Origins of chemical symbols

The names of the elements are derived from various sources. Many are derived from Greek, Latin or German words that generally describe some properties of the elements. For example, the word ‘iodine’ is taken from the Greek word ‘iodes’, meaning violet-like. Iodine, indeed, is violet in vapor state. Some elements are named after the place of their discovery. For example, uranium is named after the planet Uranus, neptunium is named after the planet Neptune, and plutonium is named after Pluto.

Chemists use symbols as abbrevaiation of the names of elements. A symbol is a shorthand notation of the chemical names of the element. Every element has its own symbol.

To avoid giving identical symbol to two or more different elements a second letter or a letter outstanding in the name is added to the first letter. If two letters are used, the first letter is capitalized and the second one is written in small letter.

The symbols for the above elements are derived from their English names. The symbols of some elements are derived from their Latin names.

Chemical Formulas

Do you know the difference between CO and CO₂ in Chemistry?

The formula of a substance is the symbolic representation of its composition. Formulas can be classified as formulas of elements and formulas of compounds.

The formula of an element consists of one kind of symbol whereas the formula of a compound contains the symbols of two or more different elements.

The formulas of elements

Only a few elements such as the gases helium, neon and argon consist of single uncombined atoms that move about independent of one another. Other elements, such as the gaseous hydrogen, oxygen, nitrogen etc, consist of pairs of atoms, each moving as a single unit. The element phosphorus consists of units of four atoms. Sulfur consists of eight atoms. Such units are called molecules.

Writing formula of compounds

It is easy to write the formula of a compound if we know the combining power of the elements or polyatomic ions involved. The combining power of an element is its relative capacity to combine with other elements. This combining power of an element is called valence number. For example, in HCl one atom of chlorine combines with one atom of hydrogen, the valence number of chlorine is 1. Since one atom of oxygen combines with two atoms of hydrogen to form water, H₂O, the valence number of oxygen is 2. Similarly, one atom of nitrogen combines with three atoms of hydrogen to form ammonia, NH₃. Therefore, the valence number of nitrogen is 3.

Formulas of Binary Compounds

Binary compounds contain atoms of two different elements. Sodium chloride (NaCl), Hydrogen bromide (HBr) and Copper (II) oxide (CuO) are some examples of binary compounds. Binary compounds contain atoms of two different elements. Sodium chloride (NaCl), Hydrogen bromide (HBr) and Copper (II) oxide (CuO) are some examples of binary compounds.

Naming Compounds

The two constituent elements of binary compounds are usually metals and non-metals. For example, NaBr, CaO and AlCl₃. There are also binary compounds which consist of non-metallic elements only. For example, H₂O, CO₂ and NH₃.

Rules in Naming Binary Compounds:

• The name of a binary compound is the combination of the names of the two constituent elements.
• For binary compounds that consist of metals and non-metals, the metal is named first followed by the non-metal.
• The suffix -ide replaces the last letters of the name of the non-metal. For example, chlorine is changed to chloride.

The following guidelines are helpful in naming compounds with prefixes:

• The prefix “mono” may be omitted for the first element. For example, PCl₃ is named phosphorus trichloride, not monophosphorus trichloride. Thus the absence of a prefix for the first element usually means there is only one atom of that element present in the molecule.
• For “oxides”, the ending “a” in the prefix is sometimes omitted. For example, N₂O₄ is named dinitrogen tetroxide rather than dinitrogen tetraoxide.