Why Lewis theory falls short:
* Electron transfer, not sharing: Ionic compounds form by the complete transfer of electrons from a metal (cations) to a non-metal (anions). Lewis structures focus on sharing electrons, which doesn't accurately represent the nature of ionic bonding.
* Electrostatic attraction: The primary force holding ionic compounds together is the electrostatic attraction between oppositely charged ions. Lewis structures don't explicitly depict this attraction.
* Lattice structure: Ionic compounds exist in a 3D crystal lattice, not as individual molecules as depicted in Lewis structures.
How to determine ionic compound formulas:
1. Identify the ions: Determine the charges of the cation and anion involved. This is usually done by referencing the periodic table and knowing common polyatomic ions.
2. Balance the charges: The formula of an ionic compound must be electrically neutral. Use subscripts to indicate the number of each ion required to achieve this neutrality.
3. Example: Sodium (Na+) and chloride (Cl-) form sodium chloride (NaCl). One sodium ion with +1 charge balances one chloride ion with -1 charge.
In summary: While Lewis theory is valuable for understanding covalent bonds, it's not the right tool for determining ionic compound formulas. Understanding ion charges and balancing charges is crucial for predicting the composition of ionic compounds.
