What are the formula for the compounds?

How do we find the chemical formula of ionic compounds, intermetallic compounds, organic compounds, and ceramic compounds?

• There is an explanation that formula of ionic compounds are only made depending on their ion ratios. Please clarify Please answer even though you know atleast one of them.

• Answer:

  The chemical formula for Ionic compounds does indeed depend on the respective charges. For example: NaCl is NaCl because the participating ionic species in this compound are Na+Na+ Na^+ and Cl−Cl− Cl^- . On the other hand Cr2O72−Cr2O72− Cr_2O_7 2^- is such because the participating species are Cr6+Cr6+Cr6^+ and O2−O2−O2^-. Regarding inter-metallic compounds:  The chemical formula of such compounds are determined by mass spectrometry and structure determination. There is no FIXED formulation for determining the ratio of metallic species present in an inter-metallic compound, unless you go about analysing the compound itself. This is because the intermetallic compounds are formed by non-directional Metallic bonds, which can be formed by any two metallic species or between any number of metallic species at once, thus, rendering the compounds subjective to multiple bind sites. For example the intermetallic compounds of Fe come to my mind: Orthorhombic cementite ( Fe3CFe3CFe_3C); Hexagonal closed packed (ε) carbide (Fe2-3C) and monoclinic carbide ( Fe5C2Fe5C2 Fe_5C_2 ). Regarding Organic compounds: The determination of chemical formula of organic compounds is pretty straight forward and you can say fuss-proof (unless your reaction mechanism is incorrect). The EXACT formulae of organic compounds are however determined by NMR spectroscopy. Here is an example of NMR spectra for http://en.wikipedia.org/wiki/Strychnine: Regarding Ceramic compounds: The chemical formula of ceramic compounds is similar to that of covalently bonded compounds and can be determined by the basic Valency-exchange method taught in middle school.