What Are The Different Atomic Models? Dalton, Rutherford, Bohr and Heisenberg Models Explained

Summary

This script takes viewers on a historical journey through the evolution of atomic theory, from Democritus' concept of atomos to Dalton's atomic model and beyond. It highlights key scientific milestones, such as the 'plum pudding' model by J.J. Thompson, Rutherford's discovery of the atomic nucleus, and Bohr's quantum theory. The narrative culminates with Schrödinger's quantum mechanical model, illustrating the profound transformation in our understanding of atomic structure and the relentless pursuit of knowledge.

Takeaways

• 🏀 The concept of 'basketball' often brings to mind an orange sphere or a favorite athlete's dunk.
• 🌐 Ancient Greek philosopher Democritus theorized that everything was made of 'atomos', meaning 'uncuttable', and that the properties of materials depended on the type of atomos they were composed of.
• 🔍 Aristotle's theory of four elements (earth, fire, water, air) largely discredited Democritus' theory.
• 🧪 British chemist John Dalton proposed the law of multiple proportions and the theory of atomism, suggesting that everything is made up of unique atoms.
• 🔬 Dalton's atomic model described atoms as tiny, indestructible solid spheres, with different elements' atoms combining to form compounds.
• 🍮 J.J. Thompson's 'plum pudding' model depicted atoms as positively charged masses with tiny negative charges embedded, like plums in pudding.
• 🔳 Ernest Rutherford's gold-foil experiment led to a new atomic model, proposing a concentrated positively charged center (nucleus) with electrons orbiting around it.
• 🌐 Niels Bohr introduced the concept of quantized energy, suggesting electrons move in fixed orbits or shells around the nucleus.
• 🌌 Quantum mechanics, particularly the Heisenberg Uncertainty principle, challenged Bohr's model by stating it's impossible to know the exact position and trajectory of electrons.
• 🔬 Erwin Schrödinger's quantum mechanical model described electrons not in fixed orbits but as electron clouds in atomic orbitals, where the probability of finding an electron is highest.

Q & A

What was the first concept of atoms proposed by Democritus?

Democritus proposed that everything in the world was made of tiny indestructible particles called 'atomos', which means 'uncuttable', and that the properties of materials depended on the type of atomos they were composed of.

How did Aristotle's view of the composition of the world differ from Democritus's theory?

Aristotle believed that everything on the planet was made of four elements: earth, fire, water, and air, which was in contrast to Democritus's idea of 'atomos'.

What experiment led John Dalton to propose the law of multiple proportions and the theory of atomism?

John Dalton conducted experiments where he mixed two gases and observed their behavior, particularly noting the fixed ratio in which gases reacted with each other.

What was the 'plum pudding' model of the atom proposed by J.J. Thompson?

The 'plum pudding' model characterized an atom as a particle composed of a positively charged mass with tiny negative charges embedded in it, similar to plums in a pudding.

What experiment did Ernest Rutherford conduct to probe the structure of an atom?

Rutherford conducted the gold-foil experiment, also known as the Geiger–Marsden experiment, which involved a thin sheet of gold foil and a screen coated with Zinc Sulphide to detect alpha particles.

What did Rutherford's observations of the gold-foil experiment lead to in terms of atomic structure?

Rutherford proposed an atomic structure where most of the atom's mass was concentrated in a positively charged center, later named the nucleus, with electrons orbiting around it.

What discrepancy did Niels Bohr find in Rutherford's atomic model?

Bohr found that if electrons were orbiting around a positively charged center, they would lose their energy and collapse into the nucleus, which contradicted the observed stability of atoms.

How did Niels Bohr's model of the atom address the issue of atomic stability?

Bohr used the concept of quantized energy to propose that electrons moved in fixed orbits or shells around the nucleus, maintaining atomic stability by emitting or absorbing energy when jumping between these orbits.

What principle of quantum mechanics contradicts the idea of fixed electron orbits in Bohr's model?

The Heisenberg Uncertainty principle states that it's impossible to know the exact position and trajectory of electrons in an atom, contradicting the fixed orbits in Bohr's model.

What is the significance of the quantum mechanical model of the atom proposed by Erwin Schrödinger?

Schrödinger's model introduced the concept of electron clouds in atomic orbitals, where the probability of finding an electron is the highest, and formulated the Schrödinger-wave equations to calculate energy levels of electrons.

How does the evolution of atomic theory reflect the scientific pursuit of understanding the world?

The evolution of atomic theory from Democritus to Schrödinger demonstrates a continuous scientific pursuit of deeper understanding, with each generation building upon and refining the ideas of their predecessors.

Outlines

00:00

🏀 The Evolution of Atomic Theory

This paragraph delves into the historical understanding of atoms, starting with Democritus' theory of 'atomos' in 400 BC, which posited that everything was made of indivisible particles. Aristotle later countered this with his four elements theory. The narrative then shifts to John Dalton in the 19th century, who introduced the law of multiple proportions and the theory of atomism, suggesting that atoms are unique solid spheres. Dalton's model was later challenged by J.J. Thomson's 'plum pudding' model, which depicted atoms as positively charged masses with embedded negative charges. Ernest Rutherford's gold-foil experiment led to the discovery of the nucleus, and Niels Bohr's model introduced quantized energy levels for electrons, though it was later found to be inconsistent with the Heisenberg Uncertainty principle.

05:01

🌐 Quantum Mechanics and the Modern Atomic Model

The second paragraph explores the advancements in atomic theory with the introduction of quantum mechanics. It discusses how Bohr's model, despite its popularity, was limited by its inability to account for the Heisenberg Uncertainty principle. Erwin Schrödinger's quantum mechanical model replaced the fixed orbits with electron clouds in atomic orbitals, where the probability of finding an electron is highest. Schrödinger's wave equations allowed for the calculation of electron energy levels, marking a significant shift from knowing where an electron is to understanding where it could be. The paragraph concludes by emphasizing the importance of continuous exploration and curiosity in understanding the fundamental structures of our world.

Keywords

💡Basketball

Basketball is a popular sport played with an orange spherical ball. In the video, it serves as an analogy to introduce the concept of atoms, highlighting how everyday objects can be used to understand complex scientific ideas. The script uses the basketball as a metaphor to pique curiosity about what's inside an object, leading to a discussion about the internal structure of atoms.

💡Atomos

The term 'atomos' comes from the Greek philosopher Democritus, who theorized that everything is made of tiny, indestructible particles called 'atomos,' meaning 'uncuttable.' This concept is foundational to the video's theme, as it sets the stage for the historical development of atomic theory. Democritus' idea that materials' properties depend on the type of atomos they are composed of is a precursor to modern atomic theory.

💡Aristotle

Aristotle was a prominent Greek philosopher who challenged Democritus' theory by proposing that everything is made of four elements: earth, fire, water, and air. His ideas were influential in discrediting the early atomic theory, as they dominated scientific thought for centuries. This is relevant to the video's theme as it shows the evolution of scientific understanding and the challenges faced by early atomic theorists.

💡John Dalton

John Dalton was a British chemist who is credited with developing the modern atomic theory. His experiments with gases led to the law of multiple proportions and the theory of atomism, which posited that everything is made up of atoms. Dalton's work is a pivotal point in the video, illustrating the scientific method and its role in advancing our understanding of atomic structure.

💡Law of Multiple Proportions

The law of multiple proportions, discovered by Dalton, states that when gases react with each other, they do so in fixed ratios. This law is crucial to the video's narrative as it provides empirical evidence supporting the atomic theory, showing that chemical reactions involve discrete units of matter, which are atoms.

💡Plum Pudding Model

The 'plum pudding' model, proposed by J.J. Thomson, describes an atom as a positively charged mass with tiny negative charges embedded in it, similar to plums in a pudding. This model is a key concept in the video as it represents a significant step in the understanding of atomic structure, although it was later disproven by Rutherford's gold-foil experiment.

💡Gold-Foil Experiment

The gold-foil experiment, conducted by Ernest Rutherford, involved firing alpha particles at a thin sheet of gold foil. The unexpected deflection of some particles led to the discovery that atoms have a dense, positively charged nucleus. This experiment is a turning point in the video, as it refutes the plum pudding model and leads to the development of the nuclear model of the atom.

💡Nucleus

In the context of the video, the nucleus is the central part of an atom, containing most of its mass and positive charge. Rutherford's gold-foil experiment demonstrated the existence of the nucleus, which is a fundamental component of the atomic structure. The concept of the nucleus is central to understanding atomic stability and the behavior of electrons.

💡Niels Bohr

Niels Bohr was a physicist who proposed a model of the atom where electrons orbit the nucleus in fixed paths or shells. His model was an attempt to explain atomic stability and the emission of radiation, which is a key theme in the video. Bohr's model, despite its limitations, is a significant step in the development of quantum mechanics and atomic theory.

💡Quantum Physics

Quantum physics is a branch of physics that describes the behavior of matter and energy at the atomic and subatomic level. In the video, quantum physics is introduced as a necessary framework to explain the stability of atoms and the behavior of electrons. It is crucial for understanding the limitations of Bohr's model and the development of the modern quantum mechanical model of the atom.

💡Schrödinger's Equation

Schrödinger's equation, formulated by Erwin Schrödinger, is a fundamental equation in quantum mechanics that describes the behavior of electrons in atoms. It is a key concept in the video as it represents the transition from Bohr's model to a more accurate quantum mechanical model. The equation helps predict the probability of finding an electron in a particular region around the nucleus.

Highlights

The concept of an atom dates back to 400 BC with Democritus' theory of 'atomos' - uncuttable particles that determine material properties based on their shape.

Aristotle's four elements theory challenged Democritus' atomic theory, proposing earth, fire, water, and air as the basic constituents of matter.

John Dalton's experiments with gases led to the law of multiple proportions and the revival of atomism, suggesting atoms as indestructible solid spheres.

J.J. Thompson's cathode ray tube experiment resulted in the 'plum pudding' model of the atom, with positive charge and embedded negative charges.

Ernest Rutherford's gold-foil experiment contradicted the plum pudding model, proposing a nuclear model with a concentrated positive center and orbiting electrons.

Niels Bohr introduced quantum physics to atomic structure, suggesting electrons move in fixed orbits or shells with quantized energy levels.

Bohr's model addressed the stability of atoms, explaining how electrons maintain energy levels without collapsing into the nucleus.

The Heisenberg Uncertainty Principle challenged Bohr's fixed electron orbits, indicating the impossibility of knowing exact electron positions and trajectories.

Erwin Schrödinger developed the quantum mechanical model, describing electrons as probability clouds in atomic orbitals rather than fixed paths.

Schrödinger's wave equations provided a method to calculate electron energy levels, enhancing our understanding of atomic structure.

The evolution of atomic models from Democritus to Schrödinger demonstrates remarkable scientific progress driven by curiosity and persistence.

The transcript emphasizes the importance of moving beyond general ideas to deepen our understanding of atomic structure through scientific inquiry.

Rutherford's nuclear model was a significant shift from previous atomic theories, laying the groundwork for modern atomic and subatomic physics.

Bohr's model, despite its limitations, remains a popular and educational representation of atomic structure in many textbooks.

The development of atomic theory highlights the iterative nature of scientific discovery, with each model building upon and refining its predecessors.

The transcript uses the analogy of a basketball's unknown interior to engage the reader and draw parallels to the historical unknowing of atomic structure.

The narrative encourages readers to embrace the spirit of exploration and inquiry, suggesting that curiosity can lead to significant scientific breakthroughs.

The historical progression of atomic models illustrates the dynamic nature of scientific knowledge, subject to revision and refinement over time.

Transcripts

When you think of the word “basketball”, what’s the first thing that comes to mind?

An orange sphere, probably, or perhaps your favorite athlete driving home a dunk.

Now, do you know what’s inside a basketball?

Have you ever seen the inside of one?

Even if you’ve never seen the inside of a basketball, you may have a general idea

about what you would find.

The same thing is true for atoms; generations ago, people didn’t know exactly what was

inside an atom, but they had some “ideas”.

Around 400 BC, a Greek philosopher named Democritus came up with a theory that everything in the

world was made of tiny indestructible particles called “atomos”, which means “uncuttable”.

He believed that the properties of materials depended on the type of atomos they were composed

of.

For example, sour or sharp-tasting things were made of particles with pointy edges,

sweet stuff was made of more rounded or smooth atoms, and metals were composed of hard atoms.

Apart from this shape misinterpretation, he was basically on the right track about atomic

composition dictating the properties of a substance.

However, this theory was largely discredited by Aristotle—the original social influencer,

who believed that everything on this planet was made of four elements: earth, fire, water,

and air.

The next step in atomic theory development didn’t happen for nearly 2000 years, when

British chemist and meteorology enthusiast John Dalton raised some interesting questions.

He conducted experiments wherein he mixed two gases and observed their behavior.

He noticed something rather curious when nitric oxide was allowed to interact with atmospheric

oxygen.

36 measures of pure nitric acid reacted with 100 measures of air to create 80 measures

of a new gas that was neither nitrous nor oxygenous.

This intrigued him quite a bit, so he conducted the same experiment with different volumes

of gas.

He observed that the gases reacted with each other, but only in a fixed ratio.

This gave rise to the law of multiple proportions and the theory of atomism.

Following his breakthrough, Dalton proposed that everything in the world was made up of

atoms—tiny indestructible solid spheres that were unique for every element.

Atoms of different elements combine to form different compounds and are rearranged during

chemical reactions.

More than two centuries of scientific development have passed since he first proposed that idea,

but some aspects of that model remain uncontested to this day.

Until the late 19th century, atoms were envisioned as indivisible particles, but that belief

was shaken by an English physicist named J.J Thompson and his trusty cathode ray tube.

Inside an almost vacuum glass tube, a visible beam of particles or cathode rays was generated

by applying high voltage across metal electrodes.

The stream of particles produced from the metal deflected away from the negative charge

and directed more towards the positive charge.

After repeating this experiment several times with other metals, he came up with the first

atomic model—the famous “plum pudding” model.

This model characterizes an atom as a particle that is composed of a positively charged mass

(the pudding), as well as tiny negative charges embedded in it (like plums).

After some initial resistance, this model became quite popular in the scientific world.

Even so, New Zealand-born Ernest Rutherford was not convinced.

It was the early 1900s, radioactivity was all the rage, and during his work on radioactive

decay, Rutherford discovered alpha, beta, and gamma rays.

He wanted to develop a method to detect alpha particles and use it to probe into the structure

of an atom.

He did what every physicist at the time did… he came up with an experiment!

The gold-foil experiment, also known as Geiger–Marsden experiments, consisted of a thin sheet of

gold foil with a circular Zinc Sulphide-coated screen behind it.

The screen would flash every time an alpha particle hit it.

Rutherford expected the particles to bullet through the foil and hit the screen behind

it.

While most of the particles did behave as expected, some were deflected at an angle

greater than 90 degrees.

Backed by his observations, he came up with a new atomic model that disproved the previous

one.

He proposed an atomic structure where most of the atom’s mass was concentrated in a

positively charged center (which he later named the nucleus) around which the electrons

orbited like planets around the sun.

A year after the publication of Rutherford’s atomic theory, Niels Bohr found a discrepancy

in the model.

If electrons were orbiting around a positively charged center, at some point those electrons

would lose their energy and collapse into the nucleus, thus making the atoms unstable.

However, that wasn’t the case, as atoms were generally quite stable, aside from the

radioactive ones.

This is where quantum physics comes into the picture.

He used the concept of quantized energy to propose that electrons moved around the nucleus

in fixed orbits or shells.

A shell closer to the nucleus has lower energy, while the one farthest away has the highest

energy.

If an electron jumped to a lower energy orbit, it would give out the extra energy in the

form of radiation, thereby maintaining atomic stability.

Even though Bohr’s model doesn’t hold true for complex multi-electron systems, this

model is still the most popular representation of atomic structure in most textbooks.

No matter how much we try, there is no avoiding the complexities of quantum mechanics.

With the establishment of the quantum behavior of entities like electrons, it became quite

clear that Bohr’s atomic model didn’t satisfy the Heisenberg Uncertainty principle.

According to this principle, it’s impossible to know the exact position and trajectory

of electrons in an atom, which means they can’t exist in fixed orbits, as Bohr hypothesized.

Combining the concept of wave-particle duality and the uncertainty principle, Erwin Schrödinger

came up with the quantum mechanical model of an atom.

In this model, the electrons did not revolve around the nucleus in circular orbits, but

rather as electron clouds in an atomic orbital, a region inside the atom where the probability

of finding an electron is the highest.

He also formulated the Schrodinger-wave equations that would help us accurately calculate the

energy levels of electrons in an atom.

This new and improved atomic model does not tell us where an electron is, but where it

could be.

Clearly, our understanding of “what’s inside an atom” has evolved remarkably over

the last few centuries, but it was only possible because having a “General” idea about

atomic structure simply wasn’t good enough for some people.

They dug deeper, often dedicating their careers and lives to their pursuit, and now we know

so much more about the stuff that makes up our planet.

With that in mind, if you feel curious and adventurous someday and want to know what’s

inside your basketball... you know what to do!