chemistry - Chemistry just the basics please Why study...

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Chemistry: just the basics, please! Why study chemistry in a biology class? All energy comes from chemical reactions… therefore we carry out chemical reactions in our bodies constantly. Life is all about chemistry… Starting with the periodic table – a very organized way of displaying all of the elements. You can tell a lot about an element by looking at where it sits on the periodic table. Some definitions: - Elements: made up of only one type of atom. - Molecule: has more than one atom. An element can be a molecule (O2). - Compound: has more than one type of atom. H2O is a molecule and a compound. A compound will always have the same ratio of atoms for a particular compound.. that is, water will always be one oxygen and two hydrogen atoms. Once atoms become a compound, it requires a chemical reaction to get those compounds back - Mixtures: a substance from which you can reacquire the original compounds from the mixture with no chemical reaction; no set ratios (salt water could be 10% salt, or 1.3% salt, but it’s still salt water either way) 118 elements, but only 3 (C, H, O) make up 98% of the earth. Humans are mostly made of 4 elements: C, O, H, and N, with Ca and P coming in next in amount. Other important elements in the body are Na, K and Cl. (All of these are elemental symbols you should be able to recognize and identify) What is an atom? The smallest unit that can be defined as a particular substance… a C atom is the smallest unit of carbon… anything smaller is no longer carbon. Atoms made up of three smaller particles: neutrons (no charge), protons (positive charge), electrons (negative charge). In an atom with a neutral charge, the # of protons and electrons should be balanced (8+ and 8- is neutral). The atom generally has the “planetary model” shape… with a “sun” made of protons and neutrons, and “planets” circling are electrons. The proton is the particle that gives an atom its identity – element 1, hydrogen, has one proton (and because it is a neutral atom, also has one electron). Element 2, helium, has 2 protons and 2 e-. As long as an atom contains the same number of protons its identity will remain – so that helium atom will always be helium as long as it has 2 protons… it gains a proton and becomes Li… loses one, becomes H. An atom can, however, have a variable number of neutrons – usually the # is near the # of protons, but not always exactly the same. Protons and neutrons together make up the mass of an atom (the mass of e- is negligible). Isotopes – atoms of a particular element containing differing numbers of neutrons. For example C-12, 6 protons/6 neutrons (6+6=12): C-13, 6/7; C-14, 6/8. Naturally occurring carbon is a mixture of these three
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isotopes. Electrons: in a neutrally charged atom there will be equal numbers of protons and e-.
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