Sharing Electrons with Covalent Bonds

Just as ionic bonds tend to form in such a way that both atoms end up with completely filled valence shells, the atoms involved in covalent bonds tend to share electrons in such a way that each ends up with a completely filled valence shell. The shared electrons are attracted to the nuclei of both atoms, forming the bond. 

Three representations of the formation of a covalent bond in a dihydrogen molecule. 

The valence electrons are the ones you can use to build the structure. Account for any extra or missing electrons in the case of ions. For example, if you know your molecule has a -1-2 charge, remember to subtract 2 from the total number of valence electrons. If your molecule has a -2 charge, remember to add 2 to the total valence number. 

In the case of formaldehyde, C has four valence electrons, each H has one valence electron, and 0 has six valence electrons. The total number of valence electrons is 12. 

Pick a central atom to serve as the anchor of your Lewis structure. 

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Delocalization (Section 1 9) Association of an electron with more than one atom The simplest example is the shared electron pair (covalent) bond Delocalization is important in conjugated tt electron systems where an electron may be associated with several carbon atoms... 

In other situations, the neutral oxygen atom may share electrons with one or more other atoms, in order to act as though it has a complete valence shell part of the time. These shared electrons represent covalent bonds and result in the formation of molecular compounds, as shown here ... 

Elements near the center of the p block have fewer p electrons and do not usually fill the p orbitals by forming anions instead they share electrons, forming covalent bonds. We see this type of reactivity in the vast array of molecular compounds formed by the smaller elements in the carbon and nitrogen groups. The main-group elements on the far left of the p block have only one p electron and form cations in ionic compounds and electron-deficient species (species with an incomplete octet) in covalent compounds. 

The complex cyanides of transition metals, especially the iron group, are very stable in aqueous solution. Their high co-ordination numbers mean the metal core of the complex is effectively shielded, and the metal-cyanide bonds, which share electrons with unfilled inner orbitals of the metal, may have a much more covalent character. Single electron transfer to the ferri-cyanide ion as a whole is easy (reducing it to ferrocyanide, with no alteration of co-ordination), but further reduction does not occur. 

The sodium and calcium salts of EDTA (ethylenediaminetetraacetic acid, Fig. 9.3.1.) are common sequestrants in food products. A three-dimensional representation of EDTA is shown in color Fig. 9.3.2. The EDTA ion is an especially effective sequestrant, forming up to six coordinate covalent bonds with a metal ion. These bonds are so named because a lone pair of electrons on a single atom serves as the source of the shared electrons in the bond between the metal ion and EDTA. The two nitrogen atoms in the amino groups and the oxygen... 

Oxygen has many uses because of its ability to accept electrons from other elements to form ionic bonds or to share electrons with other elements to form covalent bonds. 

The sharing of electrons between two atoms is called a covalent bond. Such bonds owe their stability to the interaction of the shared electrons with both positive nuclei. The nuclei will be separated by a certain distance — termed the bond distance -that maximizes the nuclear-electron attractions balanced against the nuclear-nuclear repulsion. A molecule is a neutral species of two or more atoms held together by covalent bonds. 

Customarily, carbon completes its valence-shell octet by sharing electrons with other atoms. In compounds with shared electron bonds (or covalent bonds) such as methane, ethane, or tetrafluoromethane, each of the bonded atoms including carbon has its valence shell filled, as shown in the following electron-pair or Lewis6 structures ... 

A covalent bond occurs when two atoms, both in need of electrons to become stable, share electrons that are usually from their outermost energy shells. Instead of one atom giving an electron to another atom, the atoms overlap and share electrons still bound to its nucleus. When a solid formed with covalent bonds melts or freezes, the strength of the covalent bonds that form the molecules are overcome by the strength of the intermolecular forces. 

Hybrid orbitals can hold up to two electrons half-filled hybrid orbitals can share electrons with other half-filled orbitals to form a covalent bond. 

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