Chemical substances

Chemical Substances

Chemical substances are forms of matter that have constant chemical composition and characteristic properties. They cannot be separated into components by physical separation methods, i.e., without breaking chemical bonds. Chemical substances can be simple substances, chemical compounds, or alloys.

Classification

Chemical substances can be classified into several categories:

Elements

Elements are pure chemical substances consisting of a single type of atom, distinguished by its atomic number, which is the number of protons in its atomic nucleus. Examples include oxygen (O), hydrogen (H), and iron (Fe).

Compounds

Compounds are substances formed when two or more elements are chemically bonded together. They have a fixed ratio of atoms and a specific chemical formula. Examples include water (H₂O), carbon dioxide (CO₂), and sodium chloride (NaCl).

Mixtures

Mixtures are combinations of two or more substances where each retains its own chemical identity and properties. Mixtures can be homogeneous (solutions) or heterogeneous. Examples include air (a mixture of gases) and saltwater.

Properties

Chemical substances have distinct physical and chemical properties that can be used to identify and classify them.

Physical Properties

Physical properties are characteristics that can be observed or measured without changing the substance's chemical identity. These include:

• Melting point
• Boiling point
• Density
• Color
• Solubility

Chemical Properties

Chemical properties describe a substance's potential to undergo chemical change or reaction by virtue of its composition. These include:

• Reactivity with other chemicals
• Flammability
• Acidity or basicity
• Oxidation state

Chemical Reactions

A chemical reaction involves the transformation of one or more substances into different substances. Chemical reactions are characterized by the breaking and forming of chemical bonds, leading to changes in the composition of matter. Reactions can be classified into several types, such as:

• Synthesis reaction
• Decomposition reaction
• Single displacement reaction
• Double displacement reaction
• Combustion reaction

Applications

Chemical substances are integral to various fields and industries, including:

• Pharmaceuticals: Development of drugs and medications.
• Agriculture: Fertilizers and pesticides.
• Manufacturing: Production of plastics, metals, and other materials.
• Food industry: Additives and preservatives.

Safety and Regulation

The handling and use of chemical substances are subject to strict regulations to ensure safety and environmental protection. Organizations such as the Environmental Protection Agency (EPA) and the Occupational Safety and Health Administration (OSHA) provide guidelines and standards for chemical safety.

See Also

• Periodic table
• Chemical bond
• Molecule
• Chemical formula

References

• "Chemistry: The Central Science" by Brown, LeMay, Bursten, Murphy, and Woodward.
• "Principles of Modern Chemistry" by Oxtoby, Gillis, and Campion.