Ethyne Lewis structure

A single shared pair of electrons is called a single bond. Two electron pairs shared between two atoms constitute a double bond, and three shared electron pairs constitute a triple bond. A double bond, such as C 0, is written C=0 in a Lewis structure. Similarly, a triple bond, such as C C, is written G C. Double and triple bonds are collectively called multiple bonds. The bond order is the number of bonds that link a specific pair of atoms. The bond order in H, is 1 in the group C=0, it is 2 and, for O C in a molecule such as ethyne, C2H2, the bond order is 3. 

Now consider the alkynes, hydrocarbons with carbon-carbon triple bonds. The Lewis structure of the linear molecule ethyne (acetylene) is H—O C- H. To describe the bonding in a linear molecule, we need a hybridization scheme that produces two equivalent orbitals at 180° from each other this is sp hybridization. Each C atom has one electron in each of its two sp hybrid orbitals and one electron in each of its two perpendicular unhybridized 2p-orbitals (43). The electrons in the sp hybrid orbitals on the two carbon atoms pair and form a carbon—carbon tr-bond. The electrons in the remaining sp hybrid orbitals pair with hydrogen Ls-elec-trons to form two carbon—hydrogen o-bonds. The electrons in the two perpendicular sets of 2/z-orbitals pair with a side-by-side overlap, forming two ir-honds at 90° to each other. As in the N2 molecule, the electron density in the o-bonds forms a cylinder about the C—C bond axis. The resulting bonding pattern is shown in Fig. 3.23. 

Acetylene (ethyne), C2H2, can be polymerized, (a) Draw the Lewis structure for acetylene and draw a Lewis structure for the polymer that results when acetylene is polymerized. The polymer has formula (CH), where n is large, (b) Consider the polymers polyacetylene and polyethylene. The latter has the formula (CH2)W and is an insulating material (plastic wrap is made of polyethylene), whereas polyacetylene is a darkly colored material that can conduct electricity when properly treated. On the basis of your answer to part (a), suggest an explanation for the difference in the two polymers. 

Bond paths are observed between bonded atoms in a molecule and only between these atoms. They are usually consistent with the bonds as defined by the Lewis structure and by experiment. There are, however, differences. There is only a single bond path between atoms that are multiply bonded in a Lewis structure because the electron density is always a maximum along the internuclear axis even in a Lewis multiple bond. The value of pb does, however, increase with increasing Lewis bond order, as is shown by the values for ethane (0.249 au), ethene (0.356 au), and ethyne (0.427 au), which indicate, as expected, an increasing amount of electron density in the bonding region. 

A simple compound with a triple bond is ethyne (acetylene), HC=CH. The Lewis structure for ethyne is shown in Figure 3.14a. It is a linear molecule. One of the CC bonds is a sigma bond. The other two are pi bonds. 

Draw the Lewis structures for ethyne, C2H2, and hydrogen cyanide, HCN. 

This completes the Lewis structure of ethyne C2H2 with a triple bond. In C2H2 both C atoms have complete octets involving four shared electron pairs, one with the H atom and three with the second C atom. Each H atom has a single shared electron pair. 

Another molecule whose bonding can be described by sp hybridization is acetylene (C2FI2), which has the systematic name ethyne. The Lewis structure for acetylene is... 

How do the calculated bond orders for ethane, ethene, and ethyne compare to bond orders predicted by the Lewis structures ... 

Lewis formulas would place two electrons between the carbon atoms in ethane, four between the carbon atoms in ethene, and six electrons between the carbon atoms in ethyne. These Lewis structures are, of course, consistent with Lewis suggestion that two atoms joined by a double bond share four electrons, while two triply bonded atoms share six electrons. 

Lewis structures for (a) methane, (b) ethylene, and (c) ethyne, where the electrons are positioned at the corners of a tetrahedron for each carbon atom. 

FIGURE 1.21 Construction of a Lewis structure for ethyne (acetylene). 

Describe the bonding in ethyne (acetylene), C2H2, which has the Lewis dot structure ... 

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