wǒ děng le zhěnggè xiàwǔ.

Here 了 is the perfective aspect particle. It shows that the action of waiting is viewed as a completed event.

So the sentence is not just about the verb 等 meaning to wait. It is specifically saying that the waiting happened as a finished action: I waited the whole afternoon.

A helpful point for English speakers: 了 does not simply equal the English past tense. It marks completion or boundedness, not just past time. In this sentence, though, the meaning naturally comes out as past.

Because this 了 is attached to the verb. The basic pattern here is:

Verb + 了 + duration

So:

等了整个下午 = waited for the whole afternoon

Mandarin often puts a duration expression after the verb when saying how long an action lasted.

If you put 了 at the very end, that is usually a different 了: the sentence-final 了, which often adds a sense of a new situation or current relevance.

Compare:

• 我等了整个下午。 = I waited the whole afternoon.
• 我等了整个下午了。 = I’ve waited all afternoon already / I’ve been waiting all afternoon.

That second sentence has a stronger feeling that this matters now.

整个下午 means the whole afternoon or the entire afternoon.

The word 整个 means whole or entire. The 个 here is the very common general classifier. In many expressions, 整个 + noun is the normal way to say the whole + noun.

So:

• 整个下午 = the whole afternoon
• 整个星期 = the whole week
• 整个城市 = the whole city

For an English speaker, it may feel odd that a classifier appears inside something that means whole, but in Mandarin this is very natural.

No. In this sentence, 整个下午 is not the thing being waited for. It tells you how long the waiting lasted.

So grammatically, it works as a duration expression.

That means the structure is basically:

我 + 等 + 了 + 整个下午
I + wait + completed + the whole afternoon

The thing or person being waited for is simply not stated.

Yes. Very often, Mandarin leaves out information that is already clear from context.

So 我等了整个下午 can naturally mean:

• I waited the whole afternoon.
• I waited for him/her/them the whole afternoon.
• I waited for it the whole afternoon.

If you want to say the object explicitly, you can add it:

• 我等了他整个下午。 = I waited for him the whole afternoon.

Mandarin frequently omits objects when they are understood, and this is one reason sentences can look shorter than their English translations.

Yes. All of these are natural, but they feel slightly different:

• 我等了整个下午。 = I waited the whole afternoon.
  This stresses the entire afternoon.

• 我等了一个下午。 = I waited for an afternoon / I waited all afternoon.
  This focuses more on the length of time.

• 我等了一下午。 = I waited all afternoon.
  This is very common in everyday speech and sounds a bit more casual.

You may also hear:

• 我等了一整个下午。

That adds even more emphasis to the idea of the entire afternoon.

Because this sentence is expressing duration, not just when something happened.

In Mandarin, a phrase placed before the verb often tells you when an action happened:

• 我下午等他。 = I waited for him in the afternoon.

But a phrase placed after the verb often tells you how long the action lasted:

• 我等了整个下午。 = I waited the whole afternoon.

This is a very common pattern:

• 我学了两年中文。 = I studied Chinese for two years.
• 他睡了十个小时。 = He slept for ten hours.

So after the verb, it often answers for how long?

In this sentence, it most naturally refers to a specific afternoon, understood from context, and the English meaning is usually just the whole afternoon or all afternoon.

It does not usually mean every afternoon. If you want that meaning, Mandarin would normally make it explicit:

• 我每天下午都等他。 = I wait for him every afternoon.

So in 我等了整个下午, the listener normally understands one particular afternoon, not a repeated habit.

Usually you use 没 for this kind of completed action, and the verb 了 normally disappears:

• 我没等整个下午。

That can mean I didn’t wait the whole afternoon.

Be careful: in English, that could mean either:

1. I did not wait at all.
2. I waited, but not for the entire afternoon.

Mandarin can have the same ambiguity unless you add more context.

If you want to say clearly that you didn’t wait at all all afternoon, you could say something like:

• 我整个下午都没等。

If you want to say you only waited for part of the afternoon, you could say:

• 我没等整个下午，只等了两个小时。 = I didn’t wait the whole afternoon; I only waited two hours.

Yes. It is a very useful pattern:

Subject + Verb + 了 + duration

Examples:

• 我等了整个下午。 = I waited the whole afternoon.
• 他工作了三天。 = He worked for three days.
• 我们聊了两个小时。 = We chatted for two hours.

This is one of the most important ways Mandarin expresses how long an action lasted. If you remember this pattern, you can build many similar sentences very easily.