To find the total amount of salt Kenji put into the soup, we need to add the initial amount of salt he mixed in with the additional amount of salt he added later.
Initial amount of salt: 5 grams
Additional amount of salt: 0.5 grams
Now, adding these two amounts together:
\[ 5 \text{ grams} + 0.5 \text{ grams} = 5.5 \text{ grams} \]
Therefore, Kenji put a total of 5.5 grams of salt into the soup.