7 - Chapter 7 Molecules as objects representing molecular...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Chapter 7 – Molecules as objects: representing molecular structure with models Molecules are a collection of point masses of fixed positive charge; this positive charge creates a field of force that binds the negatively charged electrons. More than 99.9% of the atom’s mass is contained in the nucleus yet the diameter of the nucleus is 10,000 times smaller than the diameter of the space occupied by the electrons. In other words, the vast majority of space assigned to a molecule is virtually empty, occupied only by the tiny mass of the electrons. When describing geometric aspects of molecular structure, we need to know the position of the atoms. The Cartesian x , y , and z coordinates of an atom’s nucleus provide a useful means of pinpointing its location in space since the majority of the atom’s mass can be found there. This ability to quantitatively describe the position of an atom using nuclear coordinates gives precise meaning to van’t Hoff and le Bell’s notion 1 of molecular geometry – the idea that atoms occupy a definite arrangement in three dimensional space, thereby serving as attachment points for structural connections. Organic molecules are three-dimensional (3D) objects, not the 2D line-angle drawings that we write on a piece of paper. The ability to interpret line-angle drawings as 3D objects is a learned skill. Just like any other skill, you will need to practice if you expect to become proficient at the task. To facilitate the development of this skill, students must take an active role in the learning process, by using physical models (i.e., plastic molecular model kits) and / or software that aid 3D visualization. These visualization aids will help you understand the relationship between a molecule's three dimensional structure and its two dimensional projection. Instructions for using your molecular model kit Your molecular modeling kit contains spheres that represent the hydrogen atoms, colored polyhedra that represent the non-hydrogen atoms, cylindrical pegs that represent bonds, and balloon-shaped sheets that represent orbitals. The polyhedra display a series of holes intended to accommodate a varied combination of bonds at angles that mimic atomic geometries. Make sure you use the holes that are angled at the desired geometries for organic chemistry (180 ˚ for linear; 120 ˚ for planar; 109 ˚ for tetrahedral). The cylindrical pegs you choose for bonds should be of the same length. A detailed set of instructions and information regarding interpretation of scale is available online: http://www.hgs-model.com/manual/1000/1000.html 3D Visualization with computer software MarvinSketch is an advanced, Java-based chemical editor for drawing chemical structures, queries and reactions. It has many editing features and is “chemically aware,” meaning that it warns the user of possible drawing errors. The software is free and plugs into nearly all available modern web browsers. You can find MarvinSketch at the URL listed below: ( http://www.chemaxon.com/demosite/marvin/index.html ).
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern