Hydrogen polyatomic ions

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). 

C09-0107. Write Lewis structures and calculate formal charges for the following polyatomic ions (a) bromate (b) nitrite (c) phosphate and (d) hydrogen carbonate. 

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

Not all bases contain hydroxide, however. For example, Na2C03 is a base, but its name is sodium carbonate. Baking soda, which has a chemical formula of NaHC03, is also a base. The scientific name for baking soda is sodium hydrogen carbonate (hydrogen carbonate is the name of the 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. 

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). 

Binary acids You can easily recognize a binary acid when you see hydrogen bonded to a nonmetallic element or polyatomic ion without oxygen present. 

J 1 Oxy-acids Oxy-acids contain hydrogen bonded to a polyatomic ion containing oxygen. To name a binary acid (no oxygen), use the following steps ... 

An atom in a polyatomic ion or in a molecular compound usually has the same oxidation number it would have if it were a monatomic ion. In the hydroxide ion (OH-), for example, the oxygen atom has an oxidation number of -2, as if it were a monatomic O2- ion, and the hydrogen atom has an oxidation number of +1, as if it were H+. 

An oxoacid is an acid formed from a polyatomic ion that contains oxygen, hydrogen, and another element. (Oxoacids are called oxyacids in some chemistry textbooks). In Chapter 3, you learned the names of common polyatomic ions and their valences (oxidation numbers). The names of oxoacids are similar to the names of their polyatomic oxoanions. Only the suffix is different. Study the three rules and examples for naming oxoacids below. Then try the Practice Problems that follow. 

Formal charge can also help answer the question where is the charge located that is frequently asked about polyatomic ions. Thus by writing out the Lewis structure for the ammonium ion NH4+, you should be able to convince yourself that the nitrogen atom has a formal charge of +1 and each of the hydrogens has 0, so we can say that the positive charge is localized on the central atom. 

What polyatomic ion does the hydrogen ion, H, form in aqueous solution ... 

Although the term binary indicates exactly two elements, a few acids that contain more than two elements are named according to the rules for naming binary acids. If no oxygen is present in the formula for the acidic compound, the acid is named in the same way as a binary acid, except that the root of the second part of the name is the root of the polyatomic ion that the acid contains. For example, HCN, which is composed of hydrogen and the cyanide ion, is called hydrocyanic acid. 

Naming oxyacids Another set of rules is used to name an acid that contains an oxyanion. An oxyanion is a polyatomic ion that contains oxygen. Any acid that contains hydrogen and an oxyanion is referred to as an oxyacid. 

Step 2 Count the atoms of the elements in the reactants. If a reaction involves identical polyatomic ions in the reactants and products, count the ions as if they are elements. This reaction does not involve any polyatomic ions. Two atoms of hydrogen and two atoms of chlorine are reacting. 

What does it mean to be a hydrogen-ion donor or a hydrogen-ion acceptor The symbols X and Y may be used to represent nonmetallic elements or negative polyatomic ions. Thus the general formula for an acid can be written as HX or HY. When a molecule of acid, HX, dissolves in water, it donates a H+ ion to a water molecule. The water molecule acts as a base and accepts the H+ ion. 

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