I need to know the predicted and actual electron configuration for Lanthanum

Question

I know for lets say Cr the predicted config is [Ar] 3d44s2 and the actual is [Ar]3d54s1 but lanthanum is different and i don't know how to do it. Any help?

You can find the actual electron configuration here. Click on element #57 and scroll down the menu on the left side of the page to electron configuration.
http://www.webelements.com/

thank you, do you know what the predicted config would be though?

I was thinking 6s2 4f1

Yes, I believe you are right. According to the mnemonic most of us memorize, 6s fills, then 4f, then 4d.