In LeafGreen Pikachu learns Thunder at level 41.
Raichu will not learn thunder.... but pikachu can learn it at level 45
he wont learn it because when u evolve pikachu raichu cant learn moves by itself so just teach him thunder with a TM ok Zeke out
Pikachu learn electro ball at level 18
Pikachu learns thunderbolt at level 26.
Pikachu learns slam at level 21.