Atomic bonding and Molecular Structure : How and why atoms combine • When atomic-sized particles combine, they release energy and become more stable. • When a bond between atomic sized particles is broken, they absorb energy and become less stable. Temperature change can indicate what is happening at the atomic level. • When the temperature increases: Bond formation > Bond breaking • When the temperature/energy decreases: Bond breaking > Bond formation Ionic bonding (involves the transfer of electrons, and thus involves the IE of one atom and the EA of another atom) E.g. formation of NaCl: Na to Na + + e- … IE 496 kJ/mol in (endothermic) (+496) Cl + e – to Cl – … EA 349 kJ/mol out (exothermic) (–349) “For any stable compound to form from its elements, there must be a net lowering of the energy. In other words energy must be released.” For NaCl to form spontaneously, the total energy must be a negative value (not +147). Thus, some other factor must contribute to the energy equation. That factor is called lattice energy.
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This note was uploaded on 04/12/2011 for the course CHEM 1010 taught by Professor Marshall during the Spring '11 term at North Texas.