100 points! formation of an ion

aluminum is one of the most common elements in earth's crust, yet it is never found as a pure element in nature. that is, aluminum atoms are always combined with atoms of other elements, such as oxygen. an aluminum oxide compound you will recognize by its name is the gemstone called "ruby". its chemical formula is

al2o3

if every oxygen ion (combined with an aluminum ion) has a charge of -2, what must the charge of each aluminum ion be? how can you tell this? also, what has to happen to an uncharged aluminum atom so that it will bond with oxygen?

disclaimer: if the question is not answered fully or if it makes no sense it will be reported

What you have to realize is who is creating the charge and who is receiving it.

Oxygen and Aluminum  are in their ionic form. Ions are produced by electron movement.

Aluminum gives away electrons (3 of them).

Oxygen takes on electrons (2 of them).

The 2 and the 3 in Al2O3 tells you how many electrons were given up and how they were taken on.

The 2 and the 3 in Al2O3 also tells you (indirectly) what the lowest common denominator is.

So once you understand the above 2 sentences you will understand the answer to your questions.

The lowest common multiple of 3 and 2 is six.

If the Aluminum gives up 3 electrons per atom, then to get to 6, you will have to have two aluminums.

If oxygen takes on 2 electrons then to get to six. There must be 3 oxygens present. Look at the formula

Al2 there are two aluminums

O3 there are three oxygens. That's why the formula is written the way it is.

Aluminum is never seen alone because it is very eager to give up it's 3 electrons. It will combine with almost anything that is willing to receive those electrons.

Compare it to gold. Gold will combine with almost nothing ionically. Separating gold from a none metal won't happen normally, and refining to get rid of that problem just won't occur.  

answer: the enthalpy of the overall chemical reaction is +87.88 kj or +88 kj.

according to hess's law, the overall enthalpy of a reaction is the difference between the sum of enthalpy values of all the products and the sum of enthalpy values of all the reactants.

δh(reaction) = ∑nδh(products) - ∑nδh(reactants)

δh(reaction) = [δh +δh] - [δh]

δh(reaction) = [1(-287.02) + 1(0) ] - [1(-374.9)] kj = +87.88 kj

here, δh (pcl3) = -287.02 kj, δh(cl2) = 0, δh(pcl5) = -374.9 kj

therefore, enthalpy of the overall reaction is +87.88 kj or +88 kj.