If we compare an atom with a Kiwi fruit, the concentrated center portion can be compared to the positively charged atomic nucleus and the black color seeds to the negatively charged electrons. It was believed that these electrons revolve around the nucleus as the earth and the other planets revolve around the sun. As we know, atom is the smallest particle of an element and none can see the movement of these electrons with naked eye. The nucleus has two types of sub atomic particles, the positively charged protons and the neutral neutrons The above given concept of a mature nucleus and obedient electrons that maintain a regular and normal path was proposed by the Danish scientist Niels Bohr.
In 1922, Bohr received Nobel prize for proposing this atomic structure that laid the foundation for quantum physics. But do you think, the passive and obedient electrons and silent nucleus can generate the radioactivity? They will live together happily thereafter, don't they? But the reality is the tremendous energy of radio activity. The mighty alpha rays, beta rays, gamma rays, X rays and ever moving quarks and neutrinos are the truth. What contributes these invincible phenomena? When Bohr's atomic structure could not explain these phenomena, scientists came up with several ideas including electrons moving in same circular orbits but in different directions. Among them Louis De Broglie borrowed Einstein's wave theory of light and explained that all forms of matter like protons, electrons, atoms, molecules show dual character like light. de Broigle,by using Maxwell's electro-magnetic wave theory formulated the concept of matter waves. Matter waves are waves associated with moving microscopic particles.
Let's go back to the Kiwi fruit to understand the concept. In the image, you must have seen the tender flesh spread around the black seeds. Imagine, these tender layers are path of those seeds that moves in and around and the tender layers are formed because of the movement of those seeds. Instead of forming round path, the path formed by the seeds are like waves. Similar is the case with the path of electrons around the nucleus. These path of electrons around the nucleus are called orbitals. Orbitals are regions in space around the nucleus where electrons are likely to be found.
Now, let's understand why scientists were worried about the structure of atom in terms of radioactivity. What is radioactivity? Radioactivity is the emission of radiation or particles caused by the disintegration of atomic nucleus. Alpha particles positively charged particles that consists of two protons and two neutrons. Beta particles are negatively charged and is generated by the nucleus during its disintegration process, whereas gamma rays are neutral radiation. If the Bohr Atom model was correct, an atom always will have a stable nucleus with same number of protons survived by same number of obedient electrons moving around it in a desirable velocity.
The disintegration of nucleus indicated the possibility of charge difference and growing tension within the nucleus. The primary reason could be the mismatch in the charge and that led the discovery of wave theory of sub atomic particles. This concept led Werner Karl Heisenberg to formulate a principle about the location of electrons within the atomic orbitals named Hesenberg's uncertainty principle. Heisenberg stated that "It is not possible to determine simultaneously and precisely both the position and momentum of a microscopic moving particle like electron, proton etc." According to the uncertainty principle, due to the wave nature of electron, we cannot describe the exact path i.e., position followed by an electron at any time. Thus Bohr's theory, according to which electrons are regarded as having fixed position of definite energy, is no longer correct.
How does it affect the human beings if we believe that Bohr Model of atom is the correct model and shut all the further research based on wave theory? If the scientists did not explore the truth behind the atomic structure,
1. We would never have been able to treat cancer patients
Gamma rays are used to kill off cancer cells and is used for cancer treatment. The atom of the element Cobalt-60 is commonly used for this purpose. Utilizing radiation to combat cancer is an important career. With the growing rate of cancer cases in the world, a degree in radiation therapy reckons a lot of opportunities.
2. Killing Microbes
Gamma rays are successfully uses to destroy microbes that cause food to decay. Surgical instruments and syringes can also be treated with gamma rays. It is a great way to prevent infections been transferred.
3. Carbon Dating
When an animal or plant dies it stops taking in carbon. But its carbon-14 content continues to decay. If we compare the carbon-14 with that from a living thing, the age of animal and plant remains can be calculated. This is known as carbon dating. Carbon dating is used in the study of fossils. It is also a great career that has opportunities in the disciplines of archaeology, paleontology etc,
4. Calculating the age of rocks
1.2% of the remaining potassium atoms is radioactive, known as K-40. The nucleus of this atom disintegrates for twelve thousand years and eventually decays to form the stable argon atom. By tracing the argon content of potassium rocks, scientists can calculate the age of such rocks. Therefore, it is a great support for geologists and geographers.
Learning Chemistry in general and about atoms and molecules in particular with an eye for details is a great achievement. So, I suggest all of you to read and understand it.