{"id":66,"date":"2025-04-29T02:04:44","date_gmt":"2025-04-29T02:04:44","guid":{"rendered":"https:\/\/pressbooks.hcfl.edu\/introchemlabmanual\/chapter\/__unknown__-8\/"},"modified":"2026-04-21T15:21:47","modified_gmt":"2026-04-21T15:21:47","slug":"__unknown__-8","status":"web-only","type":"chapter","link":"https:\/\/pressbooks.hcfl.edu\/introchemlabmanual\/chapter\/__unknown__-8\/","title":{"raw":"Introduction to Molecular Modeling","rendered":"Introduction to Molecular Modeling"},"content":{"raw":"
\r\n\r\nhttps:\/\/youtu.be\/QVYCUf1RJCM\r\n
\r\n

Learning Objectives<\/p>\r\n\r\n<\/header>\r\n

\r\n
    \r\n \t
  • Use the chemical formula to draw the Lewis Structure for a compound and predict the molecular geometry.<\/li>\r\n \t
  • Apply the safety rules in the chemistry laboratory through proper and safe handling of chemicals and chemical equipment.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
    \r\n
    \r\n
    \r\n
    \r\n
    \r\n
    \r\n
    \r\n
    \r\n
    \r\n
    \r\n

    We will focus on molecules and polyatomic ions that have single, double, or triple bonds and one central atom, which is the atom bonded to all the others. The main goal is to practice drawing Lewis structures\u2014two-dimensional diagrams that show bonding and lone pairs of electrons\u2014predicting electron geometry, which describes the arrangement of regions of electron density around the central atom, and predicting the molecular shape, which is the actual arrangement of atoms in space. You will also estimate bond angles; the angles formed between bonds originating from the same atom.<\/p>\r\n

    To accomplish this, we use the VSEPR Theory (Valence Shell Electron Pair Repulsion Theory), which states that electron regions repel each other and arrange themselves as far apart as possible. Key concepts include understanding a Lewis structure, which shows all the valence electrons in a molecule or ion; electron geometry, which considers both bonds and lone pairs; molecular shape, which focuses only on the atoms; and bond angles, which describe the spacing between bonds. Knowing molecular shape is critical because it directly impacts chemical behavior. For example, water\u2019s bent shape makes it polar, giving it its remarkable ability to dissolve many substances, while carbon dioxide\u2019s linear shape makes it nonpolar despite having polar bonds. Even biological processes like enzyme function rely on molecules fitting together with precise shapes, much like puzzle pieces. Whether in chemistry, medicine, engineering, or even cooking, understanding molecular structure is key, because shape controls function.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n<\/article><\/div>\r\n<\/div>\r\n<\/div>\r\n<\/div>\r\n

    Let's practice building a model with a simple molecule: CO2<\/sub> (carbon dioxide). We must first draw the appropriate Lewis structure to model.<\/p>\r\n

    Step 1: Find the total number of valence electrons.<\/p>\r\n\r\n

      \r\n \t
    • \r\n

      The carbon atom contributes 4 valence electrons and each oxygen atom contributes 6 valence electrons to the overall structure. Therefore, this structure contains a total of 16 valence electrons available for bonding:\u00a0 \u00a04 + (6\u00d72) = 16 electrons.<\/p>\r\n<\/li>\r\n<\/ul>\r\nStep 2: Arrange the skeletal structure of the molecule.\r\n

        \r\n \t
      • \r\n

        Less electronegative atoms are central & more electronegative atoms are placed terminally. In this molecule, the carbon (C) atom will be in the center because it is less electronegative than oxygen.<\/p>\r\n<\/li>\r\n \t

      • \r\n

        Arrange the two oxygen (O) atoms on each side of the carbon atom. While more electronegative atoms are always placed terminally, we must also consider symmetry when building these molecules. Placing one oxygen atom on each side of the carbon allows the oxygen atoms to be both terminal and for the molecule to be most symmetrical in this setup, which allows for a more energetically favorable molecule.<\/p>\r\n<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_133\" align=\"aligncenter\" width=\"93\"]\"This Image generated by OpenAI\u2019s DALL\u00b7E.[\/caption]\r\n\r\nStep 3: Connect atoms with single bonds.\r\n

          \r\n \t
        • Single bonds should be placed between the central atom & each terminal atom. Account for the number of additional electrons used through the distribution of single bonds.<\/li>\r\n \t
        • 16 valence electrons - 4 electrons (2 single bonds) = 12 valence electrons remaining<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_135\" align=\"aligncenter\" width=\"105\"]\"This Image generated by OpenAI\u2019s DALL\u00b7E.[\/caption]\r\n\r\nStep 4: Distribute the remaining electrons on the outer atoms.\r\n
            \r\n \t
          • \r\n

            All remaining electrons should be distributed on the outer atoms first to make octets on each outer atom until all electrons have been exhausted. If electrons are remaining after each outer atom has an octet, leftover electrons may be dispersed on the central atom.<\/p>\r\n<\/li>\r\n \t

          • For carbon dioxide shown below:<\/li>\r\n<\/ul>\r\n16 valence electrons - 4 electrons (2 single bonds) -12 electrons (distributed in pairs on the oxygen atoms) = 0 remaining electrons\r\n\r\n[caption id=\"attachment_138\" align=\"aligncenter\" width=\"111\"]\"The Image generated by OpenAI\u2019s DALL\u00b7E.[\/caption]\r\n\r\nStep 5. Evaluate your structure for stability.\r\n

            In the above structure, each oxygen atom has an octet (3 lone pairs & 1 bonded pair), but the carbon atom does not have a full octet. To ensure that carbon has a full octet, form double bonds with each oxygen and reevaluate the stability.<\/p>\r\n\r\n<\/div>\r\n\r\n[caption id=\"attachment_142\" align=\"aligncenter\" width=\"108\"]\"This Image generated by OpenAI\u2019s DALL\u00b7E.[\/caption]\r\n\r\nOnce you have drawn the correct Lewis structure, you can build your model! Based on the Lewis structure above, the corresponding ball & stick model for carbon dioxide would look like:\r\n\r\n[caption id=\"attachment_571\" align=\"aligncenter\" width=\"160\"]\"Ball Image generated by OpenAI\u2019s DALL\u00b7E.[\/caption]\r\n\r\nNow we are able to determine other characteristics of the molecule including bonding angle, electron pair geometry, and molecular shape using the quick reference chart below.\r\n\r\nQuick reference chart\r\n

            \r\n
            \r\n
            \r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
            # of Domains<\/th>\r\n# of Lone Pairs<\/th>\r\nElectron Geometry<\/th>\r\nMolecular Shape<\/th>\r\nApproximate Bond Angles<\/th>\r\n<\/tr>\r\n<\/thead>\r\n
            1<\/td>\r\n0<\/td>\r\nLinear<\/td>\r\nLinear<\/td>\r\n180\u00b0<\/td>\r\n<\/tr>\r\n
            2<\/td>\r\n0<\/td>\r\nLinear<\/td>\r\nLinear<\/td>\r\n180\u00b0<\/td>\r\n<\/tr>\r\n
            3<\/td>\r\n0<\/td>\r\nTrigonal Planar<\/td>\r\nTrigonal Planar<\/td>\r\n120\u00b0<\/td>\r\n<\/tr>\r\n
            3<\/td>\r\n1<\/td>\r\nTrigonal Planar<\/td>\r\nBent<\/td>\r\n<120\u00b0<\/td>\r\n<\/tr>\r\n
            3<\/td>\r\n2<\/td>\r\nTrigonal Planar<\/td>\r\nLinear<\/td>\r\n<120\u00b0<\/td>\r\n<\/tr>\r\n
            4<\/td>\r\n0<\/td>\r\nTetrahedral<\/td>\r\nTetrahedral<\/td>\r\n109.5\u00b0<\/td>\r\n<\/tr>\r\n
            4<\/td>\r\n1<\/td>\r\nTetrahedral<\/td>\r\nTrigonal Pyramidal<\/td>\r\n<109.5\u00b0<\/td>\r\n<\/tr>\r\n
            4<\/td>\r\n2<\/td>\r\nTetrahedral<\/td>\r\nBent<\/td>\r\n<109.5\u00b0<\/td>\r\n<\/tr>\r\n
            4<\/td>\r\n3<\/td>\r\nTetrahedral<\/td>\r\nLinear<\/td>\r\n<109.5\u00b0<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n<\/div>\r\n<\/div>\r\n

            Using the quick reference chart above and the molecular structure of carbon dioxide, the molecular shape is linear with a 180\u00b0 bond angle.<\/p>\r\n\r\n<\/div>","rendered":"

            \n