Thank you for your question! I have moved it into its own thread so that other users can find it more easily.
Deciding when to use a definite article can definitely be tricky for English speakers learning Spanish! You'll get a feel for it eventually, but it might take a little time for it to become automatic when you're speaking. This forum thread
contains a full explanation about how the definite article works in Spanish.
The gist of that thread is that you use a definite article in two general instances:
- when you want to talk about specific things
- e.g. If you say Quiero un pedazo del pan "(I) want a piece of the bread," you mean "I want a piece of the bread (that we're talking about/that is right here)." If you just said Quiero un pedazo de pan "I want a piece of bread," without the article, you could be talking about any bread at all. Pan is just describing pedazo.
- when you are talking about something as a concept or as a whole
- e.g. If you want to talk about the concept of loyalty, you'll use the definite article and say la lealtad: La lealtad es importante "Loyalty is important."
(If this is too concise/difficult to follow, be sure to have a read of the full explanation in the thread I linked above.)
Now that we've got the general rules down, let's take a look at the phrases you've provided.
1. La oportunidad de ir al Caribe por una semana de sol y diversión.
Here, the article isn't used: una semana de sol y diversión.
This is actually just like the example of un pedazo de pan
"a piece of bread" that we looked at above. In this phrase, we aren't pinpointing specific things or looking at whole concepts; instead, sol
"sun" and diversión
"fun" are just being used to describe semana
"week." What kind of week is it? A week of fun and sun.
It might be easier to look at this as its own rule: No article is required when nouns following de
"of" are just descriptive.
2. Llegamos a San Juan. El sol, el calor y la arena nos saludaron.
Here, the definite article is used: el sol, el calor y la arena
. This is because we're talking about entire concepts: the concept of sun (el sol
), the concept of heat (el calor
), and the concept of sand (la arena
). It's just like talking about the concept of loyalty, where we have to use la lealtad.
I hope that this is helpful! Do let me know if you still have any questions.