# Electrical fields, ions

1. Oct 15, 2006

### glid02

Here is the question:

A uniform electric field of magnitude 604 N/C exists between two parallel plates that are 3.66 cm apart. A proton is released from the positive plate at the same instant that an electron is released from the negative plate. Determine the distance from the positive plate at which the two pass each other. (Ignore the electrical attraction between the proton and electron.)

Repeat the calculation for a sodium ion (Na+) and a chlorine ion (Cl-).

I found part 1 using qE/2m*t^2 = xf, plugging in both charges and their masses and solving for t^2 then plugging that back into qE/2m*t^2 for the proton.

My question is how to find the charge and masses of the sodium and chlorine ions. My best guess is to use their atomic weight and subtract the weight of one proton or one electron, and for their charge use the charge of one proton or one electron. Can anyone back me up on this?

Thanks a lot,
Gregg

2. Oct 15, 2006

### drpizza

Atoms don't become ions by gaining or losing a proton. The sodium ion has a positive charge because it loses an electron. The chlorine ion has a negative charge because it gains an electron.

3. Oct 15, 2006

### Andrew Mason

I can't follow what you are doing in the first part to comment. I would create an expression for relative separation and determine where that = 0.

As for your 'guess', just use their molar weight divided by avogradro's number. The ion is just missing an electron (not a proton) and the difference due to the missing electron's weight is negligible.

AM