Reaction (or lack thereof) between oxygen and halogen gas I understand that oxygen and halogens are both very electronegative elements and it would makes sense that they don't want to associate with each other at all. However, I know that oxides of halogens ($\ce{Cl2O, ClO2, ClO, Cl2O2}$ etc.) do exist. When reading about halogens, it says that chlorine gas doesn't react with oxygen gas. I tried to find the intuitive reasoning behind this phenomenon online, but to no avail.
I know that chlorine and fluorine gas can react to produce chlorine trifluoride (fluorination of chlorine), proving that two diatomic, covalent and non-polar gases of electronegative elements can react.
$$\ce{Cl2 + 3F2 -&gt; 2ClF3}$$
Also, drawing comparison with the reaction between nitrogen and oxygen gas:
$$\ce{N2 + O2 -&gt; NO}$$
$$\ce{N2 + 2O2 -&gt; NO2}$$
Nitrogen's triple bond is loads stronger than the covalent bonds from oxygen or chlorine, and it can still react with oxygen gas, albeit only under extreme conditions (lightning). Is this the case with chlorine? Even so, it only makes sense that it requires a lower temperature, as the energy needed to atomize them is lower (I haven't done the calculations with enthalpy and entropy yet). I can't find any reference to a reaction such as this online, though.
Most oxides of chlorine can only be made from compounds like chlorites and chlorates or by other novel methods. Is there a reason oxygen and chlorine (or other halogens, but chlorine in particular) can't react with oxygen gas? Is there something stopping them from reacting that I don't know about? Is it due to undesirable entropy changes? Or are the reactions I mentioned special, allowing two relatively nonreactive gases to react?
Your on the right track: in order to form a new compound, old bonds must be broken. This requires energy, even though the reaction may, overall , be exothermic. This is called the activation energy.
Think of it as pushing a car a short distance up one side of a hill before it reaches the peak and then rolls a long distance down the other side.
For example, in the dark, at room temperature, $\ce{Cl2}$ and $\ce{H2}$ coexist quietly in a flask... until light activates the chlorine (wait for the bang).
On the other hand, add enough energy, and even endothermic reactions take place, and, if the product is comparatively stable, or metastable, some can be left afterwards. For example $\ce{O2}$ is fairly stable, but given some energy input, e.g. from an electric discharge or from shortwave ultraviolet radiation, $\ce{O3}$, ozone, is produced, though that reaction is not thermodynamically favorable. The ozone is waiting to decompose... once it's activation energy is achieved.