Chemical nomenclature

Chemical nomenclature

Inorganic Compounds

Inorganic compounds consist of the remaining compounds divided in to two groups; Ionic compounds and Molecular compounds

Ionic Compounds

The names of ionic compounds are based on the names of the ion which they are composed. For example, NaCl is called sodium chloride after the Na⁺ or sodium ion, and the Cl^- or chloride ion. The positive ion is always named first and listed first in writing the formula for the compound. The negative ion is named and written last. To see how the names of these ions arise, consider first the naming of positive ions, also called cations. Ions may be monatomic (composed of a single atom) or polyatomic (formed from two or more atoms). Monatomic cations are most commonly formed from metallic elements.
These ions take the name of the element itself:

Na⁺ Sodium ion

Zn⁺ Zinc ion

Al³⁺ Aluminum ion

If an element can form more than one positive ion, the positive charge of the ion is indicated by a Roman numeral in parentheses following the name of the metal:

Fe²⁺ Iron(II) ion

Fe³⁺ Iron(III) ion

Cu⁺ Copper(I) ion

Cu²⁺ Copper(II) ion

An older method still widely used for distinguishing between two differently charged ions of a metal is to apply the endings –ous or –ic. These endings represent the lower and higher charged ions, respectively, They are added to the root of the Latin name of the element:

Fe²⁺ Ferrous ion

Fe³⁺ Ferric ion

Cu⁺ Cuprous ion

Cu²⁺ Cupric ion

Negative ions are called anions. Monatomic anions (those derived from a single atom) are most commonly formed from atoms of the nonmetallic elements. They are named by dropping the ending of the name of the element and adding the ending -ide:

H^- Hydride ion

F^- Fluoride ion

O^2- Oxide ion

S^2- Sulfide ion

Many polyatomic anions contain oxygen. Anions of this kind are referred to as oxyanions. A particular element such as sulfur may form more than one oxyanion. When this occurs, there are rules for indicating the relative numbers of oxygen atoms in the anion. When an element forms only two oxyanions, the name of the one that contains more oxygen ends in -ate; the name of the one with less oxygen ends in -ite:

NO₂^- Nitrite ion

SO₃^2- Sulfite ion

NO₃^- Nitrate ion

SO₄^2- Sulfate ion

When the series of anions of a given element extends to three or four members, as with the oxyanions of the halogens, prefixes are also employed. The prefix hypo- indicates less oxygen, and the prefix per- indicates more oxygen:

ClO^- Hypochlorite ion

ClO₂^- Chlorite ion

ClO₃^- Chlorate ion

ClO₄^- Perchlorate ion

Molecular Compounds

The procedures for naming binary (two element) molecular compounds are similar to those for naming ionic compounds. In these molecular compounds it is possible to associate a more positive nature with one element in the molecule and a more negative nature with the other element. The element with the more positive nature is named first and also appears first in the chemical formula. The second element is named with an -ide ending. For example, the name for HCl is hydrogen chloride. (this is the name used when referring to the pure compound; water solutions of HCl are referred to as hydrochloric acid.)

Often a pair of elements can form several different molecular compounds. For example, carbon and oxygen form CO and CO₂. To distinguish these compounds from one another, the prefixes given below are used to denote the numbers of atoms of each element present.

Prefix	Meaning
Mono-	1
Di-	2
Tri-	3
Terta-	4
Penta-	5
Hexa-	6
Hepa-	7
Octa-	8

Thus CO is called carbon monoxide, and CO₂ is called carbon dioxide. When the prefix ends in a and the name of the anion begins with a vowel (such as oxide), the a is often dropped.

Organic Compounds

Organic compounds contain carbon, usually in combination with hydrogen, oxygen, nitrogen, or sulfur. Organic compounds were first associated only with plants and animals. However, a great number of organic compounds have now been prepared that do not occur in nature.

Alkynes

Alkynes are unsaturated organic compounds with at least one carbon-carbon triple bond. In nature, alkynes are found in numerous plants and fruits, and most compounds can be readily synthesized industrially or in a laboratory.

Physical Properties

Overall the physical properties of alkynes are somewhat similar to those of alkenes. Alkynes have higher boiling points than the corresponding alkanes and alkenes:

Compound: Butane < Butene < Butyne

Boiling point: Low → High

Most alkynes have low density and low solubility in water; conversely, alkynes are nonpolar and are readily dissolved in organic colvents. At room temperature, compounds with lower molecular weights are gases.