Scoring piano chords

In scoring a piano chord, suppose I put in a C chord (C-E-G-C) in the treble (or bass) clef and I want the top note of the chord to be held for all four beats of the measure, but I want the bottom three notes (C-E-G) to drop off after the first beat since I will be writing an arpeggio with the bottom three notes on beats 2, 3 and 4 while while wanting the top note to be held. If I write the chord with dotted half notes and then go back and try to convert the bottom notes to quarter notes, the entire chord changes to quarter notes. What I want is for the bottom notes to be "black notes" and the top C to be a half note. How do I make that happen?