Learn Hardcore Spanish (Spain): Al llegar a mi dormitorio, dejo el móvil en la mesa. - When I arrive in my bedroom, I leave my phone on the table.

So al llegar a mi dormitorio ≈ “when I arrive at my bedroom”, but with a slight nuance of “as soon as / upon arriving”, emphasizing that the action that follows happens immediately afterward.

You could also say:

Cuando llego a mi dormitorio, dejo el móvil en la mesa.

That’s perfectly correct. Al llegar is a bit more compact and often feels slightly more formal or written than cuando llego.

Why is llegar in the infinitive (llegar) and not conjugated (llego) in al llegar?

In the structure al + infinitive, the verb must stay in the infinitive:

al llegar
al entrar
al terminar

The subject of that infinitive is usually the same as the subject of the main verb:

Al llegar a mi dormitorio, dejo el móvil…
→ Subject of llegar and dejo is yo (I).

Spanish understands “I” as the subject of both actions without needing to repeat it. So you don’t conjugate llegar there; you leave it in the infinitive because the al + infinitive construction demands it.

Why is it a mi dormitorio and not en mi dormitorio after llegar?

With llegar (to arrive), Spanish normally uses the preposition a to express the destination:

llegar a casa – to arrive home
llegar a Madrid – to arrive in Madrid
llegar a mi dormitorio – to arrive at my bedroom

A expresses direction/goal.

En is for location (being in/at a place), not for the destination of arriving:

Estoy en mi dormitorio. – I am in my bedroom.
Llego a mi dormitorio. – I arrive at my bedroom.

So llegar en mi dormitorio would be incorrect in this sense.

Could I say Cuando llego a mi dormitorio instead of Al llegar a mi dormitorio? Is there a difference?

Yes, you can say:

Cuando llego a mi dormitorio, dejo el móvil en la mesa.

This is fully correct and very natural.

Difference in feel:

Cuando llego… – neutral “when I arrive…”
Al llegar… – “upon arriving…”; slightly more compact, and in many contexts a bit more formal or “written style,” though it’s also used in speech.

In everyday conversation, both are fine. The meaning here is essentially the same: a habitual sequence of actions.

Why is it mi dormitorio and not el dormitorio?

Spanish uses possessive adjectives (mi, tu, su, nuestro, etc.) in a similar way to English my, your, his/her when the possession is important or not obvious from context.

mi dormitorio – my bedroom
el dormitorio – the bedroom (could be any/basically “the bedroom” in general)

In this sentence, you’re clearly talking about your own routine in your space, so mi dormitorio makes sense.

You could say al llegar al dormitorio if, for example, in a story everyone already knows which specific bedroom you’re talking about, but mi dormitorio is more natural if you mean your personal room.

What exactly does dejo mean here? Why dejo el móvil and not pongo el móvil?

The verb dejar has several meanings; two common ones are:

to leave (something somewhere)
to leave / let / allow (e.g. my parents let me go out = mis padres me dejan salir)

Here it’s meaning 1:
dejar el móvil en la mesa = to leave / put down the phone on the table and not take it with you.

Poner means to put / place something somewhere, without the idea of leaving it behind:

Pongo el móvil en la mesa. – I put the phone on the table.
Dejo el móvil en la mesa. – I leave the phone on the table (and it stays there).

Both can work, but dejar is very natural when you’re describing a habitual place where you always leave something (keys, phone, wallet, etc.).

Why is it el móvil and not mi móvil? Is that normal in Spanish?

Both are possible:

Dejo mi móvil en la mesa. – I leave my phone on the table.
Dejo el móvil en la mesa. – I leave the phone on the table.

In context, el móvil will almost always be understood as your own phone, especially in a sentence about your personal routine. Spanish often uses the definite article (el/la) instead of a possessive when it’s obvious whose thing it is from context.

Also, in Spain:

el móvil is the standard word for mobile phone / cell phone.
(In much of Latin America, you’ll hear el celular instead.)

So dejo el móvil… is very idiomatic Peninsular Spanish.

Why is it en la mesa and not sobre la mesa? Is there a difference?

Both en la mesa and sobre la mesa can mean “on the table”.

en la mesa – very common, can mean on the table or at the table, depending on context.
sobre la mesa – literally “on (top of) the table”, a bit more explicit about the object being on the surface.

In everyday speech, en la mesa is extremely frequent, even when the object is clearly on top of the table. So:

Dejo el móvil en la mesa. – Totally natural.
Dejo el móvil sobre la mesa. – Also correct; may sound a touch more precise or formal.

Here, en la mesa is the most typical choice.

Why is the verb dejo in the present tense? Does it mean I do it right now or as a habit?

Spanish simple present (dejo) can express:

Habitual actions (things you usually/always do)
- Todos los días dejo el móvil en la mesa. – Every day I leave my phone on the table.
General truths / routines
- Al llegar a mi dormitorio, dejo el móvil en la mesa. – Whenever I arrive in my bedroom, I leave my phone on the table.

So in this sentence, dejo describes a habitual routine, not a single action right now.

If you wanted to talk about a specific past time, you’d use the past:

Al llegar a mi dormitorio, dejé el móvil en la mesa. – When I arrived at my bedroom, I left my phone on the table. (one specific event)

Could the word order change, like Dejo en la mesa el móvil or El móvil lo dejo en la mesa?

Yes, Spanish word order is flexible, especially with objects:

Dejo el móvil en la mesa. – neutral, most typical order.
Dejo en la mesa el móvil. – also correct; slight emphasis on el móvil at the end.
El móvil lo dejo en la mesa. – very natural colloquial order to emphasize el móvil (“The phone, I leave it on the table”).

El móvil lo dejo… uses lo (direct object pronoun) for emphasis or clarity, a kind of topicalization:
El móvil, what do I do with it? Lo dejo en la mesa.

All of these can be correct; the original sentence just uses the most straightforward, neutral word order.

Why are some nouns masculine (el móvil, mi dormitorio) and others feminine (la mesa)?

In Spanish, all nouns have grammatical gender, masculine or feminine, and this affects the articles and adjectives:

el móvil – masculine
mi dormitorio – masculine
la mesa – feminine

Some rough patterns:

Nouns ending in -o are usually masculine: el dormitorio.
Nouns ending in -a are usually feminine: la mesa.
Nouns ending in consonants, like móvil, have to be memorized; móvil is masculine (el móvil).

The important part is that articles and adjectives must agree in gender and number:

el móvil (masc. sing.)
mi dormitorio (masc. sing.)
la mesa (fem. sing.)

So the sentence is consistent: el móvil (masc.), mi dormitorio (masc.), la mesa (fem.).