Properties and Conditions
H.I. Feinstein

Matter is described, identified, tested, and evaluated by studying its charactersitics under known conditions. These charactersitics or properties, as they are called, may be divided into many classes. Schemes for such classification, however, may not all be based on the same criteria, and even if they are, differences are bound to arise in definition or interpretation of these criteria. For these reasons, in the following classification there is considerable overlapping so that some properties and some condiitons could, with equal justification, be placed in other classes.



These can be determined independantly of other substances and without a change in composition, although a structural change may occur. Physical properties may be subdivided as follows:

     A.  Mechanical
           Density and specific gravity
           Scratch hardness and indentation hardness
           Tensile strength
           Surface tension

     B.  Thermal
           Melting point (freezing point)
           Softening point or range
           Boiling point
           Critical temperature
           Critical pressure
           Critical volume
           Triple point temperature
           Specific heat capacity
           Molar heat capacity
           Heat of fusion
           Heat of vaporization
           Vapour pressure
           Heat of sublimation
           Heat of transition
           Heat conductivity
           Linear and cubical coefficient of expansion
           Flash point
           Fire point
           Autoignition temperature

      C. Optical
           Absorption spectrum
           Refractive index

      D. Electrical and Magnetic
           Elecrtical conductivity and resistivity
           Ionization energy
           Dielectric constant

      E. Acoustic
          Sound absorption coefficient

       Atomic number
       Mass number
       Atomic mass
       Isotopic composition
       Half-lives of radioactive nuclides
       Nuclear reactions


These determine the ability of a substance to change into one or more other substances.  These other substances have diffenr compositions and different properties. Chemical properties are concerned with such questions as:

       1.  Does the substance support combustion?
       2.  Is it flammable, combustile, or explosive?
       3.  Is it corrosive or corrodible?
       4.  Is it stable or unstale, inert or reactive?
       5.  Is it an oxidizing or reducing agent?
       6.  In general, how does it behave by itself and in contact with other substances and
            under what conditions?

       Heat of specified reactions
       Heat of formation
       Heat of combustion
       Heat of solution
       Free energy of formation


These have an effect on the human senses, especially taste and smell. These properties are often employed in the examination of food accessories.

   A    Physical Senses
         1. Sight
         2. Touch
         3.  Hearing

   B   Chemical Senses
         1. Taste
         2. Smell



These are properties which are equal to the sum of the properties of the atoms and the linkages in a molecule. For example: in inorganic chemsitry the properties of a salt are the sum of the properites of the ions. Molar volue is partly an additive property.


These are properties of a solution that are dependant upon the number of dissolved particles, whether ions or molecules, and not upon their nature.

         Vapour pressure depression
         Boiling point elevation
         Freezing point depression
         Osmotic pressure

         These depend upon the arrangement of the atoms in the molecule.
         Optical activity
         Dipole moment
         Refractive index


These are accidental characteristics of a particular specimen only such as length, width, volume, mass, internal energy, and shape. Attributes are sometimes called extensive properties which depend upon the amount of substance involved.


These are qualitites which can be more or less changed at will and which must be stated or understood when the properties of a substance are described, since such properties are dependant upon the conditions.

A.  Temperature affects many properties, such as
      1.  Density, especially of gases.
      2.  Crystal structure. The stable crystal system of sulphur is orthorhombic below 95.4oC
                                      and monoclinic above.
      3.  Change in electrical conductivity.
      4.  Rate of reaction.
      5.  Colour (thermochromic)  Some substances are known to change colours as their
           temperature changes.

                                    Some Thermochromic Compounds
           Compounds                 Colour                                Transition
                                     Cold            Hot                         temperature
              ZnO                  white          yellow                         ~250oC
              WO3                 yellow        dark orange
              HgI2                  red             yellow                        130oC
              Cu2HgI4            red             brownish-black          60-70oC
              Ag2HgI4            yellow        blood-red                   40-50oC

B.  Pressure  affects properties, such as
     1. Density (especially of gases).
     2. Rate of reaction since this is dependant upon concentration. This is especially important in          gaseous reactions.

C.  Electric charge on a particle determines its behaviour in an electric field and in the presence
      of other charged particles. A charged atom (ion) has different properties from the neutral
      atom.  For example, the sodium ion, Na+, is relatively inert, whereas sodium metal, Nao,
      is very reactive.

D.  Concentration affects properties, such as

1. Odour. Methyl benzoate is unpleasant in concentrated form but diluted it has the odour of new-mown hay.
2. Toxicity. Fluoride in water in a concentration of 1 ppm gives some protection against dental caries. Higher concentrations give rise to a condition known as mottled enamel.  In large doses fluoride is toxic.
3.  Rate of reaction.
4.  Colligative properties. The freezing point of water containing antifreezes, for example, will depend upon the concentration of the antifreeze.

E. Velocity.  According to the theory of relativity the mass of a particle will vary with its velocity.

                              m = mo / ( 1 - v2/c2 )-2

where m is the mass of the aprticle moving with velocity v with respect to the observer, mo is the mass at rest with respect to the observer and c is the velocity of light.  It is readily seen that a particle travelling with the speed of light should have infinite mass.

 F.  Direction
      1. The refractive index of certain transparent crystals varies with the direction of vibration of
          the light as it travels through the substance.  For example, calcite may show a refractive
          index of 1.658 for light vibrating in one direction nad 1.486 for light vibrating in another.

      2. Cleavage of crystals is often a directional property. For example, mica cleaves in thin sheets.

      3.  Hardness of different faces of a crystal may be different. For example the octahedral faces
           of diamond are harder than the cubical faces.  The dodecahedral faces are intermediate
           in hardness.

      4.  The observed colour may vary depending upon whether observed by reflected or
           transmitted light. For example, gold is yellow by reflected light but green by transmitted
           light (gold leaf).

      5.  The linear coefficient of expansion of crystalline substances may not be the same in all
           directions.  This is the reason many glasses shatter when subjected to rapid temperature

G.   Particle size may affect properties
      1. A colloidal gold dispersion appears violet if the particles of dispersed phase are relatively
          large and red if small. Metals in finely divided form often appear black, for example,
          platinum, silver and mercury.

      2. Silica gel (large surface area) has a greater adsorptive capacity than silica sand.

      3.  Platinum black is a better catalyst than bulk platinum.

      4.  The solubility of fine precipitates is greater than coarse precipitates. For example
           strontium sulphate which is almost insoluble anyways will dissolve slightly better is
           finely ground.

H.   Catalyst
       The presence of a catalyst may make a theoretically possible reaction practical.

I.     Impurities
       The presence of small amounts of impurities may produce a profound change in properties.
       For example, rubies are deep red gems which is aluminum oxide (Al2O3, white or
       colourless) containing small amounts of chromium oxide (Cr2O3, green).