Em cima da cómoda, deixei as chaves e o outro cabide.

Because em cima de is a fixed expression, and de contracts with the feminine singular article a.

So:

• em cima de + a cómoda
• becomes em cima da cómoda

This is very common in Portuguese:

• de + o = do
• de + a = da
• de + os = dos
• de + as = das

So em cima da cómoda means on top of the chest of drawers / dresser.

Yes, but em cima de is usually the more natural everyday choice when you mean something is physically on top of something.

• em cima da cómoda = on top of the dresser
• sobre a cómoda = also possible, but often sounds a bit more formal or less conversational

Also, sobre very often means about / regarding, so learners usually find em cima de safer and more natural for physical location.

Portuguese can move a location phrase to the front for emphasis or to set the scene.

So both of these are natural:

• Em cima da cómoda, deixei as chaves e o outro cabide.
• Deixei as chaves e o outro cabide em cima da cómoda.

The version with Em cima da cómoda first gives a little more focus to the place, almost like saying On top of the dresser, I left...

The comma separates the fronted location phrase from the rest of the sentence.

Here, Em cima da cómoda is an introductory phrase. In Portuguese, it is very common to put a comma after that kind of opening element, especially when you want the sentence to sound clear and well-structured.

So the comma is not changing the meaning; it is mainly helping the rhythm and organization of the sentence.

Deixei is the 1st person singular preterite of deixar.

That means:

• eu deixei = I left / I put down
• it refers to a completed action in the past

So the speaker is talking about one finished action: they left or put the items there.

Because Portuguese often drops subject pronouns when the verb ending already makes the subject clear.

Here, deixei already shows that the subject is I.

So:

• deixei = I left
• eu deixei = also correct, but more emphatic

You would add eu if you wanted contrast or emphasis, for example:

• Eu deixei as chaves, não foi ela.
  I left the keys, not her.

It can mean either, depending on context.

With deixar, Portuguese often focuses on the result: something ended up somewhere.

So in this sentence, deixei could mean:

• I left the keys and the other hanger on top of the dresser
• I put the keys and the other hanger on top of the dresser

If the wider context suggests forgetting them there, left may sound better. If the action was deliberate placement, put may fit better.

O outro cabide means the other hanger.

There are two useful points here:

1. Outro normally comes before the noun in Portuguese.
   So you say outro cabide, not usually cabide outro.

2. The article o makes it specific.

   • o outro cabide = the other hanger
   • outro cabide = another hanger / some other hanger

So o outro cabide suggests that the listener already knows which other hanger is being talked about.

Because Portuguese often uses definite articles with specific nouns where English may or may not do the same.

Here, as chaves means the keys: specific keys that both speaker and listener can identify from context.

Compare:

• as chaves = the keys
• umas chaves = some keys
• chaves without an article is possible in some contexts, but not the most natural choice here

So in this sentence, the article makes the noun sound specific and complete.

Cómoda is a piece of furniture with drawers: a dresser or chest of drawers.

Yes, this spelling is the standard European Portuguese one: cómoda.

A learner may notice that Brazilian Portuguese usually writes this word as cômoda. That spelling difference reflects pronunciation differences between Portugal and Brazil.

So for Portuguese from Portugal, cómoda is exactly what you would expect to see.