Double bond Two pairs of electrons

Note In VSEPR theory the term bond pair is used for a single bond, a double bond, or a triple bond, even though a single bond consists of one pair of electrons, a double bond two pairs of electrons, and a triple bond three pairs of electrons. To avoid any confusion between the number of electron pairs actually involved in the bonding to a central atom, and the number of atoms bonded to that central atom, we shall occasionally use the term ligand" to indicate an atom or a group of atoms attached to the central atom. 

In addition, carbon atoms can form strong single, double, or triple bonds with other carbon atoms. In a single carbon-carbon bond, one pair of electrons is shared between two carbon atoms. In a double bond, two pairs of electrons are shared between two atoms. In a triple bond, three pairs of electrons are shared between two atoms. 

This pattern is typical in all reactions in which the reaction is catalyzed by an acid. Remember that in a carbon-carbon double bond, two pairs of electrons are shared between the two carbon atoms. An acid-base reaction in which a double bond provides the pair of electrons for the hydrogen transfer creates a carbocation. And remember that, as shown in Section 2.2, a proton, H, does not exist as such in aqueous solution. Instead it immediately combines with a water molecule to form the hydronium ion, H30. ... 

Every group of electrons shared between two atoms constitutes a covalent bond. When one pair of electrons is involved, the bond is called a single bond. When two pairs of electrons unite two atoms, the bond is called a double bond. Three pairs of electrons shared between two atoms constitute a triple bond. Examples of these types of bonds arc given below ... 

A double bond involves two pairs of electrons. In a double bond, one pair of electrons forms a single bond and the other pair forms an additional, weaker bond. The electrons in the additional, weaker bond react faster than the electrons in the single bond. Thus, carbon-carbon double bonds are more reactive than carbon-carbon single bonds. When an alkene reacts, the reaction almost always occurs at the site of the double bond. 

Whenever it is possible to draw two or more Lewis structures for a species that differ only in the location of a double bond between the same two kinds of atoms (N and O in this case), the true structure of the species is the average of the individual structures. In a sense, two of the four electrons in the double bond move from one N-O bond to the next so quickly that each bond is more than a single but not quite a double bond. That pair of electrons is not localized between two atoms rather it is delocalized over the entire species. Delocalization gives rise to a condition known as resonance, which adds stability to the species. One way delocalization can be shown in a Lewis structure is to use dotted lines to represent the pair of delocalized electrons, as shown in the following figure. This figure is a composite of the three resonance forms of the nitrate ion. 

Ethene (C2H4) is an example of a simple double-bonded carbon molecule, with two hydrogen atoms bonding to each carbon and the two carbons connected by a double bond. This is really only part of the answer. In a double covalent bond, two pairs of electrons are shared between two atoms instead of one pair. Figure 10.3 shows how the electrons are shared in ethene. 

In some cases, atoms attain a noble gas configuration by sharing more than one pair of electrons, forming a multiple covalent bond. In a double covalent bond, two pairs of electrons are shared. In a triple covalent bond, three pairs are shared. A multiple covalent bond always consists of a sigma bond and at least one pi bond, a bond in which parallel orbitals overlap. A pi bond occupies space above and below the line that represents where the two atoms are joined. 

In a double covalent bond, two pairs of electrons are shared between bonded atoms. The bond is represented by a double-dash sign (=). 

Bonded atoms can share more than one electron pair. A double bond occurs when bonded atoms share two electron pairs in a triple bond, three pairs of electrons are shared. In ethylene (Q2H4) and acetylene (QHJ, the carbon atoms are linked by a double bond and triple bond, respectively. Using two parallel lines to represent a double bond and three for a triple bond, we write the structures of these molecules as... 

In Section 7.2, we saw that insofar as geometry is concerned, a multiple bond acts as if it were a single bond. In other words, the extra electron pairs in a double or triple bond have no effect on the geometry of the molecule. This behavior is related to hybridization. The extra electron pairs in a multiple bond (one pair in a double bond, two pairs in a triple bond) are not located in hybrid orbitals. 

In the structural formula for O2, the sharing of two pairs of electrons is represented by two parallel dashes—a double bond. Sometimes three pairs of electrons are shared, producing a triple bond, which is indicated by three parallel dashes. 

Double bond A covalent bond in which two pairs of electrons are shared. 

Double bonds, representing the sharing of two pairs of electrons, are inferred by writing a double line. Vinyl chloride (systematically chloroethene) is shown as two different representations according to the conventions we have just seen for propanol. Note that it is customary always to show the reactive double bond, so that CH2CHCI would not be encountered as an abbreviation for vinyl chloride. 

The structure of Cgp consists of carbon atoms bonded together in the shape of a soccer ball. In the figure, the dots [or nodes] represent carbon atoms, and the lines represent bonds, some of which are double bonds in which two pairs of electrons are shared. 

Atoms can share more than a single pair of electrons. When atoms share two pairs of electrons, they re said to form a double bond, and when they share three pairs of electrons, they re said to form a triple bond. Figure 5-5 shows examples of double and triple bonds using electron dot structures and line structures. 

Double bond A bond formed by the sharing of two pairs of electrons between two atoms. 

Elements in organic compounds are joined by covalent bonds, a sharing of electrons, and each element contributes one electron to the bond. The number of electrons necessary to complete the octet determines the number of electrons that must be contributed and shared by a different element in a bond. This analysis finally determines the number of bonds that each element may enter into with other elements. In a single bond two atoms share one parr of electrons and form a a bond. In a double bond they share two pairs of electrons and form a a bond and a tt bond. In a triple bond two atoms share three parrs of electrons and form a cr bond and two tt bonds. 

Each oxygen needs to share two electrons to gain the electron configuration of neon. This is achieved by forming two double covalent bonds in which two pairs of electrons are shared in each case, as shown in Figure 3.28. Carbon dioxide is a linear molecule (Figure 3.29). 

Once the theory of pericyclic reactions was developed, it was recognized that the conversion of Dewar benzene to benzene is an electrocyclic reaction. This conversion involves two pairs of electrons one pair of pi electrons and one pair of sigma electrons of the Dewar benzene. (The third pair of electrons is located in exactly the same place in both the reactant and the product and so is not involved in the reaction.) An electrocyclic reaction involving two pairs of electrons must occur by a conrotatory motion if it is to be thermally allowed. However, the conrotatory opening of Dewar benzene is geometrically impossible, because it would result in a benzene with a trans double bond, a compound with too much angle strain to exist. 

This is shown most commonly with two joining lines, 0=0. This represents a double bond with two pairs of electrons. The bonds are formed only by the outer or valence electrons. 

In a Lewis structure, the double bond of an alkene is represented by two pairs of electrons between the carbon atoms. The Pauli exclusion principle tells us that two pairs of electrons can go into the region of space between the carbon nuclei only if each pair has its own molecular orbital. Using ethylene as an example, let s consider how the electrons are distributed in the double bond. 

Ethylene (C2H4) is an organic compound with a double bond. When we draw a Lewis structure for ethylene, the only way to show both carbon atoms with octets is to draw them sharing two pairs of electrons. The following examples show organic compounds with double bonds. In each case, two atoms share four electrons (two pairs) to give them octets. A double dash (=) symbolizes a double bond. 

Shared pairs of electrons (one electron from each atom) are usually shown as a simple straight line, so methane is drawn as shown in Figure 2.3. There is no such thing as this stick-like formation, but it is a convenient way of representing a pair of electrons between atoms, one from each atom. Now look at another familiar compound - carbon dioxide (Figure 2.4). We write carbon dioxide in its abbreviated form as 0=C=0 or C02. There are two pairs of electrons between each carbon and oxygen atom. We call this a double bond. 

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