Dot and Cross Diagram

Ignore the "transfer of an electron because it's latter on, about Ionic bonding

Dot and Cross diagram helps us to show the electron's configuration and shows the outer shells only. In this case, the Lithium will only show 1 cross in its outer shell and fluorine will have 7 dots in the outer shell.

It is called as the dot and cross diagram because they literally use the dot and cross to symbolize each electrons. Based on the picture above, the cross electron for is lithium and the dot electron is for fluorine.

Dot and cross is a simple symbol to draw, just to differentiate the electron, so we'll know which electron is it from, after the bonding has occur and done.