It is Spring break, and I am relaxing a bit after my mock exams. COVID-19 and lockdown are still there, but I hope that by the time I write my IGCSE exams, the situation becomes better.
Atomic Physics is one of the last chapters in my IGCSE Physics book. I have been reading about atoms since middle school and Bohr’s model with the nucleus at the center and electrons revolving around it was quite easy to understand. But it is not so simple as it appears to be. According to Prof. Andy Parker of Cambridge University, Physics has a problem with small things, especially infinitely small things, and the quest to find the smallest things remains incomplete. The arrangement and movement of the electrons are a bit more complex than those explained by the planetary model. We now know that the protons and neutrons that make up the nucleus are further made of quarks. A fundamental particle like Higg’s boson has also been produced at the large Hadron Collider. I am also perplexed by the kind of forces that operate inside the atom.
I wish I could step into this soooo.. tiny atom and understand how complex the entire world of the atom could be. That is the irony and beauty of atomic physics. No one has seen the atom structure actually and our understanding is based on mere speculation. But it is not based on baseless whims and fantasies of the scientists. The concept of the scientific method that I studied early in my science class makes a lot of sense now. It can guide a curious mind into solving a problem through a logical stepwise process of making an observation -> giving a possible testable explanation and creating a hypothesis -> experimenting and testing a hypothesis -> creating laws by repeated observations -> proposing a theory (the answer ‘why’) as the best possible understanding based on experiments and observations. Theories are closest to truths.
How complex is the structure of the atom?
The evolution of atomic theory over the years is based on the fundamental steps of scientific theory. Scientists like Dalton, J.J Thompson, Rutherford investigated the questions and experimented repeatedly to propose various theories. Whenever an existing theory cannot explain some observation, a new one is proposed.
John Dalton proposed the atomic theory that matters consist of atoms and that a given element consists of identical atoms.
J.J Thompson conducted the cathode ray tube experiment discovering the electron. He proposed the ‘plum pudding’ model for an atom where negatively charged electrons are dispersed like plums through the rest of the positively charged ‘pudding’ area of the atom.
E. Rutherford then tested Thompson’s ‘plum-pudding’ model. His gold-foil experiment failed the prediction or hypothesis that the alpha particles would not be deflected by the sparsely distributed positive cloud (pudding) of gold atoms. Based on experiments and observations, he proposed a new theory. The positive charge is not distributed throughout but rather concentrated in the atom’s tiny core called the nucleus. I remember reading in my physics book how the alpha particles bounced at the center in Rutherford’s experiment.
Niel Bohr dismissed Rutherford’s planetary model where electrons revolved around the nucleus in circular orbits of arbitrary radii. This was based on his observation of the spectral series of light emitted by hydrogen atoms. He proposed the theory that electrons are present in discrete radii, each orbit or energy level is labeled by the quantum number ‘n’ to explain the discrete wavelengths emitted by the hydrogen atom and why atoms emitted light of specific energy when heated. He explained that electrons moved up and down these energy levels by absorbing or emitting a quantized amount of energy. The concept of electrons moving in definite circular orbitals with fixed levels of energy was based on both classical physics and the quantum theory of radiation. This also explained why the electrons in the planetary motion do not eventually spiral into the nucleus.
But Bohr’s model could not explain the electronic structure of atoms containing more than one electron. The modern model was then explained using Quantum Mechanics.
How Quantum Mechanics explains atomic complexities?
Quantum mechanics explains the behavior of atomic and sub-atomic particles. It shows that all electromagnetic radiations exist as discrete units ‘photons’ or quantum. At sub-atomic level behavior of matter is strange and electrons seem to be spread out throughout the atom and behave both like a wave and a particle. So, the tiny atom’s behavior seems to be a bit complex now. Even Bohr agreed to it- “Anyone who is not shocked by quantum theory has not understood it.”
Further, De Broglie gave the hypothesis that particles could have wavelike properties and gave an equation where the wavelength and particle mass are inversely proportional (I need to read more on this after finishing off grade 10 exams). That is the probable explanation of why macroscopic objects do not show wavelike behavior.
Erwin Schrödinger used Broglie’s idea to give the modern quantum mechanical model of atom. The problems due to Bohr’s model where electrons existed as particles in defined orbits were solved by Schrödinger’s theory that the behavior of electrons within atoms could be explained by treating them mathematically as matter waves. Like any standing wave of a string instrument, the vibrations are quantized i.e will have only certain allowed wavelengths. Schrodinger gave an equation that led to the concept of atomic orbitals- the region where electron is likely to be 90% of the time.
Werner Heisenberg gave the Uncertainty principle stating that both the position and the velocity of an object cannot be measured exactly at the same time. This was against Bohr’s model where electrons moved in orbitals of a certain radius at a certain velocity. Such uncertainties are observed only at the atomic level and not at macroscopic levels.
Thus, Bohr’s classical model of electrons moving in orbits was replaced by a quantum mechanical model where electrons are in high probability areas called orbits. The orbitals can be explained using quantum numbers or energy levels or shells and their shapes.
I seem to understand some but not all of the complexities of atomic structure. A better understanding of equations given by De Broglie and Schrödinger, the application of the uncertainty principle, and a detailed study of quantum numbers should give me a better picture. That will be my homework for perhaps a more detailed blog on this topic.
How big is the potential of the tiny atom?
The capabilities and potential of the tiny atom are not so tiny 😊. Atomic Physics finds many applications of Quantum Physics. For example; Electron Microscope uses a beam of electrons to create an image. Nuclear Physics for example finds applications in the field of medicine, nuclear power, agriculture, geology, and archaeology. Two of the important areas of application are stated below.
Medicine
Radiation or radioactivity from atoms is used for about one-third of procedures in modern hospitals. Nuclear medicine is used in diagnosing and treating illnesses. X-rays, Ultrasounds, MRI scanners all use nuclear science. Radioisotopes like iodine-131 is used as a tracer to detect thyroid problems. Radiations emitted are captured by a gamma camera. A nuclear medical imaging technique like Positron Emission Tomography (PET) is used to produce 3-D images of functional processes of the body. Similarly. A technique like Magnetic Resonance Imaging (MRI) is used to see internal organs of the body.
Nuclear Energy
Huge amount of nuclear energy is produced by fission and fusion like processes of atoms.
Fission is the process of splitting a large, unstable nucleus of atoms (eg, Uranium-235) into smaller particles, thereby producing large amounts of energy. The neutrons produced during the reaction bombard other atoms and set up a chain reaction that produces enormous amounts of energy. The process is used to produce energy in nuclear reactors. It is also used to produce nuclear weapons like atomic bombs. Imagine how the same process that has the capacity to generate enormous energy to produce electricity is capable of destroying places like Hiroshima and Nagasaki !!
Nuclear Fusion is the process of small nuclei joining to produce a different element. This is the process that creates the energy of all the stars like the Sun. It creates far more energy than that produced by the fission reaction. Scientists have found it hard to replicate it as the process requires very high temperature and pressure. Someday, it could become a source of abundant, clean, and safe energy.
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