How to know that a bond is ionic or covelent by just looking at it ?

Ionic bonds are made up of a metal and a nonmetal elements while covalent bonds are are made up of two metal. So, you can just look at the periodic table and identify which compounds have two metals and which have one metal and one nonmetal. Also, those compounds with high electronegativity difference are very likely to be ionic while the opposite is covalent. HOWEVER, some compounds can be both covalent and ionic. For instance, if HCI gas is at higher temperatures, then it is ionic while it would be covalent at room temp. 

Hope I've helped. 

            - Dotz

Okay well gravitational energy is matter forced by gravity making energy though the kinetic energy then the electric energy produces electricity from the kinetic energy and the kinetic energy gets its energy from the gravitational energy. was that the answer you wanted or something else?