So polyatomic ions are several atoms covalently bonded to one another but having a positive or negative charge because the total number of valence electrons from the atoms cannot produce a stable structure. with one or more electrons added or removed, a stable structure results.
example: nitrate
knowing this, why do compounds need to be neutral while polyatomic ions not. why don't compounds follow the same strategy as polyatomic ions such that they add or remove electrons to make themselves stable?

- aluminum and copper chloride.

- the chloride ion to separate the aluminum from the oxygen so that the aluminum can react with the copper ions (and the water molecules).

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.