Physical and Chemical Properties

Physical Properties and Changes of Matter

Those attributes whereby one substance may be distinguished from another are termed properties. A physical property is a characteristic of matter which involveth no alteration in its chemical constitution. Common examples of such qualities include density, colour, hardness, the temperatures of liquefaction and ebullition, and electrical conductivity.

Certain of these attributes, such as density and colour, may be observed whilst the substance remaineth in a constant state. Others, however, are manifest only as the matter undergoeth a physical change, such as the melting of iron or the freezing of water. A physical change is an alteration in the state or properties of matter without any accompanying change in its chemical composition or the identity of its constituent substances.

A physical change is observed when wax undergoeth liquefaction, when sugar findeth dissolution within coffee, or when steam condenses to form liquid water. Further instances of such changes include the magnetisation and demagnetisation of metallic bodies, and the reduction of solid matter to powder by grinding—the latter of which may at times produce a perceptible alteration in colour. In every such case, though there be a change in the physical state, form, or properties of the substance, the fundamental chemical constitution remaineth unchanged.

Wax melting process.

Water distillation process

The transformation of one species of matter into another, or the inherent resistance to such alteration, constituteth a chemical property. Included amongst these properties are flammability, toxicity, acidity, diverse forms of reactivity, and the heat of combustion.

By way of illustration, iron combineth with oxygen in the presence of moisture to form rust, while chromium exhibiteth no such oxidation. Furthermore, whereas nitroglycerine is held to be exceedingly dangerous by reason of its explosive instability, neon poseth negligible hazard, being of a notably unreactive and inert disposition.

For the identification of a chemical property, the observer must witness a chemical change. Such an alteration invariably resulteth in the production of one or more species of matter, differing in their fundamental essence from the substances present prior to the transformation.

The formation of rust is rightly termed a chemical change, for the rust itself is a distinct form of matter, quite unlike the iron, oxygen, and water from which it was derived. In a similar manner, the detonation of nitroglycerine constituteth a chemical change, as the resultant gases are entirely different in kind from the parent substance. Further instances of chemical change are to be found in the laboratory—as seen in the vigorous action of nitric acid upon copper—as well as in all modes of combustion, and in the various processes whereby food is cooked, digested, or left to suffer the effects of putrefaction.

The properties of matter are found to reside within one of two distinct categories. Should a property depend upon the quantity of matter present, it is termed an extensive property. Mass and volume serve as the primary examples of this class; for instance, a gallon of milk possesseth a greater mass and volume than doth a single cup. The value of such an extensive property is found to be directly proportional to the amount of matter under consideration.

Conversely, if the property of a sample be independent of the quantity of matter present, it is designated an intensive property. Temperature provideth an apt illustration of this principle. Should a gallon of milk and a cup of milk each reside at a temperature of 20°C, their combination shall result in a larger volume of milk which nonetheless maintaineth the temperature of 20°C.

Consider, furthermore, the related but distinct qualities of heat and temperature. A mere drop of hot cooking oil spattered upon the arm causeth but a brief and minor discomfort; yet, a pot of the same oil shall yield burns of a most severe nature. Whilst both the drop and the pot exist at the same temperature—this being an intensive property—the pot clearly containeth a far greater quantity of heat, which is an extensive property.

Whilst many elements differ dramatically in their chemical and physical properties, certain of their number exhibit strikingly similar behaviours. We may thus identify groups of elements which display common characteristics. For instance, many elements serve as excellent conductors of heat and electricity, whereas others prove to be poor conductors. Such properties allow the classification of elements into three distinct orders: metals, which conduct well; non-metals, which conduct poorly; and metalloids, which possess the attributes of both classes.

Periodic Table of Elements.