Why the formation of ionic compounds (like NaCl) is thermodynamically favoured?
Answers
Answer:
the resulting ionic compound is more stable than the ions that formed it. The extra energy from the ions is released as heat when ionic bonds form. When more heat is released from a reaction than is needed for it to happen, the reaction is exothermic.
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Answer:
Ionic bonds form between two atoms with a large electronegativity difference between each other. Typically, this is a reaction between metals and nonmetals. The atoms are so reactive because they do not have complete valence electron shells. In this type of bond, an electron from one atom is essentially donated to the other atom to fill its valence electron shell. The atom that "loses" its electron in the bond becomes more stable because donating the electron results in either a filled or half-filled valence shell. The initial instability is so great for the alkali metals and alkaline earths that little energy is required to remove the outer electron (or 2, for the alkaline earths) to form cations. The halogens, on the other hand, readily accept the electrons to form anions. While the anions are more stable than the atoms, it's even better if the two types of elements can get together to solve their energy problem. This is where ionic bonding occurs.
To really understand what's going on, consider the formation of sodium chloride (table salt) from sodium and chlorine. If you take sodium metal and chlorine gas, salt forms in a spectacularly exothermic reaction (as in, don't try this at home). The balanced ionic chemical equation is:
2 Na (s) + Cl2 (g) → 2 NaCl (s)