reason of the trend
Towards the left of the table, valence shells are less than half full, so these atoms (metals) tend
to lose electrons and have low electronegativity. Towards the right of the table,
valence shells are more than half full, so these atoms (nonmetals) tend to gain electrons and
have high electronegativity. Down a group, the number of energy levels (n) increases, and so does the distance between
the nucleus and the outermost orbital. The increased distance and the increased
shielding weaken the nuclear attraction, and so an atom can’t attract electrons as strongly