Draw a lewis structure for each of the following

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Draw a Lewis structure for each of the following formulas: a. phosphine, PH 3 (used to make semiconductors) b. hypochlorous acid, HOCl (used to bleach textiles) c. CFC‑11, CCl 3 F (used as a refrigerant) d. C 2 H 2 , acetylene (burned in oxyacetylene torches) Solution a. Phosphorus atoms usually have three covalent bonds and one lone pair, and hydrogen atoms have one covalent bond and no lone pairs. The following Lewis structure for PH 3 gives each of these atoms its most common bonding pattern. P H H H b. Hydrogen atoms have one covalent bond and no lone pairs, oxygen atoms usually have two covalent bonds and two lone pairs, and chlorine atoms usually have one covalent bond and three lone pairs. H O Cl c. Carbon atoms usually have four covalent bonds and no lone pairs. Fluorine and chlorine atoms usually have one covalent bond and three lone pairs. The fluorine atom can be put in any of the four positions around the carbon atom. C Cl Cl F Cl d. Carbon atoms form four bonds with no lone pairs, and hydrogen atoms form one bond with no lone pairs. To achieve these bonding patterns, there must be a triple bond between the carbon atoms. C H C H
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Molecular Shape Lewis structures are useful for showing how the atoms in a molecule are connected by covalent bonds, but they do not always give a clear description of how the atoms are arranged in space. For example, the Lewis structure for methane, CH 4 , shows the four covalent bonds connecting the central carbon atom to the hydrogen atoms: H H H H C However, this Lewis structure seems to indicate that the five atoms are all located in the same plane and that the angles between the atoms are all 90 ° or 180 ° . This is not true. The actual shape of a molecule can be more accurately predicted by recognizing that the negatively charged electrons that form covalent bonds and lone pairs repel each other. Therefore, the most stable arrangement of the electron‑groups is the molecular shape that keeps the groups as far away from each other as possible. The best way to keep the negative charges for the four covalent bonds in a methane molecule as far apart as possible is to place them in a three‑dimensional molecular shape called tetrahedral, with angles of 109.5 ° between the bonds. C H H H H The shaded shape is a regular tetrahedron. The angle formed by straight lines (representing bonds) connecting the nuclei of three adjacent atoms is called a bond angle . Three ways to represent the methane molecule are shown in Figure 3.10. The first image, a space‑filling model , provides the most accurate representation of the electron‑charge clouds for the atoms in CH 4 . A ball‑and‑stick model , the second image, emphasizes the molecule’s correct molecular shape and shows the covalent bonds more clearly. The third image, a geometric sketch , shows a simple technique for describing three‑dimensional tetrahedral structures with a two‑dimensional drawing.
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  • Fall '06
  • Mark
  • Atom, atoms, Chemical bond

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