Chlorine covalent bonds

In the presence of chloride ion, metal electrodes facilitate its oxidation [Eq. (75) E°, 4-2.41 V vs NHE] via formation of metal-chlorine covalent bonds, e.g.,... 

Bonds may also be broken symmetrically such that each atom retains one electron of the pair that formed the covalent bond. This odd electron is not paired like all the other electrons of the atom, i.e. it does not have a partner of opposite spin. Atoms possessing odd unpaired electrons are termed free radicals and are indicated by a dot alongside the atomic or molecular structure. The chlorination of methane (see later) to produce methyl chloride (CH3CI) is a typical free-radical reaction ... 

Chemists refer to the bond in a molecule like sodium chloride as ionic , meaning that its electron pair resides entirely on chlorine. At the other extreme is the covalent bond in the hydrogen molecule, where the electron pair is shared equally between the two hydrogens. Intermediate cases, such as the bond in hydrogen fluoride which is clearly polarized toward fluorine, are generally referred to as polar covalent bonds (rather than partially ionic bonds). Are these situations really all different or do they instead represent different degrees of the same thing ... 

The electronic structure of the chlorine atom (3s-3p ) provides a satisfactory explanation of the elemental form of this substance also. The single half-filled 3p orbital can be used to form one covalent bond, and therefore chlorine exists as a diatomic molecule. Finally, in the argon atom all valence orbitals of low energy are occupied by electrons, and the possibility for chemical bonding between the atoms is lost. 

Elements that can expand their valence shells commonly show variable covalence, the ability to form different numbers of covalent bonds. Elements that have variable covalence can form one number of bonds in some compounds and a different number in others. Phosphorus is an example. It reacts directly with a limited supply of chlorine to form the toxic, colorless liquid phosphorus trichloride ... 

The difference in electronegativity between sodium and chlorine and between hydrogen and oxygen causes one pair of atoms to form an ionic bond and the other pair to form a covalent bond. 

The electronegativity of sodium and chlorine differ by 2.23, whereas the difference between hydrogen and oxygen is only 1.24 (see Table 7.1). As a general rule, molecules made up of two atoms with electronegativity differences greater than 2.0 form ionic bonds. Molecules whose atoms have electronegativity differences of less than 2.0 form covalent bonds. Ionic-bonded salt and covalent-bonded water conform to that rule. 

Because of the electric interaction, hydrogen-bonded molecules hold on to each other more tightly than those in substances with pure covalent bonds. This cohesiveness is why water is a liquid at room temperature, whereas heavier covalent-bonded molecules such as chlorine, in the form of CI2, are gases. 

Chlorine is much more electronegative than carbon, so a strong electric dipole exists between each chlorine and the carbon atom. The chlorine atoms are symmetrically arranged around the carbon so that the molecule itself is not polar, even though it has four polar covalent bonds between its atoms. 

Because chlorine is more electronegative than carbon, carbon tetrachloride has four polar covalent bonds. But, as pointed out earlier, the molecular symmetry cancels out the electric dipoles of the individual bonds. The result is a nonpolar molecule. Like water, carbon tetrachloride is a good solvent. At one time, it was used as a dry cleaning agent. Water and carbon tetrachloride, however, dissolve entirely different classes of compounds. Carbon tetrachloride forms solutions with nonpolar organic compounds. It is infinitely miscible, for example, with benzene, whereas water and benzene do not mix. 

The acyl-enzyme can eliminate the 4-chlorine atom to generate this reactive intermediate that can then react with a nearby nucleophile such as His57 to give an alkylated acyl-enzyme derivative in which the inhibitor moiety is bound to the enzyme by two covalent bonds (Scheme 11.5). Inhibition is irreversible.59 The mechanism has been confirmed by X-ray structural analysis of protease-isocoumarin complexes. There is a cross-link between the inhibitor and the Serl95 and His57 residues of PPE.60 Human leukocyte elastase is also very efficiently inactivated.61... 

The kind of bond between neighboring atoms also has to be considered. For instance, the coordination number for a chlorine atom in the CC14 molecule is 1 when only the covalently bonded C atom is counted, but it is 4 (1 C + 3 Cl) when all atoms in contact are counted. In the case of molecules one will tend to count only covalently bonded atoms as coordinated atoms. In the case of crystals consisting of monoatomic ions usually only the anions immediately adjacent to a cation and the cations immediately adjacent to an anion are considered, even when there are contacts between anions and anions or between cations and cations. In this way, an I- ion in Lil (NaCl type) is assigned the coordination number 6, whereas it is 18 when the 12 I- ions with which it is also in contact are included. In case of doubt, one should always specify exactly what is to be included in the coordination sphere. 

The first represents a hypothetical HC1 molecule with a purely covalent bond in which the two bonding electrons are equally shared between the two atoms, and the second a hypothetical molecule with a purely ionic bond in which both the bonding electrons have been transferred to the chlorine atom. In this case the two resonance structures do not necessarily... 

Am. (a) The chlorine atoms are bonded to each other with a covalent bond. (h) The chlorine atoms are both bonded to the sulfur atom with covalent bonds, (r) The chlorine atoms are changed to Cl ions, and are bonded to the magnesium ion by ionic bonds. 

Oxyanions consist of an atom of an element plus some number of atoms of oxygen covalently bonded to it. The name of the anion is given by the name of the element with its ending changed to either -ate or -ite. In some cases, it is also necessary to add the prefix per- or hypo- to distinguish all the possible oxyanions from one another. For example, there are four oxyanions of chlorine, which are named as follows ... 

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