What is an inorganic acid which is composed of two elements hydrogen and a nonmetal?

Adapted from McMurry/Fay, section 2.10, p. 56-63
and the 1411 Lab Manual, p. 27-31. (References)

Contents:
Types of Compounds
Types of Ions:
     Main-Group Metals (Groups IA, IIA, and IIIA)
     Transition (B-group) and Post-Transition (Group IVA and VA) Metals
     Main-Group Nonmetals (Groups IVA, VA, VIA, and VIIA)
     Polyatomic Ions
Writing Formulas of Ionic Compounds
Nomenclature of Ionic and Covalent Compounds
     1.  Binary Ionic Compounds Containing a Metal and a Nonmetal
     2.  Ionic Compounds Containing a Metal and a Polyatomic Ion
     3.  Acids and Acid Salts
     4.  Binary Covalent Compounds Between Two Nonmetals
     5.  Hydrocarbons
Molecular Masses from Chemical Formulas
References

Types of Compounds

Ionic compounds are compounds composed of ions, charged particles that form when an atom (or group of atoms, in the case of polyatomic ions) gains or loses electrons.

• A cation is a positively charged ion
• An anion is a negatively charged ion.

Covalent or molecular compounds form when elements share electrons in a covalent bond to form molecules. Molecular compounds are electrically neutral.

Ionic compounds are (usually) formed when a metal reacts with a nonmetal (or a polyatomic ion).  Covalent compounds are formed when two nonmetals react with each other.  Since hydrogen is a nonmetal, binary compounds containing hydrogen are also usually covalent compounds.

• Metal  +  Nonmetal  —>  ionic compound (usually)
• Metal  +  Polyatomic ion  —>  ionic compound (usually)
• Nonmetal  +  Nonmetal  —>  covalent compound (usually)
• Hydrogen  +  Nonmetal  —>  covalent compound (usually)

Types of Ions:

Main-Group Metals (Groups IA, IIA, and IIIA)

Group IA, IIA, and IIIA metals tend to form cations by losing all of their outermost (valence) electrons. The charge on the cation is the same as the group number. The cation is given the same name as the neutral metal atom.

Ions of Some Main-Group Metals (Groups IA - IIIA)

Transition (B-group) and Post-Transition (Group IVA and VA) Metals

These elements usually form ionic compounds; many of them can form more than one cation. (The charges of the common transition metals must be memorized; Group IV and V metal cations tend to be either the group number, or the group number minus two.)

• Many of these ions have common or trivial names formed from the stem of the element name (the Latin name in some cases) plus the ending -ic or -ous. (-ic endings go with the higher possible charge, -ous endings go with the lower possible charge).

• The systematic names (also known as the Stock system) for these ions are derived by naming the metal first, followed in parentheses by the charge written in Roman numerals. For the metals below that typically form only one charge, it is not usually necessary to specify the charge in the compound name.

• For example, iron can form two possible ions, 2+ and 3+. The Fe2+ ion is known as the ferrous ion (common) or the iron(II) ion (systematic); the Fe3+ ion is known as the ferric ion (common) or the iron(III) ion (systematic).

The mercury(I) cation is a special case; it consists of two Hg+ ions joined together, and so is always found as Hg22+. (Hence, mercury(I) chloride is Hg2Cl2, not HgCl, while mercury (II) chloride is HgCl2.)

Ions of Some Transition Metals and Post-Transition Metals (Groups IVA and VA)

Main-Group Nonmetals (Groups IVA, VA, VIA, and VIIA)

Group IVA, VA, VIA, and VIIA nonmetals tend to form anions by gaining enough electrons to fill their valence shell with eight electrons. The charge on the anion is the group number minus eight. The anion is named by taking the element stem name and adding the ending -ide.

Ions of Some Nonmetals (Groups IVA - VIIA)

Polyatomic Ions

Polyatomic ions are ions that are composed of two or more atoms that are linked by covalent bonds, but that still have a net deficiency or surplus of electrons, resulting in an overall charge on the group. 

A metal plus a polyatomic ion yields an ionic compound.

Formulas and Names of Some Polyatomic Ions

There are some regularities in the names of these polyatomic ions.

• Thio- implies replacing an oxygen atom with a sulfur atom:

• Replacing the first element in the formula with another element from the same group gives a polyatomic ion with the same charge, and a similar name:

* But note that nitrogen does not follow this pattern (i.e., nitrate, NO3-)

• Some nonmetals form a series of polyatomic ions with oxygen (all having the same charge): ClO-, hypochlorite; ClO2-, chlorite; ClO3-, chlorate; ClO4-, perchlorate.
  • The -ate forms (formula and charge) must be memorized.  In some cases, the -ate form has three oxygens, and in some cases four oxygens.  The charge is the same for the entire series.
  • The -ite form has one less oxygen that the -ate form.
  • The hypo- stem -ite form has two less oxygens than the -ate form.
  • The per- stem -ate form has one more oxygen than the -ate form.
  • The -ide form is the monatomic anion (see Main-Group Nonmetals)
  • The general rules for such series are summarized in the table below:

Examples

Writing Formulas of Ionic Compounds

1. The cation is written first, followed by the monatomic or polyatomic anion.
2. The subscripts in the formula must produce an electrically neutral formula unit. (That is, the total amount of positive charge must equal the total amount of negative charge.)
3. The subscripts should be the smallest set of whole numbers possible.
4. If there is only one of a polyatomic ion in the formula, do not place parentheses around it; e.g., NaNO3, not Na(NO3). If there is more than one of a polyatomic ion in the formula, put the ion in parentheses, and place the subscript after the parentheses; e.g., Ca(OH)2, Ba3(PO4)2, etc.

Remember the Prime Directive in writing formulas:
Ca(OH)2 � CaOH2 !

Examples

Nomenclature of Ionic and Covalent Compounds

1. Binary Ionic Compounds Containing a Metal and a Nonmetal. 

A binary compound is a compound formed from two different elements. There may or may not be more than one of each element. A diatomic compound (or diatomic molecule) contains two atoms, which may or may not be the same.

Metals combine with nonmetals to give ionic compounds. When naming binary ionic compounds, name the cation first (specifying the charge, if necessary), then the nonmetal anion (element stem + -ide).

Do NOT use prefixes to indicate how many of each element is present; this information is implied in the name of the compound.

Examples

1. Ionic Compounds Containing a Metal and a Polyatomic Ion.

Metals combine with polyatomic ions to give ionic compounds. Name the cation first (specifying the charge, if necessary), then the polyatomic ion as listed in the table above (or as derived from the rules which were given).

Do NOT use prefixes to indicate how many of each element is present; this information is implied in the name of the compound.

Examples

1. Acids and Acid Salts.

Acids are compounds in which the "cation" is H+. (These are not really ionic compounds, but we'll get into that later.) These can be named as compounds as in the previous cases, e.g., HCl is "hydrogen chloride", but are more frequently given special "acid names" (especially when dissolved in water, which is most frequently the case.) The word "hydrogen" is omitted, the word "acid" is added to the end; the suffix is changed as shown below:

Examples

Acid salts are ionic compounds that still contain an acidic hydrogen, such as NaHSO4. In naming these salts, specify the number of acidic hydrogens in the salt. For instance:

Examples

The prefix bi- implies an acidic hydrogen: thus, NaHCO3 is sodium bicarbonate (or sodium hydrogen carbonate); NaHSO3 is sodium bisulfite (or sodium hydrogen sulfite), etc.

1. Binary Covalent Compounds Between Two Nonmetals.

Two nonmetals combine to form a covalent or molecular compound (i.e., one that is held together by covalent bonds which result from the sharing of electrons).

In many cases, two elements can combine in several different ways to make completely different compounds. (This cannot happen with ionic compounds, except in the cases of metals that can form more than one charge.) For instance, carbon can share electrons with one oxygen to make CO (carbon monoxide), or with two oxygens to make CO2 (carbon dioxide). For this reason, it is necessary to specify how many of each element is present within the compound.

• The formula is written with the more electropositive element (the one further to the left on the periodic table) placed first, then the more electronegative element (the one further to the right on the periodic table).

[Important exception: when the compound contains oxygen and a halogen, the halogen is placed first. If both elements are in the same group, the one with the higher period number is named first.]

• The first element in the formula is given the neutral element name, and the second one is named by replacing the ending of the neutral element name with -ide. A prefix is used in front of each element name to indicate how many atoms of that element are present:

• If there is only one of the first element in the formula, the mono- prefix is dropped.

Examples

1. Hydrocarbons.

Hydrocarbons contain only carbon and hydrogen, and are the simplest type of organic compound (a compound containing carbon). 

Alkanes contain only carbon-carbon single bonds, and are the simplest of the hydrocarbons. 

The simplest of the alkanes are the straight-chain alkanes, in which all of the carbon atoms are linked together in a line, with no branches. (They don't get simpler than that!) 

Alkanes have the general formula CnH2n+2, and are the constituents of several important fuels, such as natural gas and gasoline.

Organic chemistry has a completely different set of rules for nomenclature; straight-chain alkanes are named using a prefix plus the suffix -ane. Notice that after C4, the prefixes are the same as those listed above for binary covalent compounds.

(Because of the tremendous variety of possible organic compounds [over six million, and still counting], the rules for naming structures more complex than the staight-chain alkanes are much more elaborate than those that those we've seen so far, but those rules will be discussed when you take organic chemistry.) 

Molecular Masses from Chemical Formulas

The molecular mass, or molecular weight of a compound (measured in atomic mass units, amu) is obtained by adding up the atomic masses of all of the atoms present within a unit of the substance. 

For ionic compounds, the term formula mass or formula weight is used instead, since there aren't really any molecules present.

The molecular/formula mass is numerically equal to the mass of one mole of the substance.

For example, the molecular weight of water would be obtained by the following process:

Molecular mass of H2O = (2 x atomic mass of H) + (1 x atomic mass of O)
                                       = (2 x 1.00797) + (1 x 15.9994) amu
                                       = 18.02 amu

References

John McMurry and Robert C. Fay, Chemistry, 4th ed. Upper Saddle River, NJ:  Pearson/Prentice Hall, 2004, p. 56-63.

George E. Shankle & Harold W. Peterson, Laboratory Manual for Chemistry 1411.  University publication at Angelo State University, San Angelo, TX  76909, p. 27-31.

What are inorganic acids called?

Which of the following is an example of inorganic acid?

Why is carbonic acid an inorganic acid?

Is acids an inorganic compound?