Democritus just introduced the concept for the atom "atomos". His idea was unable to be conceptualized.

Image of Model: N/A

Experiment Conclusions:

Democritus came up with the concept that all matter is made up of small particles called atoms "atomos" which means indivisible, apart from this, atoms can not be created of destroyed. He did not use any material because he just came up with the idea and didn't follow through with an experiment.

Pros:

Democritus began the idea of the atom which makes up all matter, this would later become the foundation for scientists studying the atom in the future. Democritus also stated that atoms are indivisible and cannot be created or destroyed which helped Dalton with his atomic theory.

Cons:

Democritus was not able to make a model of his idea and he was very vague with his explanation due to lack of research and support by other philosophers.

Conclusion: About 400 B.C. the Greek philosopher Democritus suggested that all matter was formed of different types of tiny discrete particles and that the properties of these particles also determined the properties of matter.

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Dalton's Solid Sphere Model / Discovered in 1803

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Name of Model:

Dalton's Solid Sphere Model

Experiment Conclusions

According to the Solid Sphere Model:
Dalton's Solid Sphere Model represents one of the earliest attempts to understand the fundamental nature of matter at the atomic level. Nevertheless, it is essential to emphasize that this model has been surpassed by more modern atomic models, including the Bohr model and the Quantum Mechanical Model. Dalton used oxygen for his experiment and other gases.

Pros :

One of the main pros of this model being that it was simple and not complex. Dalton's model was simple and easy to understand. It proposed that atoms were tiny, indivisible,and solid spheres with no internal structure.

Cons:

One of the main cons about this model it's that it's outdated. As the model is fundamentally flawed as it suggests that atoms are indivisible and solid spheres, which we now know to be incorrect. Atoms are composed of subatomic particles (protons, neutrons, and electrons) and have a complex internal structure.

Conclusion: John Dalton (1766-1844) was an English chemist, physicist, and meteorologist, best known for introducing the atomic theory into chemistry and for his work on human optics.

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Name of Model:Plum Pudding Model

Experiment Conclusions:Plum Pudding Model conclude in the that (atoms, electrons, and protons) don't have define place they are just there lake a mass for example a cookie because is not a define shape and chocolate chps don't have a define place. For conclude from the cathode ray tube experiment that the atom can be divided into smaller particles.

Pros:the 3 best way to explain the pros of J.J. Thomson model are the next ones.

-It successfully explained electron neutrality of an atom

-It was the first atomic model which was simple and visual

-Was easy to explain's in vase of the water melon

Cons: In the other hand J.J. Thomson until was maybe easy to explain was missing some factors...

-Most of the space in an atom is empty

-One of the major drawbacks of his model is that there were no experimental pieces of evidence provided by him

-In this model there was no mention of the nucleus of an atom

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Name of Model:

Nuclear model / Rutherford's model

Experiment Conclusions:

According to the Rutherford atomic model using gold foil and alpha particles: The positive charge and most of the mass of an atom is concentrated in an extremely small volume. He called this region of the atom as a nucleus. Rutherford's model proposed that the negatively charged electrons surround the nucleus of an atom.

Pros:

He imagined electrons revolving around the nucleus like planets around the sun. He assumed most of the atoms were hollow.

Cons:

This atomic model failed to explain the stability of atoms, According to the model, electrons revolve around the positively charged nucleus, and this model of the atom also failed to explain the existence of definite lines in the hydrogen spectrum.

SITES: https://byjus.com/chemistry/rutherfords-model-of-atoms-and-its-limitations/#:~:text=According%20to%20the%20Rutherford%20atomic,the%20nucleus%20of%20an%20atom.

https://unacademy.com/content/neet-ug/study-material/physics/rutherford-atomic-model/#:~:text=Advantages%20of%20Rutherford%20model&text=He%20imagined%20electrons%20revolving%20around,known%20to%20be%20electrically%20neutral.

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Name of Model:

Planetary Model

Experiment Conclusions:

He used atomic emission spectrum of Hydrogen. He concluded that the electrons will have more energy if it is located further away from the nucleus but when the the electrons are closer to the nucleus they will have less energy.

Bohr model of an atom: This model represents that the electrons travel around the nucleus of an atom in distinct circular orbits, or shells.

Pros:

One of the main advantages of Bohr model is that it had the ability to explain the atomic emission spectra observed in experiments. It also allowed the calculation of energy levels for electrons in hydrogen and hydrogen-like atoms. As well, it introduced the concept of stable electron orbits.

Cons:

One of the main disadvantages of Bohr model is that it struggled to explain the behavior of multi-electron due to the complexities arising from electron-electron interactions and the presence of more intricate energy levels.

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 Schrödinger Quantum Mechanical Model / Discovered in 1926

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Erwin Schrodinger (1887 - 1961) Alexandra

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Erwin Schrodinger (1887 - 1961) Alexandra

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Name of Model

Schrödinger Quantum Mechanical Model

Experiment Conclusions:

The Schrödinger Quantum Mechanical Model, often referred to as the Schrödinger Wave Equation, serves as a foundational theory of quantum mechanics. It provides a comprehensive description of the behavior of particles at both the atomic and subatomic scales.

Pros:One of the pros to Schrödinger's model being that it provides a highly accurate predictions of the behavior of electrons in atoms and molecules.

Cons: One of the main cons of this model being that in many cases, exact solutions to the Schrödinger equation are not feasible, and approximations must be made. These approximations may introduce errors in predictions.

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Name of Model:

Chadwick's Quantum Mechanical Model / Chadwick's Atomic Model

Experiment Conclusions:

James Chadwick used Beryllium and bombarded it with alpha particles. He discovered that there was actually a neutral particle in the nucleus, the neutron. He also concluded that the mass of the neutron was very similar to the one of a proton only differing by 0.1 percent.

Pros :

He discovered that the nucleus contained another subatomic particle that held no charge, the neutron. He changed the way the nucleus was modeled and it helped create one of the most accurate atomic models.

Cons:

Chadwick's model lacked specific information about electrons like the electron cloud since he focused more on the nucleus. In his model he also made the atomic structure and behavior look less complex making it slightly inaccurate.

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Erwin Schrödinger

https://www.collimator.ai/reference-guides/what-is-the-schrodinger-equation

Pros: https://study.com/learn/lesson/the-quantum-mechanical-model-definition-overview.html

Cons: https://www.sciencedirect.com/topics/physics-and-astronomy/schroedinger-equation

Democritus

https://www.ucl.ac.uk/~ucfbasc/Basic/Atheory.html#:~:text=About%20400%20B.C.%20the%20Greek,determined%20the%20properties%20of%20matter.

https://www.famousscientists.org/democritus/

J.J. Thomson

https://www.khanacademy.org/science/chemistry/electronic-structure-of-atoms/history-of-atomic-structure/a/discovery-of-the-electron-and-nucleus#:~:text=Summary-,J.J.,positively%2Dcharged%20%22soup.%22

Ernest Rutherford

https://www.khanacademy.org/science/chemistry/electronic-structure-of-atoms/history-of-atomic-structure/v/rutherfords-gold-foil-experiment

Niels Bohr

https://www.britannica.com/science/Bohr-model

James Chadwick

https://www.famousscientists.org/james-chadwick/

In general

https://www.famousscientists.org

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The postulates of Dalton's atomic theory: which points do we still use today, and what have we learned since Dalton?

Dalton's atomic theory was the first complete attempt to describe all matter in terms of atoms and their properties.

Dalton based his theory on the law of conservation of mass and the law of constant composition.

The first part of his theory states that all matter is made of atoms, which are indivisible.

The second part of the theory says all atoms of a given element are identical in mass and properties.

The third part says compounds are combinations of two or more different types of atoms.

The fourth part of the theory states that a chemical reaction is a rearrangement of atoms.

Parts of the theory had to be modified based on the discovery of subatomic particles and isotopes.

Chemists ask questions.

Chemistry is full of unanswered questions. One of the first questions people have been asking since ancient times is What is the world made of?

That is, if we were to zoom in ~100000000000 times-that is 11 zeros!-on the skin of your fingertip, what would we see? Would that look any different from zooming in on, say, an apple? If we then cut up the apple into tinier and tinier pieces using an imaginary tiny knife, would we reach a point where the pieces could no longer be cut any smaller? What would those pieces look like, and would they still have apple properties?

The answers to these questions are fundamental to modern chemistry, and chemists didn't agree on the answer until a few hundred years ago. Thanks to scientists such as John Dalton, modern chemists think of the world in terms of atoms. Even if we can't see atoms with our naked eye, properties of matter such as color, phase (e.g., solid, liquid, gas), and even smell come from interactions on an atomic level. This article will discuss John Dalton's atomic theory, which was the first complete attempt to describe all matter in terms of atoms and their properties.

Basis for Dalton's theory

Dalton based his theory on two laws: the law of conservation of mass and the law of constant composition.

The law of conservation of mass says that matter is not created or destroyed in a closed system. That means if we have a chemical reaction, the amount of each element must be the same in the starting materials and the products. We use the law of conservation of mass every time we balance equations!

The law of constant composition says that a pure compound will always have the same proportion of the same elements. For example, table salt, which has the molecular formula , contains the same proportions of the elements sodium and chlorine no matter how much salt you have or where the salt came from. If we were to combine some sodium metal and chlorine gas-which I wouldn't recommend doing at home-we could make more table salt which will have the same composition.

Concept check: A time-travelling scientist from the early 1700s decides to run the following experiment: he takes a 10 gram sample of ethanol () and burns it in the presence of oxygen in an open beaker. After the reaction is done, the beaker is empty. Does this result violate the law of conservation of mass?

Dalton's atomic theory

Part 1: All matter is made of atoms.

Dalton hypothesized that the law of conservation of mass and the law of definite proportions could be explained using the idea of atoms. He proposed that all matter is made of tiny indivisible particles called atoms, which he imagined as "solid, massy, hard, impenetrable, movable particle(s)".

It is important to note that since Dalton did not have the necessary instruments to see or otherwise experiment on individual atoms, he did not have any insight into whether they might have any internal structure. We might visualize Dalton's atom as a piece in a molecular modeling kit, where different elements are spheres of different sizes and colors. While this is a handy model for some applications, we now know that atoms are far from being solid spheres.

Part 2: All atoms of a given element are identical in mass and properties.

Dalton proposed that every single atom of an element, such as gold, is the same as every other atom of that element. He also noted that the atoms of one element differ from the atoms of all other elements. Today, we still know this to be mostly true. A sodium atom is different from a carbon atom. Elements may share some similar boiling points, melting points, and electronegativities, but no two elements have the same exact set of properties.

Part 3: Compounds are combinations of two or more different types of atoms.

In the third part of Dalton's atomic theory, he proposed that compounds are combinations of two or more different types of atoms. An example of such a compound is table salt. Table salt is a combination of two separate elements with unique physical and chemical properties. The first, sodium, is a highly reactive metal. The second, chlorine, is a toxic gas. When they react, the atoms combine in a 1:1 ratio to form white crystals of , which we can sprinkle on our food.

Since atoms are indivisible, they will always combine in simple whole number ratios. Therefore, it would not make sense to write a formula such as because you can't have half of an atom!

Part 4: A chemical reaction is a rearrangement of atoms.

In the fourth and final part of Dalton's atomic theory, he suggested that chemical reactions don't destroy or create atoms. They merely rearranged the atoms. Using our salt example again, when sodium combines with chlorine to make salt, both the sodium and chlorine atoms still exist. They simply rearrange to form a new compound.

What have we learned since Dalton proposed his theory?

The short answer: a lot! For instance, we now know that atoms are not indivisible-as stated in part one-because they are made up of protons, neutrons, and electrons. The modern picture of an atom is very different from Dalton's "solid, massy" particle. In fact, experiments by Ernest Rutherford, Hans Geiger, and Ernest Marsden showed that atoms are mostly made up of empty space.

Part two of Dalton's theory had to be modified after mass spectrometry experiments demonstrated that atoms of the same element can have different masses because the number of neutrons can vary for different isotopes of the same element. For more on isotopes, you can watch this video on atomic number, mass number, and isotopes.

Despite these caveats, Dalton's atomic theory is still mostly true, and it forms the framework of modern chemistry. Scientists have even developed the technology to see the world on an atomic level!

Dalton's atomic theory was the first complete attempt to describe all matter in terms of atoms and their properties.

Dalton based his theory on the law of conservation of mass and the law of constant composition.

The first part of his theory states that all matter is made of atoms, which are indivisible.

The second part of the theory says all atoms of a given element are identical in mass and properties.

The third part says compounds are combinations of two or more different types of atoms.

The fourth part of the theory states that a chemical reaction is a rearrangement of atoms.

Parts of the theory had to be modified based on the existence of subatomic particles and isotopes.

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Dalton's atomic theory (article) | Khan Academy

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