3.1.3—The trends in electronegativity across

Across a period, electronegativity generally increases from left to right. Nuclear charge increases while the added electrons enter the same principal shell, so shielding changes relatively little; the stronger nuclear attraction and generally smaller atomic radius pull bonding electrons more strongly.

Down a group, electronegativity generally decreases. Although nuclear charge increases, new occupied shells increase atomic radius and inner-shell shielding, so the bonding electron pair is farther from the nucleus and feels a weaker effective attraction.

Explain a trend by linking direction to the three factors: nuclear charge, distance/atomic radius and shielding. State the overall trend first, then identify which factor strengthens or weakens attraction and why the dominant effect gives the observed direction.

Use ‘generally’ rather than claiming a perfectly smooth rule for every comparison. Do not reverse the down-group direction, explain the trend with proton number alone, or use bond-polarity classification before the neighbouring application objective.