Sticks representing bonds

Ball and stick model (Section 1 10) Type of molecular model in which balls representing atoms are connected by sticks representing bonds Similar to ball and spoke models of Learning By Modeling... 

Use the molecular-model building kit constructed in Activity 1.1 to make ball-and-stick models of the molecules listed on the chalkboard. The balls represent atoms and the sticks represent bonds. 

Balls represent atoms sticks represent bonds and lobes represent lone pairs of electrons. 260 Chapter 9 Covalent Bonding... 

The next most important aspect of a molecular compound is its shape. The pictorial representations of molecules that most accurately show their shapes are images based on computation or software that represents atoms by spheres of various sizes. An example is the space-filling model of an ethanol molecule shown in Fig. C.2a. The atoms are represented by colored spheres (they are not the actual colors of the atoms) that fit into one another. Another representation of the same molecule, called a ball-and-stick model, is shown in Fig. C.2b. Each ball represents the location of an atom, and the sticks represent the bonds. Although this kind of model does not represent the actual molecular shape as well as a space-filling model does, it shows bond lengths and angles more clearly. It is also easier to draw and interpret. 

In a ball-and-stick model, balls represent atoms, and sticks represent chemical bonds. The balls are labeled with elemental symbols or with different colors to distinguish among different elements. Figure includes ball-and-stick models, and Figure 3A shows a ball-and-stick model of propane. 

Chemists use a variation on the ball-and-stick model to depict more clearly the three-dimensional character of molecules, as shown for methane in Figure 9-1 Icf. The central carbon atom is placed in the plane of the paper, hi these models, solid lines represent bonds lying in the plane of the paper, solid wedges represent bonds that protmde outward from the plane of the paper, and dashed wedges represent bonds extending backward, behind the plane. 

Sticks and springs are used to represent bonds. Single bonds are shown with sticks, while double bonds are shown with two springs. A pair of dots ( ) or a dash (—) is used to represent a single bond in a drawn structure. A double bond is shown as two pair of dots ( ) or two dashes (=). 

Where the circle represents the two carbon and sticks the bonds. Now, if we allow the stick joining the two carbon nuclei to rotate freely in the holes, then an infinite number of different atomic arrangements becomes possible. 

All of these chemical species have importance in the production of polymeric materials. There are several shorthand techniques for writing down the structures of polymers. The carbon-based polymer molecules using the stick representation are made up of atoms connected by covalent bonds (represented here by the straight lines between the carbon and the hydrogen and the carbon-to-carbon molecules), as shown in Fig. 2.6. To reiterate, carbon is always tetravalent, having four covalent bonds, and a schematic of the paired electrons for two of the incorporated carbon molecules can be seen in the bottom of Fig. 2.6. Thus each stick represents two electrons. For the two highlighted carbon atoms in the polyethylene molecule of Fig. 2.6, the electron representation is shown, where there are four covalent bonds associated with each carbon and each bond is made up of two shared electrons represented by the black dots. This polymer molecule is made up of only carbon and hydrogen with no double bonds, and it represents a linear form... 

Ball-and-stick models of organic substances provide a convenient means of studying the structures of various organic compounds. Balls with holes represent the atoms, and sticks represent the covalent bonds. Figure 1-3 shows two conformations of ethane in which the dark balls represent carbon and the light balls represent hydrogen. All bond angles are the normal 109.5°. 

Figure 1 Important residues for delta receptor structure-activity. (A) Lateral view of a 3D model of the human delta opioid receptor. This model is based on x-ray crystallographic data from rhodopsin [91]. Helices are indicated as ribbons, side chains of amino acids implicated in binding (dark gray) or both binding and activation (light gray) are shown as sticks. Hydrophilic bonds are shown as dotted lines. (B) Position of important residues along the human delta opioid receptor sequence [34] using the same color code. (C) Scheme representing the receptor viewed from the extracellular face using the same color code.

Fig. 18. Redox-coupled conformational change in a loop between helices I and II of subunit I. A stereoview (A, see color insert) and a schematic representation of the hydrogen bond network connecting Asp-51 with the matrix space (B). (A) The molecular surface on the intermembrane side is shown by small dots. Maroon and green sticks represent the structures in the fully oxidized and reduced states. (B) Dotted lines show hydrogen bonds. The rectangle represents a cavity near heme a. The two dotted lines connecting the matrix surface and the cavity represent the water path. The dark balls show the positions of the fixed water molecules.

We will begin to represent molecules with models having balls for atoms and sticks for bonds, as in the ball-and-stick model of acetylene just shown. These representations are analogous to a set of molecular models. Balls are color-coded using accepted conventions carbon (black), hydrogen (white or gray), oxygen (red), and so forth. 

In this case, two-dimensional representations of starting material and product are more convenient than the spatial drawings for correlation analysis. Once this is done one can see that there are not one but at least four ways to move about the little. sticks representing C-C bonds to convert I into II (see Scheme 53.2). 

Ball-and-stick models. Ball-and-stick models are not as realistic as space-filling models, because the atoms are depicted as spheres of radii smaller than their van der Waals radii. However, the bonding arrangement is easier to see because the bonds are explicitly represented as sticks. In an illustration, the taper of a stick, representing parallax, tells which of a pair of bonded atoms is closer to the reader. A ball-and-stick model reveals a complex structure more clearly than a space-filling model does. 

The picture of molecules being composed of structural units, functional groups , which behave similarly in different molecules forms the very basis of organic chemistry. The drawing of molecular structures where alphabetic letters represent atoms and lines represent bonds is used universally. Organic chemists often build ball and stick, or CPK space-filling, models of their molecules to examine their shapes Force, field methods are... 

Figure 2-6 Formulas and models for some molecules. Structural formulas show the order in which atoms are connected but do not represent true molecular shapes. Ball-and-Stick models use balls of different colors to represent atoms and sticks to represent bonds they show the three-dimensional shapes of molecules. Space-fiUing models show the (approximate) relative sizes of atoms and the shapes of molecules.

In these ways the pictures used by chemists for nearly a century, in which covalent bonds are represented by sticks projecting from holes in the bonded atoms, are remarkably well justified. Like sticks, the bonds have determinable lengths. Like sticks, they project from the atoms at determinable angles. A single bond permits groups of atoms to rotate fairly freely about it, much as a stick would permit them. And atoms that are connected by several bonds are restrained from rotating about them, much as sticks would restrain them. 

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