Learn Hardcore Portuguese (Portugal): Na rádio, falam hoje sobre ciência e tecnologia. - On the radio, today they are talking about science and technology.

a rádio (feminine): the radio medium or a radio station
- na rádio = on the radio / at the radio station
o rádio (masculine): the physical device (the radio set)
- no rádio = in/on the radio (device)

In the sentence “Na rádio, falam hoje…”, we are talking about what is being broadcast, so it uses the feminine form: a rádio → na rádio.

In Brazilian Portuguese, it’s much more common to say no rádio even when you mean “on the radio” (the medium), so this “na rádio” is a clear hint that the sentence is European Portuguese (Portugal).

What exactly does “Na” mean here?

Na is a contraction of the preposition em (in / on / at) and the feminine definite article a (the).

em + a = na
em + o = no

So:

na rádio = em a rádio → in/on the radio
You cannot normally write em a rádio separately; you must contract to na rádio.

Why is there a comma: “Na rádio, falam hoje…”? Is it required?

The comma is there because “Na rádio” is placed at the beginning as a fronted phrase of place (like a topic or setting):

Na rádio, falam hoje… = On the radio, they’re talking today…

In Portuguese, when you move an adverbial phrase (time, place, manner) to the front, it is very common to separate it from the rest of the sentence with a comma.

It’s not absolutely mandatory in all styles, but it’s standard and natural here. You could also say:

Hoje, na rádio, falam sobre ciência e tecnologia.

Why isn’t there a subject pronoun like “eles”? Who is “falam”?

Portuguese is a “pro‑drop” language: subject pronouns (eu, tu, ele, nós, vocês, eles) are often omitted because the verb ending already shows the person and number.

(Eles) falam hoje… → Falam hoje…

So falam here implicitly means “they talk / are talking”.
“Eles” would usually only be added for emphasis or contrast, e.g.:

Eles falam hoje sobre ciência e tecnologia, não nós.
They are the ones talking about science and technology today, not us.

Who does “falam” refer to? Is it a specific “they”?

Grammatically, falam is 3rd person plural, present tense of falar (to talk, to speak).

In context, it normally means:

They (the presenters / journalists / people at the radio station) talk today about…

It can also be understood as a generic “they”, similar to English:

On the radio, they’re talking today about science and technology
→ meaning “people on the radio”, “the radio shows”, etc.

Portuguese can also use this 3rd person plural to mean “people in general”, but here the natural reading is “the people working on the radio station”.

Why is it “falam hoje” and not something like “estão a falar hoje” or “vão falar hoje”?

Portuguese often uses the simple present with a time word like hoje (today) to talk about planned or scheduled events, where in English you might prefer present progressive or “going to”:

Na rádio, falam hoje sobre ciência e tecnologia.
= On the radio, today they’re talking / they’re going to talk about science and technology.

You can say:

Na rádio, estão hoje a falar sobre ciência e tecnologia.
(They are in the process of talking about it today, right now.)
Na rádio, vão falar hoje sobre ciência e tecnologia.
(They will speak / are going to speak about it today.)

But the plain present (falam) is very natural in European Portuguese for a programme schedule or planned topic for today.

Where can “hoje” go in the sentence? Does the position change the meaning?

Hoje is quite flexible. All of these are grammatically correct:

Na rádio, falam hoje sobre ciência e tecnologia.
Na rádio, hoje falam sobre ciência e tecnologia.
Hoje, na rádio, falam sobre ciência e tecnologia.
Falam hoje, na rádio, sobre ciência e tecnologia.

The meaning (time = today) stays the same; the difference is in rhythm and emphasis:

Starting with Hoje, na rádio, … puts more emphasis on “today”.
Starting with Na rádio, … puts more emphasis on the radio as the setting.

In everyday speech, Hoje, na rádio, falam… and Na rádio, hoje falam… are probably the most neutral-sounding.

What does “sobre” mean here? Could you also use “de”?

In this context, sobre means “about / on the subject of”:

falar sobre X = to talk about X
Na rádio, falam hoje sobre ciência e tecnologia.
= On the radio, today they talk about science and technology.

You could also use:

falar de X
→ Na rádio, falam hoje de ciência e tecnologia.

In many cases, falar sobre and falar de are very close in meaning.
Nuances (not strict rules):

falar sobre can sound a bit more neutral/formal or “on the topic of”.
falar de is extremely common and can feel slightly more colloquial.

Another more formal option is:

falar acerca de X = to speak concerning X (quite formal).

Why is it “sobre ciência e tecnologia” without articles? Could it be “sobre a ciência e a tecnologia”?

Both are possible, with a slight nuance:

sobre ciência e tecnologia
- No articles → the fields in a general, unspecific way.
- about science and technology (as general topics)
sobre a ciência e a tecnologia
- With articles → a bit more specific or definite, often suggesting “these domains as we know them”, sometimes sounding slightly more formal.
- about (the subject of) science and (the subject of) technology

In everyday speech, “sobre ciência e tecnologia” is very natural and perfectly correct.

Why are “ciência” and “tecnologia” not capitalised in Portuguese?

Portuguese uses fewer capital letters than English.

Names of fields of study and abstract disciplines (science, technology, history, mathematics, etc.) are written with a lowercase initial, unless they are part of a proper name (e.g. the official name of a course, institution, or event):

ciência, tecnologia, história, matemática
Faculdade de Ciências e Tecnologia da Universidade X (here it’s part of a proper name, so it’s capitalised)

So “ciência e tecnologia” is correctly written with lowercase.

Is there any practical difference between “Na rádio, falam hoje…” and “Hoje, na rádio, falam…”?

They both mean essentially the same thing:

Na rádio, falam hoje sobre ciência e tecnologia.
Hoje, na rádio, falam sobre ciência e tecnologia.

The difference is slight and mostly about information order:

Na rádio, falam hoje…
→ First highlights where (on the radio), then when (today).
Hoje, na rádio, falam…
→ First highlights when (today), then where (on the radio).

In normal conversation, both word orders are natural and acceptable.

Could you also say “Na rádio, fala‑se hoje sobre ciência e tecnologia”? What’s the difference from “falam”?

Yes, you can say:

Na rádio, fala‑se hoje sobre ciência e tecnologia.

Here, fala‑se is an impersonal “se” construction. It roughly corresponds to English “people talk” / “there is talk” / “they talk” in a more impersonal, neutral way:

Na rádio, fala‑se hoje sobre ciência e tecnologia.
= On the radio, today people are talking / there is talk about science and technology.

Difference from “falam”:

falam: an implicit “they” (the presenters, the station’s people). Still somewhat generic, but grammatically a normal 3rd person plural subject.
fala‑se: no specific subject; it’s more impersonal and often slightly more formal or neutral in tone.

Both are correct; it’s largely a stylistic choice.