MATTER

By: Ray Shelton

Definition of matter. Matter is anything that occupies space and has mass. Since density by definition involves both mass and volume (the space occupied by the mass), density is the fundamental property of matter. The density of matter is defined as the ratio of its mass to its volume. Since the mass and volume of matter depends upon the sample, these cannot be used separately to identify the kind of matter that it is. However, the ratio of the mass to the volume for a given substance is the same for every sample of that substance, provided they are measured under identical conditions. For example, the density of zinc is 7.14 gm/cm³ whether the sample is one gram or one thousand grams. Density is thus the defining numerical physical property of matter. The density of gases, for example, must be determined under the same conditions of temperature and pressure, which is usually 0°C and 1 atmosphere of pressure (STP, Standard Temperature and Pressure).

There are two kinds of density:
mass-density, which is defined as ρ = m/V,
where m = mass and V = volume;
weight-density, which is defined as D = w/V,
where w = the weight and V = volume.
Since weight is related to mass by w = mg, where g is the acceleration due to gravity, weight-density is related to mass-density by D = ρg.
The metric units of mass-density is grams per cubic centimeter (g/cm³) or kilograms per cubic meter (kg/m³), and the English units of weight-density is pounds per cubic inch (lb/in³). Since 1 kilogram = 1000 grams and 1 meter is 100 centimeters, then the density of 1 kg/m³ = 1000 g/(100 cm)³ = 10³ g/(10⁶ × cm³) = 10^-3 × g/cm³. That is, if the density is given in g/cm³, it must be multiplied by 1000 to give the density in kg/m³. For example, the mass-density of mercury is 13.6 g/cm³, which is 13.6 × 10³ kg/m³ or 13600 kg/m³.
The mass-density of some substances are given in the following table. Since temperature affects the density of gases (the affect is slight for liquids and solids), their densities are given at 0°C and at 1 atm of pressure, unless otherwise specified.

Note that the mass-density of water is very close to 1.00 g/cm³ at 4°C, where its mass-density is maximum. Now the weight-density of pure water at 4°C is 62.4 lb / ft³. Hence, its mass-density is ρ = D/g = 62.4 / 32.16 slugs / ft³ = 1.94 slugs/ft³. That is, 1 g/cm³ is equal to 1.94 slugs/ft³. Thus the mass-density in slugs/ft³ can be obtained by multiplying the mass-density in g/cm³ by 1.94.

The specific gravity or the relative density of a substance is defined as the ratio of the density of that substance to the density of some substance taken as a standard. Pure water, since its mass-density at 4°C is 1.00 g/cm³, is commonly taken as the standard. For gases either air or oxygen is used as the standard for the specific gravity. Thus, using water as the standard for specific gravity of solids or liquids, the mass-density in cgs units and the specific gravity of a substance have the same numerical values. Note that specific gravity has no units, that is, it is not a dimensional quantity, since it is by definition the ratio of two dimensional quantities in which their units cancel.

Weight-density is not an absolute property of matter, since the weight of body depends upon the strength of the gravitational field in which the body is placed. For instance, the weight-density of aluminum, measured on the moon, would be about 1/6 less than that measured on the earth, since the moon's gravity is 1/6 less than the earth's gravity and hence the weight of the same body on the moon would be 1/6 of its weight on the earth. Because of this relative character of weight-density, the term "density" is usually understood to mean mass-density.

Two views of matter. There are two ways that matter may be viewed: quantitatively or qualitatively.

1. Quantitative View. Matter, considered from the quantitative point of view, is called an object of matter. An object of matter is a definite piece of matter occupying a definite amount of space and having a definite amount of mass. It is sometimes called a physical body or, for short, a body. There are two classes of bodies:
   1. Heterogeneous Bodies. A body which consists of visible parts have different properties (density, color, hardness, etc.) is said to be heterogeneous (literally from the Greek, "of different kind"). Such bodies are also called mixtures. Mixtures are not uniform in composition; they may have variable proportions by weight of the components and may be separated into their homogeneous components by making use of the different physical properties of the components.
   2. Homogeneous Bodies. A body which does not consist of visible parts having different properties is said to be homogeneous (literally from the Greek, "of the same kind"). Under the most powerful microscope a homogeneous body are indistinguishable into parts having different properties. Homogenous bodies may be divided into two classes:
      (1) Solutions: a homogeneous body having a variable composition;
      (2) Pure Substances: a homogeneous body having a definite chemical composition.
2. Qualitative View. Matter considered from the qualitative point of view is called a kind of matter. A kind of matter is any variety of matter, all specimens of which posses the same properties. A kind of matter is called a substance. One substance is distinguished from another substance by its properties. There are two classes of substances:
   1. Elementary Substances or Elements. An element is a substance that cannot by ordinary chemical means be decomposed into or built up from two or more simpler substances. Elements can be divided into two classes:
      (1) Metals. A metal is an element which has high density, high tensile strength, metallic luster, silver or grayish-white color (copper and gold are exceptions), and is malleable, ductile, a good conductor of heat and electricity, and whose oxides in water form bases.
      (2) Non-metals. A non-metal is an element which has low density, low tensile strength, non-metallic luster, many characteristic colors, and is non-malleable, non-ductile, a poor conductor of heat and electricity, and whose oxides in water from acids.
   2. Compound Substances or Compounds. A compound is a substance which is made up of two or more different elements, in definite proportions by weight, having properties different from those of the elements of which it is composed. Compounds are divided into two classes:
      (1) Organic Compounds. Organic compounds are all compounds containing carbon; they are not necessarily found in or come from living organisms.
      (2) Inorganic Compounds. Inorganic compounds are all compounds not containing carbon.

Properties of Matter. A property of matter is a characteristic of a kind of matter by which it may be identified. There are two kinds of properties of matter.

1. Physical Properties. A physical property is a characteristic of matter which can be observed without changing the matter into some other kind of matter. There are two classes of physical properties:
   1. Specific Properties: those properties unaffected appreciably by the size of sample or state of subdivision.
      (1) Density.
      (2) Color.
      (3) Odor - can be considered a chemical property.
      (4) Taste - can also be considered a chemical property.
      The following properties are those characteristic of solids:
      (5) Luster
      (6) Tensile Strength.
      (7) Malleability: the ease with which a sample of the matter can be hammered into sheets.
      (8) Ductility: the ease with which a sample of the matter can be drawn into wire.
      (9) Melting Point.
      (10) Coefficient of thermal expansion.
      (11) Heat of fusion.
      (12) Heat of vaporization.
      (13) Thermal conductivity.
      (14) Electrical conductivity.
      (15) Magnetism.
      (16) Crystalline form - shape of crystal and cleavage.
      (17) Solubility - can also be considered a chemical property.
      (18) Viscosity: the ease with which a sample flows - mainly liquids.
      
   2. Non-specific Properties: those properties affected by size of the sample or state of subdivision.
      (1) Length.
      (2) Volume.
      (3) Shape.
      (4) Weight.
      (5) Mass.
2. Chemical Properties: chemical properties are those characteristics of a kind of matter that are related to its participation in chemical change. A chemical change is the process by which a substance is converted into another substance.

1. solid, which have definite shape and definite volume. A solid maintains a fixed shape and a fixed size and volume; even if a large force is applied to a solid, it does not easily change its shape and volume.
   
2. liquid, which have indefinite shape (it takes the shape of its container) but definite volume. Even though a liquid does not maintain a fixed shape, like a solid it is not easily compressible and its volume can be changed significantly only by a very large force.
   
3. gas, which have indefinite shape and indefinite volume (it takes the volume and shape of its container). A gas has neither a fixed shape or fixed volume; it expands to fill its container. For example, when air is pumped into an automobile tire, the air does not settled to the bottom of the tire like a liquid would, but fills the entire volume of the tire.

Some scientists have proposed that there is a fourth state of matter, which they have called plasma. Plasmas are very much like gases except that their constituent particles have become electrically charged and their behavior consequently strongly depends upon electromagnetic forces, in addition of the usual mechanical forces. But because plasmas do not exist under ordinary conditions on earth, they are unfamiliar to us, although nearly all matter in the universe as a whole is in a plasma state. In our discussion here of the mechanical properties of matter, we will ignore the plasma state and concentrate on the three more familiar terrestrial states of matter.

Since both liquids and gases do not maintain a fixed shape and each have the ability to flow, they are referred to collectively as fluids. Sometimes a clear line of division between solids and liquids can not be drawn; a material like pitch seems to be quite hard and rigid, but a piece of it will eventually change its shape and spread out on the surface upon which it rests. Glass also flows, although very slowly, and is often considered to be liquid. These substances are often referred to as amorphous solids to distinguish them from crystalline solids which have an ordered, periodic structure.