Physical Properties of Matter

Physical Properties of Matter

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Physical properties are any properties of matter which can be perceived or observed without changing the chemical identity of the sample. In contrast, chemical properties are those that can only be observed and measured by performing a chemical reaction, thus changing the molecular structure of the sample.

Because physical properties include such a wide array of characteristics, they are further classified as either intensive or extensive and either isotropic or anisotropic.

Intensive and Extensive Physical Properties

Physical properties may be classified as either intensive or extensive. Intensive physical properties do not depend on the sample's size or mass. Examples of intensive properties include boiling point, state of matter, and density. Extensive physical properties depend on the amount of matter in the sample. Examples of extensive properties include size, mass, and volume.

Isotropic and Anisotropic Properties

Physical properties are isotropic properties if they do not depend on the orientation of the specimen or direction from which it is observed. The properties are anisotropic properties if they do depend on the orientation. While any physical property could be assigned as isotropic or anisotropic, the terms are usually applied to help identify or distinguish materials based on their optical and mechanical properties. For example, one crystal might be isotropic with respect to color and opacity, while another might appear a different color, depending on the viewing axis. In a metal, grains might be distorted or elongated along one axis compared with another.

Examples of Physical Properties

Any property you can see, smell, touch, hear or otherwise detect and measure without performing a chemical reaction is a physical property. Examples of physical properties include:

  • color
  • shape
  • volume
  • density
  • temperature
  • boiling point
  • viscosity
  • pressure
  • solubility
  • electric charge
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Physical Properties of Ionic vs. Covalent Compounds

The nature of chemical bonds plays a role in some of the physical properties that may be displayed by a material. The ions in ionic compounds are strongly attracted to other ions with opposite charge and repelled by like charges. Atoms in covalent molecules are stable and not strongly attracted or repelled by other parts of the material. As a consequence ionic solids tend to have higher melting points and boiling points, compared with low melting and boiling points of covalent solids. Ionic compounds tend to be electrical conductors when they are melted or dissolved, while covalent compounds tend to be poor conductors in any form. Ionic compounds are usually crystalline solids, while covalent molecules may exist as liquids, gases, or solids. Ionic compounds often dissolve in water and other polar solvents, while covalent compounds are more likely to dissolve in nonpolar solvents.

Physical Properties vs. Chemical Properties

Chemical properties encompass those characteristics of matter which can only be observed by changing the chemical identity of a sample, which is to say, by examining its behavior in a chemical reaction. Examples of chemical properties include flammability (observed from combustion), reactivity (measured by readiness to participate in a reaction), and toxicity (demonstrated by exposing an organism to a chemical).

Chemical and Physical Changes

Chemical and physical properties are related to chemical and physical changes. A physical change only alters the shape or appearance of a sample and not its chemical identity. A chemical change is a chemical reaction, which rearranges a sample on a molecular level.

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