Trends of electron affinity Trends for electron affinity going across the group increases negatively.
Does this mean Noble gases' electron negativity is more negative than halogens?
I'm confuse here.
Noble gases should have a positive electron affinity as adding an electron would make it unstable and thus, will not form.
But for halogens, their attraction for that 1 electron to fill up the $\mathrm{p}$ subshell is very strong.
But according to the theory that electron affinity increase negatively across the period, does this theory has an exception of noble gases?
Next, what about $\ce{Be}$ and $\ce{Mg}$? Their electron affinities are not negative.
Not exceptions, but see, theories say that going $L→R$ electron affinity increases up to halogens.
For the noble gases, $\Delta_\mathrm{eg}H$ is positive (energy required). While electron affinity is $0$. Which implies no tendency to lose electrons.
For $\ce{Be}$, the small size and nuclear charge are responsible, which is related to $\ce{Mg}$ due to a diagonal relationship.