Lesser Invocation; 4th; Blast Shape
This blast shape invocation allows you to improve your eldritch blast by turning it into an arc of energy that “jumps” from the first target to others. An eldritch chain can jump to one or more secondary targets within 30 feet of the first target, allowing you to make additional ranged touch attacks and deal damage to the secondary targets if you hit.
You can “jump” the chain to one secondary target per five caster levels, so you can strike two additional targets at 10th level, three additional targets at 15th level, and four additional targets at 20th level. Each new target must be within 30 feet of the previous one, and you can’t target the same creature more than once with the eldritch chain. If you miss any target in the chain, the eldritch chain attack ends there.
Each target struck after the first takes half the damage dealt to the first target. This reduction in damage to secondary targets applies to any effect that increases the damage of your eldritch blast (such as vitriolic blast). You must make a separate spell penetration check for each target, if applicable.
Source: Complete Arcane