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Welcome to high-school chemistry class section two! This month contained some truly fascinating insights into the subatomic interactions of atoms to form molecules, more information on the Periodic Table of Elements, Lewis structures, and VSEPR theory. But before I get to these exciting topics, I'm going to summarize the structure of the atom, as it is fundamental to these other topics.

 

So far, we've learned that an atom is composed of protons, neutrons, and electrons and that the protons and neutrons are arranged in a tight bundle in the center, called the "nucleus," while the electrons whirl around the nucleus in orbitals of various shapes and sizes. Since the electrons are the furthest of the three particles from the nucleus, the electrons are the very first thing that other atoms encounter, which means they will determine the vast majority of its atom’s physical and chemical properties. Because of their importance in determining the properties of the atom, these electrons that are furthest from the nucleus are given a special name: "valence electrons.” Of course, since the number of electrons differs from atom to atom, each type of atom has its own set of properties that makes it unique from all the rest.

 

One more important detail we learned is that all atoms, regardless of their type, want to end up having the most valence electrons that they can. Because the orbitals furthest away from the atom’s nucleus can hold up to eight electrons – with several, notable exceptions – atoms will interact with each other in order to achieve this number of valence electrons. How these atoms interact with each other to attain eight valence electrons was the primary component of our class during this past month.

 

Other than learning about valence electrons and the formation of compounds, we also learned how to draw what are called “Lewis structures,” named in honor of Gilbert Lewis who first invented them at the University of California at Berkeley. Basically, Lewis structures are a helpful way to determine how atoms will form molecules together, and they consist of two, main parts. The first part is the central abbreviation of the atom of interest. For example, the abbreviation for the atom “carbon” is “C,” the abbreviation for “sodium” is “Na,” the abbreviation for iron is “Fe,” etc. Once the abbreviation is drawn, then the valence electrons are illustrated as small dots around the abbreviation in a clockwise manner. If, for example, an atom had five, valence electrons, then five, individual dots would be arranged in a specific pattern around the atom. These Lewis structures are extremely useful to chemists in that it lays out how atoms form molecules in such a way that makes the thought processes involved easier to complete and less prone to result in mindless errors.

 

Simply knowing how atoms interact to form molecules and how to illustrate this process, though, isn’t enough information to determine the final shape and structure of the molecule. This has to be determined by what we’ve been learning about called the Valence Shell Electron Pair Repulsion (VSEPR) theory. That’s a really big name, for sure, but it is deceptive since the concept behind it is quite simple. What this theory suggests is that the valence electrons of the central atom in the molecule don’t want to be near each other. This is a reasonable assumption since electrons all have the same, negative charge, and since similar charges repel one another. Because of this valence electron repulsion, a wide array of molecule shapes and structure are formed from atoms and the arrangement of electrons in these atoms.

 

Also during the past month, the Periodic Table of Elements, shown simplistically at this website, was studied closer, and several properties of all atoms were shown to be related to where an atom is located on the Table. Because the magnitude and extent to which these properties relate to the atom in question depends on its location on the Table – and because their affect changes regularly from atom to atom as you move up, down, right, or left on the Table – these properties are known as “Periodic Properties” and are what make the Table such an incredible resource for chemists.

 

Upcoming material in our chemistry class includes the study of covalent and polar bonds, acids, bases, indicators, amphiprotic compounds, exothermic and endothermic reactions, molarity, solutes, solutions, and solubility. That’s definitely going to be a challenge, but when you realize that we’ve got a whole month to cover it, it doesn’t seem all that difficult. Right now we’re all busy preparing for the exam covering all the material of our first semester, and we’ll have to wait until that exam has come and gone before digging into the amazing concepts that await us.

 

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