Bonding polyatomic ions

The compounds described in Example 10-2 are binaty ionic compounds consisting of monatomic cations and monatomic anions. Commonly encountered ternary ionic compounds consist of monatomic and polyatomic ions. Bonding between atoms within the polyatomic ions is covalent. Some ternary ionic compounds are considered later in the chapter. 

The ions dealt with to this point (e.g., Na+, Cl-) are monatomic that is, they are derived from a single atom by the loss or gain of electrons. Many of the most important ions in chemistry are polyatomic, containing more than one atom. Examples include the hydroxide ion (OH-) and the ammonium ion (NH ). In these and other polyatomic ions, the atoms are held together by covalent bonds, for example,... 

The concept of oxidation number is used to simplify the electron bookkeeping in redox reactions. For a monatomic ion (e.g., Na+, S2 ), the oxidation number is, quite simply, the charge of the ion (+1, —2). In a molecule or polyatomic ion, the oxidation number of an element is a pseudo-charge obtained in a rather arbitrary way, assigning bonding electrons to the atom with the greater attraction for electrons. 

This chapter is devoted to the covalent bond as it exists in molecules and polyatomic ions. We consider—... 

These examples illustrate the principle that atoms in covalently bonded species tend to have noble-gas electronic structures. This generalization is often referred to as the octet rule. Nonmetals, except for hydrogen, achieve a noble-gas structure by sharing in an octet of electrons (eight). Hydrogen atoms, in molecules or polyatomic ions, are surrounded by a duet of electrons (two). 

One form of the polyatomic ion I, has an unusual V-shaped structure one I atom lies at the point of the V, with a linear chain of two I atoms extending on each side. The bond angles are 88° at the central atom and 180° at the two atoms in the side chains. Draw a Lewis structure for L that explains its shape and indicate the hybridization you would assign to each nonterminal atom. 

In the polyatomic ion the formation of a coordinate covalent bond between nitrogen and hydrogen involves —... 

Distinguish between each of the following pairs (a) an ion and an ionic bond, (b) an ion and a free atom, (c) a covalent bond and an ionic bond, (cl) a triple bond and three single bonds on the same atom, (e) a polyatomic molecule and a polyatomic ion. 

The constituent atoms in polyatomic ions are also linked by covalent bonds. In these cases, the net charge on the ion is determined by the total number of electrons and the total number of protons. For example, the ammonium ion, NH4 +, formed from five atoms, contains one fewer electron than the number of protons. A nitrogen atom plus 4 hydrogen atoms contains a total of 11 protons and 11 electrons, but the ion has only 10 electrons, 8 of which are valence electrons. 

Polyatomic ions, such as OH , NO,, and NH4 + possess covalent bonds as well as an overall charge. 

The charges on polyatomic ions cause ionic bonding between these groups of atoms and oppositely charged ions. In writing electron dot structures, the distinction between ionic and covalent bonds must be clearly indicated. For example, an electron dot diagram for the compound NH4NO, would be... 

Ionic bonding results from electrostatic interactions between ions, which can be formed by the transfer of one or more electrons from a metal to a nonmetal or group of nonmetals (forming a polyatomic ion, like N03 ). Covalent bonding, on the other hand, results from sharing one or more electron pairs between two nonmetal atoms. 

NH4)2S04 is an ionic solid composed of covalently bonded polyatomic ions both obey the octet rule ... 

A molecule or polyatomic ion for which two or more Lewis formulas with the same arrangements of atoms can be drawn to describe the bonding is said to exhibit resonance. The two structures given here do not have the same arrangement of atoms, and hence are not resonance structures. 

This polyatomic ion (type AB6), like (c), does not obey the octet rule without modification since 12 electrons must be shared to form 6 Sb-F bonds. Sb is a 5 A element, but the charge on the ion gives an extra electron which participates in bonding. The Lewis formula predicts 6 electron groups around the central Sb atom and an octahedral electronic geometry. There are no lone pairs on the Sb atom, so the ionic geometry is the same as the electronic geometry (Section 8-12). 

Force Within Unit (Intra) covalent bond within polyatomic ion — — covalent bond... 

Some ionic compounds contain a combination of bonds. For instance, in polyatomic ions such as ammonium (NH4+), the hydrogen atoms are bonded to the nitrogen atom by polar covalent bonds. The ionic bond is thus between this covalently bonded moiety and another oppositely charged ion such as chloride (CT). 

In Sections 9-3 and 9-4, we will show you two types of chemical bonds ionic and covalent. It is important to be able to represent compounds in terms of the atoms and valence electrons that make up the chemical species (compounds or polyatomic ions). One of the best ways is to use Lewis symbols and structures. 

Ionic bonding is present in compounds containing a metal and a nonmetal or in a compound containing one or more polyatomic ions. There are a few exceptions to this generalization, but these usually do not appear in this type of question. An ionic substance must contain at least two different elements, so we... 

Ionic bonding may also involve polyatomic ions. The polyatomic ion(s) simply replace(s) one or both of the monoatomic ions. 

Ionic bonds can also result from the interaction of polyatomic ions. 

You know that a covalent bond involves the sharing of a pair of electrons between two atoms each atom contributes one electron to the shared pair. In some cases, such as the hydronium ion, HsO", one atom contributes both of the electrons to the shared pair. The bond in these cases is called a co-ordinate covalent bond. In terms of the quantum mechanical model, a co-ordinate covalent bond forms when a filled atomic orbital overlaps with an empty atomic orbital. Once a co-ordinate bond is formed, it behaves in the same way as any other single covalent bond. The next Sample Problem involves a polyatomic ion with a co-ordinate covalent bond. 

This polyatomic ion has six bonds around the central Si atom, an obvious exception to the octet rule, so the central atom needs an expanded valence shell. 

Oxidation numbers are just a bookkeeping method used to keep track of electron transfers. In a covalent molecule or a polyatomic ion, the oxidation number of each element does not represent an ionic charge, because the elements are not present as ions. However, to assign oxidation numbers to the elements in a covalent molecule or polyatomic ion, you can pretendthe bonds are ionic. 

Force within units Covalent bond within polyatomic ion Atomic forces between subatomic particles Atomic forces between subatomic particles Covalent bond... 

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