The Physical Properties of Substances

Example 1-1. Classify the following materials as homogeneous or heterogeneous, substance or solution, compound or element  

The study of the properties of substances constitutes an important part of chemistry, because their properties determine the uses to which they can be put. 

The physical properties are those properties of a substance that can be observed without chauf ing the substance into other substances. 

Let us again use sodium chloride, common salt, as an example of a substance. We have all seen this substance in what appear to be different forms —table salt, in fine grains salt in the form of crystals a quarter of an inch in diameter, for use with ice for freezing ice cream and natural crystals of rock salt an inch or more across. Despite their obvious difference, all of these samples of salt have the same fundamental properties. 

There are other properties besides density and solubility that can be measured precisely and expressed in numbers. Such another property is the melting point, the temperature at which a solid substance melts to form a liquid. On the other hand, there are also interesting physical properties of a substance that are not so simple in nature. One such property is the malleability of a substance —the ease with which a substance can be hammered out into thin sheets. A related property is the ductility—the ease with which the substance can be drawn into a wire. Hardness is a similar property we say that one substance is less hard than the second substance when it is scratched by the second substance. The color of a substance is an important physical property. 

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THE EFFECT OF THE HYDROGEN BOND ON THE PHYSICAL PROPERTIES OF SUBSTANCES... 

Richet C. On the relationship between the toxicity and the physical properties of substances. Compt Rend Soc Biol 1893 (9)5 775-6. 

The physical properties of substances do not involve chemical changes. Color (see Textbox 17) and crystal structure (see Textbox 21), for example, are physical properties that are characteristic of a substance that serve to identify most substances. Other physical properties, such as density, hardness (see Table 3), refractive index (see Table 19), and heat capacity (see Table 101), are also useful for characterizing and identifying substances as well as distinguishing between different substances. 

In this section, you have used Lewis structures to represent bonding in ionic and covalent compounds, and have applied the quantum mechanical theory of the atom to enhance your understanding of bonding. All chemical bonds—whether their predominant character is ionic, covalent, or between the two—result from the atomic structure and properties of the bonding atoms. In the next section, you will learn how the positions of atoms in a compound, and the arrangement of the bonding and lone pairs of electrons, produce molecules with characteristic shapes. These shapes, and the forces that arise from them, are intimately linked to the physical properties of substances, as you will see in the final section of the chapter. 

Forces that influence the physical properties of substances are called intermolecular forces. These are forces of attraction and repulsion that act between molecules or ions. 

Dipole-dipole, ion-dipole, and dispersion forces are collectively known as van der Waals forces. Johaimes Diederick van der Waals (1837-1923) received the 1910 Nobel Prize in physics for his work on fluids. We have seen how hydrogen bonding and van der Waals forces affect the physical properties of substances, and more is said about these forces as we examine the different states of matter. 

The physical properties of substances these depend on the properties of individual molecules and on how the molecules interact in the bulk material. For example, the strength and melting point of a polymer (e.g. a plastic) depend on how well the molecules fit together and on how strong the forces between them are. People who investigate things like this work in the field of materials science. 

Influence of Desiccation upon the Physical Properties of Substances.—Liquids that have been thoroughly desiccated by exposure to phosphorus pentoxide for several years manifest a decided elevation in boiling-point, ranging in extent from 80° to 60° C, This is well illustrated by the following data 1... 

As we previously learned, mixtures are not pure substances. In order to obtain one of the components in a mixture, we need to separate them. The separation of mixtures can only be possible when we use the physical properties of substances. 

Compare the physical properties of substances that have different bond types, and relate bond types to electronegativity differences. 

The fact that substances can change form, as in the example of water changing to steam, is another important concept in chemistry. If you review what you just learned about physical properties of substances, you can see that because the particular form of a substance is a physical property, changing the form introduces or adds another physical property to its list of characteristics. In fact, resources that provide tables of physical and chemical properties of substances, such as the CRC Handbook of Chemistry and Physics, generally include the physical properties of substances in all of the states in which they can exist. 

Skill 14.2 Demonstrating knowledge of methods and equipment used for measuring the physical properties of substances... 

Interparticle forces determine many of the physical properties of substances. Interparticle forces between dipoles such as water are especially strong. 

Chemists are concerned with the physical properties of substances. Are they solids, liquids, or gases How much energy do they contain Chemists are also concerned with chemical properties. Can they be transformed to other substances on heating or irradiating What are the detailed mechanisms of these transformations ... 

A lecturer discussing the physical properties of substances at very low temperatures, remarked it appears that the specific heat, decreasing temperatures, 6, at a rate proportional to the specific heat of the substance itself . Set up the differential equation to represent this law and put your result in a form suitable for experimental verification. Ansr. (log r0 - log[Pg.372]

The physical properties of substances usually result from the strength of the intermolecular forces at work between its molecules. The reactivity of substances is based on stability considerations that are often a result of high or low electronegativity. The reactivity of large molecules is often localized to the most polar regions or charged regions of the molecule. 

Chemists measure the physical properties of substances. They may take new compounds and measure the melting points and boiling points. They may measure the strength of a new polymer strand or determine the octane rating of a new gasoline. 

Many reference books list the physical properties of substances. You should consult Technique 4 for a complete discussion on how to find data for specific compounds. The works most useful for finding lists of values for the nonspectroscopic physical properties include... 

Others have defined physical chemistry as that field of science that applies the laws of physics to elucidate the properties of chemical substances and clarify the characteristics of chemical phenomena. The term physical chemistry is usually applied to the study of the physical properties of substances, such as vapor pressure, surface tension, viscosity, refractive index, density, and crystallography, as well as to the study of the so-called classical aspects of the behavior of chemical systems, such as thermal properties, equilibria, rates of reactions, mechanisms of reactions, and ionization phenomena. In its more theoretical aspects, physical chemistry attempts to explain spectral properties of substances in terms of fundamental quantum theory, the interaction of energy with matter, the nature of chemical bonding, the relationships correlating the number of energy states of electrons in atoms and molecules with the observable properties shown by these systems, and the electrical, thermal, and mechanical effects of individual electrons and protons on solids and liquids. ... 

The physical properties of substances may be predicted from the type of bonding present. 

At the end of this chapter, you will be able to answer questions about the physical properties of substances used in the treatment and prevention of kidney stones [ H Page 527]. 

Use of specific, intensive state variables can in many cases simplify calculations and analyses. Usually, tables of the physical properties of substances list specific substance values, i.e. intensive values that are independent of the size of the chosen system. 

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