[u0625552]

Calculate the de Broglie wavelength of a Helium atom moving at a speed of 196.0 m/s.

So I converted the mass of Helium to kg. Then i us the formula λ = h / mv. Plug in everything 6.626 * 10^-34/(.004 * 196) and got 8.4460 * 10^-34. But when I typed the answer in it says that it was the wrong answer. Can someone tell me what i did wrong? Thanks.

[Arctic-Nation]

You used the mass of one mole of Helium atoms, instead of that of a single atom. Divide the mass you used by Avogadro's number and you'll get there.