Chemistry is the study of matter and the changes that it undergoes. Since all matter consists of atoms, it is important that you understand the atom and its components especially the electron.
Why the electron? Because the electron configuration determines how an element will behave in chemical bonding and chemical reactions. So if you understand the electron you will better understand chemistry.
However, you must keep in mind that the atom and its components are so small that scientists are unable to work directly with the atom. Therefore, chemists and physicists need to create models to aid in the description of the atom. But, a scientific model is limited to the information available at the time it is created. So, when new experiments lead to new discoveries the model must be changed or discarded.
Despite the fact that scientific models change, models are the only way man has to describe how several natural phenomena work. And knowing how a process functions is often crucial to further scientific discovery. So, models are not truth, models are man's best estimates at how things work. For that reason, the importance of models is not their truth, but their workability.
Remember that models are created by humans and can have biases, flaws and inaccuracies. Always examine models in the light of the scientific method and be willing to discard that which doesn't measure up.
Although models are not perfect there are five models of the atom that lead to the understanding of matter. The more you understand these models the better you will be at chemistry. The five models are:
- The Solid Sphere model
- The Plum Pudding Model
- The Nuclear Model
- The Bohr Model
- The Wave Mechanical Model
Solid Sphere Model
The solid sphere model was proposed in 1803 by John Dalton. John Dalton was an English chemistry and math tutor who took the ideas of his day and put them into a model of how matter was arranged. He stated that matter was made of tiny indivisible particles called atoms and atoms of the same element were all alike. Also, he included the law of multiple proportions and the law of definite composition in his model. Although his model was not perfect it was the main main model for over 90 years.
In 1897 English physicist, J. J. Thomson, suggested that cathode rays consisted of negatively charged particles even smaller than atoms. As a matter of fact he suggested these particles were subatomic parts of the atom. Thus, Dalton's theory of an indivisible particle was no longer workable. A new theory that allowed for subatomic particles was needed.
So, Thomson proposed that the atom was a mass of positive charge with negative electrons placed into it like raisins in a pudding, and dubbed it the Plum Pudding model. Thomson's model, although attractive, nevertheless had many shortcomings.
The Nuclear Model
In 1906 Ernest Rutherford and his assistants, performed the famous Gold Foil experiment that led to the discoveries of the atomic nucleus and that the atom is mostly space.
The Gold Foil experiment demonstrated that the mass of the atom was the same as predicted by Thompson's model, but the volume of the mass was much smaller and seemed to be located in the center of the atom. Thomson's Plum Pudding model was no longer workable. So, in 1911, Rutherford proposed the Nuclear model of the atom.
The Bohr Model
In 1913 Danish physicist, Neils Bohr, suggested applying the quantum theory to the Rutherford model. Bohr's new model proposed that electrons are in fixed energy levels he called orbits. The energy of these orbits is quantized and electrons must absorb or release energy (photons) at certain wavelengths to move between energy levels.
The Wave Mechanical Model
In 1921 Louis de Broglie stated, without any empirical evidence, that if waves have matter properties then matter should have wave properties. Later, Bell Laboratories would prove that De Broglie's hypothesis was indeed correct. De Broglie's hypothesis was a revelation that even impressed Einstein and changed the view of the atom forever.
Combining Louis de Broglie's hypothesis with Bohr's model, Erwin Schrodinger proposed the electron was a 3-D waveform circling the nucleus in a whole number of wavelengths allowing the waveform to repeat itself as a stable standing wave representing the energy levels of the Bohr model.
In support of his hypothesis, Schrödinger developed a mathematical equation to describe the wave-like behavior of the electron. The Schrödinger wave equation not only gave the correct energy levels for the hydrogen atom, but also was somewhat useful in atoms with more than one electron. This mathematical description of the details of atomic behavior became known as the “Wave Mechanical Model".
The atom as we see it today is mostly space with a centrally located, very dense small nucleus containing positively charged protons and neutrally charged neutrons with negatively charged electrons placed in energy levels within the atomic space
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