Covalent bonds sigma bond

Alkanes, also called paraffins or aliphatic hydrocarbons, are hydrocarbons in which the C atoms are joined by single covalent bonds (sigma bonds) consisting of two shared electrons (see... 

In this section, we focus on the mode by which orbitals overlap—end to end or side to side—to see the detailed makeup of covalent bonds. These two modes give rise to the two types of covalent bonds—sigma bonds and pi bonds. WeTl use valence bond theory to describe the two types here, but they are essential features of molecular orbital theory as well. 

All flexible macromolecules must contain at least a sequence of linear, covalently bonded atoms. The understanding of the cylindrically symmetric, directed, covalent bonds (sigma bonds) was thus the first step towards polymer science. This step was already taken in 1858 by Kekuld as shown in Fig. 1.8. The detailed structures of large aggregates of atoms (macromolecules) could next be analyzed in detail after X-ray diffraction was fully understood. Major steps in the development of X-ray analysis of macromolecules are listed in the figure. First, rigid macromolecules such as metals, salts, minerals, and ceramics were analyzed. This was followed by many polymer crystal structures and even globular proteins. 

Alkanes, also called paraffins or aliphatic hydrocarbons, are hydrocarbons in which the C atoms are joined by single covalent bonds (sigma bonds) consisting of 2 shared electrons (see Section 4.5). Some examples of alkanes are shown in Figure 9.4. As with other organic compounds, the carbon atoms in alkanes may form straight chains, branched chains, or rings. These three kinds of alkanes are, respect-... 

A e-bond (sigma-bond) forms when the bonding pair of electrons are localized directly between the two bonding atonts. Since the electrons in a o-bond are as close as possible to the two sources of positive charge (the two nuclei), a o-boml has the lowest energy and is the most stable form of covalent bond. Thus o-bonds are strong. A o-bond is always the first type of covalent bond to be formed between any two atoms a single bond must be a c-bond. 

In alkanes or saturated hydrocarbons, each carbon atom forms four covalent bonds. These bonds are C —C and C — H sigma bonds. Sigma bonds are very strong, so for this reason, alkanes are also known as paraffins which means "inert". 

Figure 2.11. The sp hybrid orbital bonding (sigma bond) showing covalent bonding.

The two kinds of covalent bond are not identical, one being a simple covalent bond, a sigma (ct) bond, the other being a stronger (but more reactive) bond called a n bond (p. 56). As in the formation of methane both elements attain noble gas configurations. We can consider the formation of ethene as the linking of two tetrahedral carbon atoms to form the molecule C2H4 represented as ... 

A covalent bond is formed when an electron pair is shared between atoms. According to valence bond theory, electron sharing occurs by overlap of two atomic orbitals. According to molecular orbital (MO) theory, bonds result from the mathematical combination of atomic orbitals to give molecular orbitals, which belong to the entire molecule. Bonds that have a circular cross-section and are formed by head-on interaction are called sigma (cr) bonds bonds formed by sideways interaction ot p orbitals are called pi (77-) bonds. 

Sigma (covalent bond formed by head-on overlap of atomic orbitals. 

The polysilanes are compounds containing chains, rings, or three-dimensional structures of silicon atoms joined by covalent bonds. Recently, polysilane high polymers have become the subject of intense research in numerous laboratories. These polymers show many unusual properties, reflecting the easy delocalization of sigma electrons in the silicon-silicon bonds. In fact, the polysilanes exhibit behavior unlike that for any other known class of materials. 

The sigma phases are hard and brittle at below their Debye temperatures, but have some plasticity at higher temperatures. Thus there is some covalent bonding in them, and their glide planes are puckered, making it difficult for dislocations to move in them until they become partially disordered. Their structures are too complex to allow realistic hardness values to be calculated for them. Their shear moduli indicate their relative hardnesses. 

The symmetry properties of sigma orbital of a C-C-covalent bond is having a mirror plane symmetry and because a rotation of 180° through its mind point regenerates the same o orbital, it is also having C2 symmetry. The o orbital would be antisymmetric with respect to both m and C2 shown as follows ... 

In ethylene, there are two types of bonds. Sigma (tr) bonds have the overlap of the orbitals on a line between the two atoms involved in the covalent bond. In ethylene, the C-H bonds and one of the C-C bonds are sigma bonds. Pi (ir) bonds have the overlap of orbitals above and below a line through the two nuclei of the atoms involved in the bond. A double bond is always composed of one sigma and one pi bond. A carbon-to-carbon triple bond results from the... 

The formation of bonding molecular orbitals by an overlap of atomic orbitals applies not only to the Is orbitals of hydrogen, but also to other atomic orbitals. When the atomic orbitals overlap along the axis of the bond, a covalent bond, called a sigma (a) bond, results. This is normally referred to as end-on overlap. Some examples of the formation of a bonds from overlapping atomic orbitals are shown in the diagrams. 

Covalent bonds are formed when atomic orbitals overlap. The overlap of atomic orbitals is called hybridization, and the resulting atomic orbitals are called hybrid orbitals. There are two types of orbital overlap, which form sigma (cr) and pi (tt) bonds. Pi bonds never occur alone without the bonded atoms also being joined by a ct bond. Therefore, a double bond consists of a O bond and a tt bond, whereas a triple bond consists of a ct bond and two tt bonds. A sigma overlap occurs when there is one bonding interaction that results from the overlap of two s orbitals or an s orbital overlaps a p orbital or two p orbitals overlap head to head. A tt overlap occurs only when two bonding interactions result from the sideways overlap of two parallel p... 

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