Compounds Sharing Electrons

A molecular compound contains two or more nonmetals that form covalent bonds. Because nonmetals have high ionization energies, valence electrons are shared by non-metal atoms to achieve stability. When atoms share electrons, the bond is a covalent bond. When two or more atoms share electrons, they form a molecule. 

The simplest molecule is hydrogen, H2. When two H atoms are far apart, there is no attraction between them. As the H atoms move closer, the positive charge of each nucleus attracts the electron of the other atom. This attraction, which is greater than the repulsion between the valence electrons, pulls the H atoms closer until they share a pair of valence electrons (see Fignre 6.5). The result is called a covalent bond, in which the shared electrons give the noble gas arrangement of He to each of the H atoms. When the H atoms form H2, they are more stable than two individual H atoms. 

FIGURE 6.5 A covalent bond forms as H atoms move close together to share electrons. 

The elements hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine exist as diatomic molecules. 

The valence electrons in molecules are shown using an electron-dot formula, also called a Lewis structure. The shared electrons, or bonding pairs, are shown as two dots or a single line between atoms. The nonbonding pairs of electrons, or lone pairs, are placed on the outside. For example, a fluorine molecule, F2, consists of two fluorine atoms, which are in Group 7A (17), each with seven valence 

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Aromatics Unsaturated hydrocarbons such as benzene, toluene, xylene, and related compounds. Aromatic compounds share electrons equally among carbon atoms. 

Atoms often bond to one another to form a compound. These bonds can involve the sharing of valence electrons. Not all atoms in a compound share electrons equally. Knowing how strongly each atom attracts bonding electrons can help explain the physical and chemical properties of the compound. 

The atoms in these other compounds share electrons. The chemical bond that results from the sharing of valence electrons is a covalent bond. In a covalent bond, the shared electrons are considered to be part of the complete outer energy level of both atoms involved. Covalent bonding generally occurs when elements are relatively close to each other on the periodic table. The majority of covalent bonds form between nonmetallic elements. 

But many other compounds exist in which electron transfer hasn t occurred. The driving force is still the same achieving a filled valence energy level. But instead of achieving it by gaining or losing electrons, the atoms in these compounds share electrons. That s the basis of a covalent bond. 

Chapter 6, Ionic and Molecular Compounds, describes the formation of ionic and covalent bonds. Chemical formulas are written, and ionic compounds—including those with polyatomic ions—and molecular compounds are named. Section 6.1 is now titled Ions Transfer of Electrons, 6.2 is titled Writing Formulas for Ionic Compounds, 6.3 is titled Naming Ionic Compounds, and 6.5 is titled Molecular Compounds Sharing Electrons. ... 

Octet rule (Section 1 3) When forming compounds atoms gain lose or share electrons so that the number of their va lence electrons is the same as that of the nearest noble gas For the elements carbon nitrogen oxygen and the halo gens this number is 8... 

The third main type of bond is the co-ordinate bond, in which both of the shared electrons come from one atom. Examples of interest in polymer science are the addition compounds of boron trifluoride Figure 5.3). 

In the early part of the twentieth century, G. N. Lewis observed that chemical bonding seemed to favor a state in which the atoms in stable compounds, by sharing electrons, achieved the stable electron distribution exhibited by the nonreactive noble gases, so-called because they are almost always found as pure elements in the gas state. He proposed that the electrons shared between two elements act as an electromagnetic glue to hold the two atoms together. The positive nuclei are attracted to the negative electrons the electrons spend most of their... 

A nonionic compound is made up of covalent bonds only. A covalent bond results from shared electron pairs between two atoms. It consists of electrostatic attraction between each electron and both nuclei, e.g.. 

Compounds of septivalent chlorine probably contain chlorine with a polar valence of +3 and with four shared electron bonds. Thus the perchlorate ion would be formed from Cl +3 and 4 0 and would have... 

In a covalent compound of known structure, the oxidation number of each atom is the charge remaining on the atom when each shared electron pair is assigned completely to the more electronegative of the two atoms sharing it. A pair shared by two atoms of the same element is split between them. 

Throughout our discussion the crystals will be referred to as composed of ions. This does not signify that the chemical bonds in the crystal are necessarily ionic in the sense of the quantum mechanics they should not, however, be of the extreme non-polar or shared electron pair type.13 Thus compounds of copper14 and many other eighteen-shell atoms cannot be... 

Each line in a structural formula represents one pair of shared electrons, but atoms can share more than one pair of electrons. When two atoms share one pair of electrons, the bond is called a single bond, and the structural formula shows a single line. When two atoms share four electrons, the bond is called a double bond, and the structural formula shows two lines between the atoms. Similarly, when two atoms share six electrons, the bond is called a triple bond, and the stmctural formula shows three lines between the atoms. Two carbon atoms can bond to each other through any of these three kinds of bonds, as the compounds in Figure illustrate. 

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