Basic Concepts

Elements and compounds


Elements and Compounds

Pure substances have an invariable composition and are composed of either elements or compounds.

Elements

"Substances which cannot be decomposed into simpler substances by chemical means".

Compounds

Can be decomposed into two or more elements.

 


Elements

Elements are the basic substances out of which all matter is composed.

Elements are known by common names as well as by their abbreviations. These consisting of one or two letters, with the first one capitalized. These abbreviations are derived from English or foreign words (e.g. Latin, German).

Element

Abbreviation

Carbon

C

Fluorine

F

Hydrogen

H

Iodine

I

Nitrogen

N

Oxygen

O

Phosphorus

P

Sulfur

S

Aluminum

Al

Barium

Ba

Calcium

Ca

Chlorine

Cl

Helium

He

Magnesium

Mg

Platinum

Pt

Silicon

Si

Copper

Cu (from cuprum)

Iron

Fe (from ferrum)

Lead

Pb (from plumbum)

Mercury

Hg (from hydrargyrum)

Potassium

K (from kalium)

Silver

Ag (from argentum)

Sodium

Na (from natrium)

Tin

Sn (from stannum)

 

Compounds

Compounds are substances of two or more elements united chemically in definite proportions by mass. For example, pure water is composed of the elements hydrogen (H) and oxygen (O) at the defined ratio of 11 % hydrogen and 89 % oxygen by mass.

The observation that the elemental composition of a pure compound is always the same is known as the law of constant composition (or the law of definite proportions). It is credited to the French chemist Joseph Louis Proust (1754-1826).


1996 Michael Blaber