Lecture2 Note

Lecture2 Note - Wed 8.5.09 Lecture 2 Chemical Foundations...

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Wed. 8.5.09 Lecture 2: Chemical Foundations of Life I. The Chemical Components of a Cell Matter, Element, and Atom o Matter is made of combination of elements , such as Hydrogen, Oxygen, or Carbon o Atom is the smallest particle of an element. o Atoms are linked together in groups to form molecules . All the characteristics of a cell depend on the molecules it contains. Structure of an Atom o Most of the weight of the atom comes from nucleus. o Electrons contribute insignificant amount to the total weight of an atom. o Why are there electrons moving around? To balance out the charge. Mole o A mole is X grams of substance, where C is its relative molecular mass (molecular weight). A mole will contain 6x10^23 (Avogadro’s number) molecules of the substance. o Molar solutions have concentration of 1 mole of the substance in 1 liter of solution. C,H,O and N Constitute 99% of Total Atoms in the Human Body o Why is that? Stable These for elements can make covalent bonds. (others don’t) The outermost electrons determine how atoms interact. o In order for an atom to be stable, the outermost shell must be filled completely. o When the outermost shell is not completely filled, the atom is unstable, therefore chemically reactive. Atoms can donate, accept, or share electrons to fill its outer electron shell and make them stable o Covalent bond – sharing of electrons o Ionic bond – transfer of electron o Covalent bond is more stable because there is no partial charge o Covalent bonds are much stronger and more stable than non-covalent interactions o Depending on the environment, an ionic bond may be stronger than hydrogen bond. 1
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The precise orientation of covalent bonds forms the basis for the 3-D geometry of the organic molecules in a cell. o The 3-D geometry formation is due to lone pair. o Electrons have same charge there for repulsion occurs (electron repulsion) to form a geometric formation that is most stable. Stereoisomer o Have the same components but are not the same. They are the mirror image to each other. (like hands… Cannot overlap) o They have similar chemical properties but distinct biological properties. Single Bond vs. Double Bond o Double bond is more rigid and shorter when compared to the single bond. o Double bond cannot rotate freely due to the presence of the p orbital. (P orbital is perpendicular to the sp-orbital) Different types of covalent bonds: polar vs. non-polar o O2 is non-polar because they have the same ability to attract the electrons, therefore the shared electron maintain the same distances between the molecules. o Water is polar due to the difference in the electro negativity between oxygen and hydrogen. o Oxygen has more electro negativity when compared to hydrogen; therefore the shared electron is closer to the oxygen atom.
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