Scientific knowledge is continually evolving. Scientists are always researching, life is always evolving, and new things are being discovered every day. Generally speaking, scientific law describes a phenomenon, while the explanation of these phenomena are theories. Theories evolve with further research before becoming laws. As such, scientific knowledge continues to change in conjunction with the evolution of new research and new methodology. While at one point research may indicate that an increase in plant growth is dependent upon the addition of fertilizer, as researchers find better ways to manufacture better or different fertilizers, their products evolve too, sometimes for the better and sometimes for the worst. Not every type of research produces ideal results. Not every type of research aims to find a cure but sometimes to determine the cause.
Reproducibility is the ability of the results of an experiment to be closely replicated when the methodology of the experiment is performed again. If a particular experiment yields results that can not be reproduced again, the reliability of that study is obviously called into question . Thus, reproducibility is an important indicator of the accuracy and reliability of the methodology and results of an experiment.
Major Historical Developments
Major progress in regards to atoms was made in the late 19th century and led to significant strides in research after the end of the 19th century. English physicist J.J. Thompson’s experiment with cathode ray tubes ultimately led to discovering the presence of the subatomic particle electrons. Using an airtight glass tube with two metal electrodes, he would apply high voltage and a cathode ray would appear. Utilizing various metals for electrode composition, he noticed that a visible beam deflected away from the negative charge and toward the positive charge. Using this information, Thomson could calculate a charge-to-mass ratio of the particles and ultimately determine that the contributing particles were in fact much lighter than the atoms were. The observations lead to a rather controversial conclusion that these particles were attracted by positive charges and repelled by negative charges. This was the first indication that a negatively charged component existed as a fundamental part of the atomic structure.
In 1904, Thomson proposed a “plum pudding model” of the atom. This resembled negatively charged “plum” electrons found balanced within a positively charged “pudding.” This theory would later be disproved by a gold foil experiment and the work of Ernest Rutherford, Hans Geiger, and Ernest Mesden.
In the early 1900s, an American physicist by the name of Robert A. Millikan performed experiments where he utilized an oil atomizer to spray oil droplets into a sealed container. Here, he observed the oil landing on brass plates that were positively charged. From there, they traveled through a hole in the center of the plate, through x-rays emitted inside the container. This electrically charged the oil droplets, which finally landed on a negatively charged brass plate. He was then able to measure the charge of these oil drops and ultimately determine the charge of an electron. In conjunction with Thomson’s research, he could further determine the mass of an electron.
New Zealand Physicist Ernest Rutherford and his colleagues Ernest Marsden and Hans Geiger utilized a beam of positively charged alpha particles (α particles). They aimed beams of these α particles at a piece of gold foil and noticed that the α particles scattered. Ultimately, they found that a majority of the α particles passed through the foil and were not deflected while a very minute amount of particles were significantly deflected. What they concluded was that since the α particles passed through the foil without deflecting, they had to have traveled through a relatively vast amount of empty space. Furthermore, given the short amount of time the deflections occurred, a small positively charged body was likely centralized within the atom. This led to Rutherford’s proposal of an atomic structure with a positively charged nucleus where much of an atom’s mass is found, surrounded by electrons which yield a neutrally charged atom. It was not until the 1930s when James Chadwick pieced together that uncharged neutrons were also a part of the mass contained within the nucleus.
Around 1913, a man named Neils Bohr, a student of Rutherford’s in England, utilized both Planck’s theories of quantization and Einstein’s theory that light consists of photons with energy proportional to their frequency, and tested his own theory that an electron orbiting a nucleus would emit photons if it was found to be in a separate, orbiting plane. Bohr was able to derive the Rydberg constant, which lent support to his atomic model but accounted for only 1 electron and thus couldn’t broadly apply to all elements. Bohr was ultimately the first to discover that electrons travel in different orbits and not in a single plane. He further determined that the number of electrons varies from element to element and won the Nobel prize for his research on the atomic model.
Impact on Society and the Environment
The application of chemistry is all around us! From drinking treated water out of the facet in the morning, to taking any type of pharmaceuticals, eating any form of processed or cooked food, and putting gas into your car- you encounter chemistry at work daily. Many people accept today that chemicals like carbon dioxide, emitted from mankind’s interferences such as deforestation, and the burning of fossil fuels which contributes to global warming and the “greenhouse effect.” The decomposition of waste in landfills emits methane, another gas that contributes to global warming and environmental pollution. The maintenance of manure associated with livestock emits methane into the atmosphere while the combustion of fossil fuels and the manufacturing of commercial grade fertilizer all emit nitric oxide into the atmosphere. While chemistry research and advancements are making great strides in easing burdensome, everyday processes for us, these things don’t come without a cost. The effects of global warming may not be readily noticeable in the present tense, but they will be a problem humankind will encounter eventually. Mankind’s activities have devastating consequences on the Earth’s natural greenhouse and current global warming trends. Since the industrial revolution, humans have literally changed the composition of gases in the Earth’s atmosphere by emitting various pollutants into the environment from various processes. The presence of these gases in the atmosphere form acidic pollutants that cause acid rain.
Acid rain is an umbrella term for rainfall with unusually high acidic content or low pH levels. The term does not just apply to rain but can encompass sleet, fog, snow, hail, and other forms of precipitation. When chemical compounds are released into the air as a byproduct of human activity, they rise into the atmosphere and react with water and oxygen. Many chemical pollutants react readily with water and can then move great distances with the wind. This affects not only densely populated areas, but even areas seemingly unaffected by the pollution caused by mankind’s advancements in technology. If you think that because you don’t directly interact with one of these industries, you aren’t contributing to it, think again. Everytime exhaust comes from your vehicle, you’re emitting sulfur dioxide and nitrogen oxide into the environment. The use of electricity in your home comes from a power plant burning fossil fuels and releasing nitrogen oxide and sulfur oxide into the environment.
Chemistry makes virtually all forms of medical imaging possible. Sonograms use high-frequency sound waves to see inside human bodies. X-rays use electromagnetic radiation to create images of the human skeleton. Magnetic resonance imaging, or MRIs, use radio waves and very strong magnetic fields to create images of the human body for medical imaging. Computerized tomography, or CT images, shoot narrow beams of x-rays through the body. A specialized CT computer then takes digital x-ray detectors to create 2-dimensional images of the human body to create medical images for physicians to use for more reliable, modern diagnostic analysis.