Chemical compound

Definition and Types of Chemical Compounds

  • A chemical compound is composed of many identical molecules containing atoms from more than one chemical element.
  • A compound can be transformed into a different substance by a chemical reaction.
  • There are four major types of compounds: molecular compounds, ionic compounds, intermetallic compounds, and coordination complexes.
  • Non-stoichiometric compounds form a disputed marginal case.
  • Chemical compounds have a unique chemical structure held together by chemical bonds.

History and Concept of Chemical Compounds

  • The term compound has been in use since at least 1724.
  • Isaac Watts used the term in his book 'Logick' to describe substances that are composed of multiple elements.
  • The concept of elements being combined to form compounds has evolved over time.
  • Early beliefs included the four elements (fire, air, earth, and water) and later expanded to include substances like spirit, salt, sulfur, water, and earth.
  • The understanding of compounds has been refined through experimental philosophy.

Chemical Formulas and Identification of Compounds

  • A chemical formula specifies the number of atoms of each element in a compound molecule.
  • Chemical formulas use standard chemical symbols with numerical subscripts.
  • Many chemical compounds have a unique CAS number assigned by the Chemical Abstracts Service.
  • Globally, over 350,000 chemical compounds have been registered for production and use.
  • Chemical formulas and CAS numbers provide a standardized way to identify and classify compounds.

Types of Chemical Compounds (Molecules, Ionic Compounds, Intermetallic Compounds)

  • A molecule is a group of two or more atoms held together by chemical bonds.
  • Molecules can be homonuclear (consisting of atoms of one element) or heteronuclear (composed of more than one element).
  • Molecules are the smallest units of a substance that retain its physical and chemical properties.
  • Examples of molecules include oxygen (O2) and water (H2O).
  • Molecules are held together by covalent bonds.
  • Ionic compounds are composed of ions held together by electrostatic forces.
  • They consist of cations (positively charged ions) and anions (negatively charged ions).
  • Ionic compounds can be simple ions (e.g., sodium chloride) or polyatomic species (e.g., ammonium carbonate).
  • Individual ions in an ionic compound are not considered part of molecules but form a continuous three-dimensional network.
  • Ionic compounds have high melting and boiling points, are hard and brittle, and can conduct electricity when melted or dissolved.
  • Intermetallic compounds are ordered solid-state compounds formed between metallic elements.
  • They are generally hard and brittle, with good high-temperature properties.
  • Intermetallic compounds have unique crystal structures and exhibit specific properties.
  • They are different from alloys, which are mixtures of metals.
  • Intermetallic compounds play a significant role in various fields, including materials science and engineering.

Nomenclature and Variability of Compounds, Bonding and Forces, Reactions

  • Nomenclature differentiates substances, including non-stoichiometric examples, from chemical compounds.
  • Some solid chemical substances, such as silicate minerals, do not have simple formulae reflecting fixed ratios of elements.
  • Non-stoichiometric substances can result from foreign elements trapped within crystal structures or perturbations in structure.
  • Isotopes of constituent elements can also cause variability in the ratio of elements by mass.
  • Non-stoichiometric compounds form a significant portion of the Earth's crust and mantle.
  • Compounds are held together through different types of bonding and forces.
  • The types of bonds in compounds depend on the elements present.
  • London dispersion forces are the weakest intermolecular force and are responsible for condensing nonpolar substances.
  • Covalent bonds involve the sharing of electrons between atoms.
  • Ionic bonding occurs when valence electrons are completely transferred between elements.
  • Chemical reactions involve the conversion of compounds into different chemical compositions.
  • Bonds between atoms in interacting compounds are broken and reformed to create new associations.
  • Chemical reactions can be represented schematically as AB + CD AD + CB.
  • Reactions involve unique atoms and compounds.
  • Chemical reactions are fundamental to the study of chemistry.

Chemical compound Data Sources

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