Ao chegar em casa, percebi que o celular estava no sofá.

It is a very common Portuguese structure meaning upon arriving home or when I arrived home.

• ao = a + o
• chegar = to arrive

In this pattern, ao + infinitive often means when/upon doing something.

So:

• Ao chegar em casa = When I got home / Upon arriving home

This is a more compact, slightly more formal way to say:

• Quando cheguei em casa

Because after ao in this structure, Portuguese uses the infinitive, not a conjugated verb.

So you get:

• ao chegar = upon arriving
• ao sair = upon leaving
• ao entrar = upon entering

If you use a fully conjugated verb, you would switch to a different structure, such as:

• Quando cheguei em casa...

So:

• Ao chegar em casa... = infinitive structure
• Quando cheguei em casa... = conjugated clause

The subject is understood from the main clause: eu.

In Portuguese, the subject is often omitted when it is clear from context. In this sentence:

• percebi = I noticed / I realized

Since percebi clearly shows first person singular, we understand that the person who arrived home is also I.

So the sentence naturally means:

• When I got home, I noticed that...

Portuguese often avoids repeating eu unless there is emphasis or contrast.

Because chegar em casa is the normal Brazilian Portuguese way to say arrive/get home.

Here, em casa refers to the destination reached as a location: at home / home.

Compare:

• Vou para casa. = I’m going home.
• Cheguei em casa. = I arrived home / I got home.

So:

• para casa is common with movement toward home
• em casa is common with being/arriving at home

In Brazil, chegar em is very common in everyday speech.

Because Ao chegar em casa is an introductory adverbial phrase. It sets the time or circumstance for the main action.

So the sentence is divided like this:

• Ao chegar em casa, = time/circumstance
• percebi que o celular estava no sofá. = main clause

The comma helps mark that break, much like in English:

• When I got home, I noticed...

Both can work, but they are not always identical.

• perceber often means to realize, to notice, to become aware
• notar often means to notice, especially by observation

In this sentence, percebi sounds very natural if the speaker suddenly became aware of the phone’s location.

• Percebi que o celular estava no sofá. = I realized/noticed the phone was on the couch.
• Notei que o celular estava no sofá. = I noticed the phone was on the couch.

Percebi can sometimes suggest a small moment of recognition, while notei can sound a bit more like direct observation.

Estava is the imperfect past of estar, and it fits the context because the whole sentence is in the past.

• percebi = I noticed
• at that moment in the past, the phone was on the couch
• so: estava no sofá

Compare:

• está no sofá = is on the couch now
• estava no sofá = was on the couch then

As for ficava, that usually means something more like was located or used to be, depending on context. It would sound less natural here.

• O celular estava no sofá. = The phone was on the couch.
• O celular ficava no sofá. = The phone used to stay on the couch / was located on the couch, which is odd in this situation.

No is a contraction:

• em + o = no

So:

• no sofá = on the sofa/couch

Portuguese often contracts prepositions with articles:

• em + o = no
• em + a = na
• de + o = do
• de + a = da

So this sentence contains:

• o celular = the cellphone
• no sofá = on the couch

Portuguese uses definite articles much more often than English does.

So o celular literally means the cellphone, but in natural English we might just say my phone or the phone, depending on context.

In Portuguese, it is very normal to say:

• o celular
• a chave
• o carro

even when English might use a possessive or omit the article in a different way.

In context, o celular probably refers to a specific phone already understood to be the speaker’s.

Yes, absolutely. That is very natural and probably more straightforward for a learner.

Compare:

• Ao chegar em casa, percebi que o celular estava no sofá.
• Quando cheguei em casa, percebi que o celular estava no sofá.

The meaning is basically the same.

The difference is mostly stylistic:

• ao + infinitive = a little more compact, slightly more polished or formal
• quando + past verb = more explicit and very common in everyday speech

Both are correct in Brazilian Portuguese.

Because perceber que... means to realize/notice that...

This is a very common structure:

• Percebi que ele saiu. = I realized that he left.
• Percebi que estava tarde. = I realized that it was late.
• Percebi que o celular estava no sofá. = I noticed that the phone was on the couch.

So que introduces the content of what was realized or noticed.

Yes, celular is the usual word in Brazil for cell phone/mobile phone.

In European Portuguese, people more often say:

• telemóvel

So:

• Brazil: celular
• Portugal: telemóvel

If you are learning Brazilian Portuguese, celular is exactly the right word.

Yes. Sofá can be translated as sofa or couch.

In everyday English, either translation works here:

• The phone was on the sofa
• The phone was on the couch

The Portuguese word is very straightforward in this case.

The original sentence is already natural, but in casual speech many Brazilians might say something like:

• Quando cheguei em casa, percebi que o celular tava no sofá.

Changes:

• Ao chegar em casa → Quando cheguei em casa sounds more conversational
• estava → tava is a very common spoken reduction of estava

So the original sentence is correct and natural, but a spoken version may sound a bit more relaxed.