What exactly does the "per mole" unit of heat of atomization mean?

I am facing a confusion in the definition of the standard enthalpy of atomization. The confusion arises because of the "per mole" in its units ($\pu{kJ mol^-1}$).


**My question**: When I say "per mole", do I mean "per mole" of the *product* or per mole of the *reactant*?


When I mean **"per mole" of the product**, my representative reaction for $\Delta H\_\mathrm{a}^\circ$ is:


$$\ce{1/4 P4(s) -> P (g)}$$


And when I mean **"per mole" of the reactant**, my representative reaction for $\Delta H\_\mathrm{a}^\circ$ is:


$$\ce{P4 (s) -> 4P (g)}$$


Using either of them leads to different calculations involving Hess's law or other chemical reactions, hence I feel there is a need to resolve this confusion.




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To add to this confusion, NCERT Chemistry (Part 1 page 171) writes:



> 
> It is the enthalpy change on breaking **one mole of bonds** completely to obtain atoms in the gas phase.
> 
> 
> 


but then gives a representative reaction as:


$$\ce{CH4 -> C(g) + 4H(g)}$$


which involves breaking **4 moles** of bonds instead. 




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If someone could write the correct definition of the standard enthalpy of atomization, with more than one reputed reference to back their claim, it'd definitely resolve this confusion.




According to [Wikipedia](https://en.wikipedia.org/wiki/Enthalpy_of_atomization),



> 
> Standard enthalpy of atomization is the enthalpy change when $1$ mole of gaseous atoms is formed from its element in its defined physical state under standard conditions $(\pu{298.15K}, \pu{1 bar})$.
> 
> 
> 


$\Delta H\_{\text{at}}^{\circ}$ focuses on the production of $1$ mole of atoms from the element. Hence it's defined for the reaction: 


$\ce{\dfrac{1}{8}S8 ->S}$ 


but not for the reaction: 


$\ce{S8 -> 8S}$


So whenever you see the term "per mole", it is, by definition, implicitly referring to the product and not to the reactant. 


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