When a substance dissolves, it undergoes a

2 types of changes
physical change
chemical change

the easy way to tell the difference is
a physical change is genrally reversable
it changes the look but not the composition
for example, water freezes into ice is physical change

a chemical change is generally not reversable (easily)
ex metal rusting, egg rotting
it changes theh composition itself

when a substance disolves, it actually merges and the molecules move around and sometimes bond
so it's a chemical change

Outermost (valence) electrons