If li loses an electron to another atom, why is it written li^+1 (with a +1)

The +1 in the superscript indicates that each particle carries a charge of .

Explanation:

Both electrons and protons carry electrical charge. However, the charge on electrons is negative, while the charge on protons is positive. Like all other atoms, a lithium atom contains an equal number of electrons and proton. The charge on protons and electrons balance each other. As a result, lithium atoms are neutral (hence no superscript.)

However, when a lithium atom loses an electron, it will contain more protons than electrons. There won't be enough negative charge to balance the positive charge. This particle will become an ion with a positive charge (a cation.) The number 1 in the superscript +1 indicates the size of this charge.

yes the answer is total mass in unchanged   : )