En física hablamos del átomo, y en química vemos ejemplos en el laboratorio.

Because de + el contracts to del in Spanish.

• de el átomo → del átomo

This is a standard contraction, just like:

• a + el → al

So hablamos del átomo means we talk about the atom.
One important exception: the contraction does not happen if El is part of a proper name, such as El Escorial.

The verb hablar is very often followed by de when it means to talk about.

So:

• hablar de algo = to talk about something

That is why hablamos del átomo is natural.

You may also sometimes see hablar sobre, which can also mean to talk about, but hablar de is extremely common and very natural in everyday Spanish.

Here en means in.

It is used in two slightly different ways in this sentence:

• en física / en química = in physics / in chemistry
  Here it refers to the subject or area.
• en el laboratorio = in the laboratory
  Here it refers to a physical place.

So the same preposition en can introduce both a field of study and a location.

In Spanish, names of school subjects and academic disciplines are normally written in lowercase, unless they begin a sentence.

So Spanish writes:

• física
• química
• historia
• matemáticas

This is different from English, where learners sometimes expect capitals more often.

When Spanish talks about a subject area in a general way, it often uses no article after en.

So:

• en física
• en química

is the normal way to say in physics and in chemistry here.

If you said en la física or en la química, it would usually sound more specific, abstract, or less natural in this classroom-type context.

Spanish often leaves out subject pronouns because the verb ending already shows who is doing the action.

Here:

• hablamos = we talk
• vemos = we see

The -amos and -emos endings tell you the subject is we, so nosotros is unnecessary unless you want emphasis or contrast.

For example:

• Nosotros hablamos del átomo, pero ellos estudian otra cosa.

There, nosotros is used for emphasis or contrast.

Because ver and mirar are not exactly the same.

• ver = to see
• mirar = to look at

In this sentence, vemos ejemplos means something like we see / we come across examples. That sounds natural.

Miramos ejemplos would sound more like we look at examples, which is possible in some contexts, but vemos ejemplos is more natural for the general idea here.

Because ejemplos is being used in a general, non-specific way.

• vemos ejemplos = we see examples

This means examples in general, not a particular set already identified.

If you said vemos los ejemplos, it would mean we see the examples, referring to specific examples that both speaker and listener already know about.

The accent marks show where the stress falls.

• física → stress on the first syllable: FÍ-si-ca
• química → stress on the first syllable: QUÍ-mi-ca
• átomo → stress on the first syllable: Á-to-mo

Without the written accents, Spanish stress rules would suggest a different pronunciation, so the accents are necessary.

They are not optional: they are part of the correct spelling.

The present tense is being used to describe something general, habitual, or typical.

So the sentence gives a general idea like:

• In physics we talk about the atom, and in chemistry we see examples in the lab.

It is not necessarily happening right this second. Spanish, like English, often uses the present tense for routines, facts, and what usually happens in class or in a subject.

Because each part needs its own prepositional phrase:

• en física
• en química
• en el laboratorio

Spanish normally repeats the preposition when each phrase has its own role in the sentence. Leaving it out would sound incomplete or awkward.

So this structure is very natural:

• En física hablamos del átomo, y en química vemos ejemplos en el laboratorio.

Normally y means and, but it changes to e before words that begin with an i sound.

For example:

• padre e hijo
• España e Italia

But here the next word is en, which does not begin with an i sound, so Spanish keeps y:

• ..., y en química...

So y is correct here.