# Trends of electron affinity

The trend in electron affinity is to increase negatively across a group.

Does this mean noble gases' electronegativity is more negative than halogens?

Noble gases should have a positive electron affinity as adding an electron would make it unstable and thus will not happen.

But for halogens the attraction for that one electron to fill up the $$\mathrm{p}$$ subshell is very strong.

But given the theory that electron affinity increases negatively across the period, does this theory make an exception for 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.