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
| Reference | URL |
|---|---|
| Glossary | https://www.alternix.com/blogs/glossary-of-terms/chemical-compound |
| Wikipedia | http://en.wikipedia.org/wiki/Chemical_compound |
| Wikidata | https://www.wikidata.org/wiki/Q11173 |
| Knowledge Graph | https://www.google.com/search?kgmid=/m/0129f4 |
