What is the proper structure for 3-methylpentane? draw the molecule on the canvas by choosing buttons from the tools (for bonds), atoms, and advanced template toolbars. the single bond is active by default?

Below is the structure of 3-Methylpentane. The word pentane in name specifies the parent chain which ends on -ane (alkane) and pent- shows number of carbon atoms is parent chain (pent=5). The position of substituent is specified at the start i.e. 3. 

The mass has escaped into a gas which you can not see so the law stays true.