Introduction to Chemical Bonding and Biology Help
Introduction to Chemical Bonding and Biology
A chemical bond is the sharing or transfer of electrons between the outer surface clouds of atoms. And Figure 2.2 depicted a C–C (carbon–carbon) bond. The carbon atom nuclei were represented as two gumballs, each surrounded by a sticky electron cloud of cotton candy. The bond resulted when the clouds were smashed together, then slightly pulled apart.
Bonds And Order
Picture in your mind groups of three or more atoms held together by chemical bonds. Do you see triangles or other simple geometric patterns? In a functional sense, chemical bonds are builders of order. They are builders of order or pattern at the chemical level of biological organization. Consider two specific examples – a water (H 2 O) molecule (Figure 4.1) and a sodium chloride (NaCl) crystal.
The water molecule is shaped like a triangle or V, with the O (oxygen) atom at the tip or apex. A hydrogen (H) atom is attached on each side by a covalent (koh- VALE -ent) bond, one which involves a sharing of outermost electrons between atoms. Since the larger oxygen atom draws each of the electrons from the hydrogen atoms into closer orbit around itself, positive and negative poles are created. The O end is the negative pole (having an excess of two negatively charged electrons), while each H end makes up a positive pole. The H ends of each bond create a positively charged pole, because their electron has been unequally shared with the oxygen. In effect, the oxygen atom is an “electron hog”! It still leaves each electron-robbed hydrogen atom with its positively charged proton, however.
Now let us consider the salt crystal (Figure 4.2). Numerous sodium (Na) and chlorine (Cl) atoms combine with one another to form a beautiful cube-shaped solid. This precise geometric pattern is seen in common table salt. (Think of this when you are eating your salted pretzels or French fries!) Each face of the salt cube is a square, with alternating Na + and Cl – ions ( EYE -ahns) at its corners. An ion is an atom that has either a net excess or deficiency of outermost electrons, such that it is electrically charged. The sodium ion, for instance, is symbolized as Na + , because it has a deficiency of one electron. Where did this electron go? It was transferred from the outer cloud of the Na atom, and onto the cloud of the Cl atom. The result is an ionic bond – a bond that results from the transfer of one or more electrons between atoms. And since the chlorine atom (Cl) picks up that extra electron being transferred from sodium, it becomes a chloride ion , Cl – , having an overall negative charge.
Thus we see that there are two main types of chemical bonds – covalent bonds and ionic bonds. Covalent bonds result from the sharing (either equal or unequal) of outermost electrons between atoms, while ionic bonds arise from the complete transfer of one or more outermost electrons between atoms. In either case, the result is an increase in the state of order or pattern of the atoms involved. In particular, note from Figure 4.2 (above) the elegant crystal lattice ( LAT -is) or layered network pattern of the NaCl cube.
Recall that carbon dioxide (CO 2 ) is considered an organic molecule, because it contains a carbon (C) atom. Conversely, both the H 2 O molecule and the NaCl crystal are inorganic compounds, because they do “not” (in-) contain any carbon. Long chains of hydrocarbon molecules contain numerous C–H (carbon–hydrogen) covalent bonds. Due to the fact that each carbon atom can form covalent bonds with other carbon atoms (as well as with H atoms), it can create extremely long, highly orderly, C–C chains. Such long organic chains form the stable “backbone” of many macromolecules (like DNA and proteins), as well as that of larger body structures.
Practice problems for these concepts can be found at: Chemical Building Blocks Test
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