Dot between the molecular formula of compounds

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Discussion Overview

The discussion revolves around the meaning of the dot notation in molecular formulas, particularly in the context of compounds that are represented as mixtures, such as hydrates and certain mineral compositions. The scope includes conceptual clarification and technical explanation of chemical notation.

Discussion Character

  • Conceptual clarification, Technical explanation, Debate/contested

Main Points Raised

  • One participant notes that the dot indicates a stoichiometric mixture of substances, suggesting that the components may or may not be separable.
  • Another participant proposes that the dot generally refers to non-covalently associated substances, particularly in the case of hydrates.
  • A further contribution challenges the idea that the dot notation is exclusive to hydrates, providing examples of minerals like spinel and dolomite that use the same notation but may not represent non-covalently associated entities.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of the dot notation, with some agreeing on its association with non-covalent mixtures while others argue for a broader application that includes various mineral compositions. The discussion remains unresolved regarding the definitive meaning of the notation.

Contextual Notes

The discussion highlights the potential ambiguity in the use of dot notation, with limitations related to definitions and the specific contexts in which the notation is applied. There is an acknowledgment of different interpretations based on chemical contexts.

donaldparida
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I have seen many instances of molecular formulas of two or more compounds with a dot between two adjacent molecular formulas like CuSO4.10H20, CaCO3.MgCO3, K2SO4.Al2(SO4)3.24H20 and so on. What does the dot indicate?
 
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That the substance can be thought of as if it was a stoichiometric (that is, in a simple, constant ratio) mixture of other substances. Sometimes they can be separated, sometimes they can't, so there is no deeper meaning.
 
Generally, it refers to substances non-covalently associated together, such as the case of hydrates.
 
Ygggdrasil said:
substances non-covalently associated together

You are right that's what we usually mean when it comes to hydrates, but the same notation is used also for other situations. Sometimes minerals are written in the oxide form (at least that's how it is called in Polish), like spinel being MgO⋅Al2O3. Also dolomite MgCO3⋅CaCO3 is hardly made of non-covalently associated entities.
 
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