Geo331 lect2 - Lecture 2 Chemistry and Geology Refresher I...

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Lecture 2: Chemistry and Geology Refresher I. Chemistry 1. The Atom Atomos means "indivisible" in ancient Greek (a=not, tomos=divided). The concept of atoms and elements are closely linked. An element cannot be broken down into simpler substances by ordinary chemical or physical means. Rust, iron oxide, can be broken down into iron and oxygen, but iron cannot be broken down into anything simpler. An atom is the smallest particle that retains all of the properties of an element. Atoms combine (bond) together to form compounds. Most minerals (and gems) are chemical compounds. The chemical and physical properties of minerals is tied to the atoms within their structure. The nucleus is at the center of the atom, where most of the mass of an atom lies. Protons and neutrons lie within the nucleus (by convention, protons and neutrons each have a mass of 1). A proton has an electrical charge of +1, while a neutron (as the name indicates) has no charge. The electrical charge of protons is additive so that two protons have an electric charge of +2, four protons have a charge of +4, et cetera . Surrounding the nucleus is a cloud of electrons . An electron has negligible mass compared to the nucleus, but it has a charge of -1 (exactly opposite of a proton). In normal atoms, the number of protons and electrons is the same: the net electric charge of an atom is zero. In 1912, Danish physicist Niels Bohr proposed an atomic model where each electron orbited a set distance from the nucleus. Instructors often use this model as an introduction students to the atom - understanding chemical reactions and atomic bonds is relatively straightforward and simple to represent graphically, but it doesn't work for anything more than that. Modern models of the atom place electrons in a region of probability - a place where they are most likely to be found. This is represented by fuzzy clouds surrounding the nucleus. This is more accurate, but it can be harder for the non-scientist to grasp. For this class we will think of atoms (and their constituent particles) as solid spheres of varying sizes. This allows us to think of atoms as small building units of larger structures and see the difference between atoms. 2. Elements: The periodic table is, stated simply, a list of all the different kinds of atoms there are. Elements are merely these atoms, each with it's own chemical and physical properties. Each element has a different number of protons in the nucleus. For example, Hydrogen (element symbol: H) has one proton in its nucleus. Helium (He) has two, Lithium (Li) has three, and so on. There are 92 naturally occurring elements and about another 25 that have been artificially created in the lab. While it's not important to know all 92 elements and their abbreviations, you will be responsible for knowing ten of the most common elements in the earth's crust (which are often found in gems): Oxygen [O] (most common), Silicon [Si], Aluminum
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[Al], Iron [Fe], Calcium [Ca], Sodium [Na], Potassium [K], Magnesium [Mg], Titanium [Ti], Hydrogen [H], Phosphor [P].
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