Toda a vizinhança ficou em silêncio quando a reunião começou.

Because vizinhança is a singular collective noun here. It refers to the whole neighborhood or all the people in the surrounding area as one group.

So:

• toda a vizinhança = the whole neighborhood / everyone in the neighborhood
• todas as vizinhanças would mean all the neighborhoods, which is a different idea

In Portuguese, it is very common to use a singular noun this way when talking about a group as a whole.

In Brazilian Portuguese, when todo/toda means the whole / entire, it is often used with a definite article:

• todo o dia = the whole day
• toda a cidade = the whole city
• toda a vizinhança = the whole neighborhood

Without the article, todo/toda can sometimes mean every / any, depending on the context:

• toda cidade tem problemas = every city has problems

So in your sentence, toda a vizinhança clearly means the entire neighborhood.

It can suggest both, but in this sentence it most naturally refers to the people in the neighborhood.

Literally, vizinhança is neighborhood or vicinity, but Portuguese often uses it to mean the people associated with that area too.

So toda a vizinhança ficou em silêncio is understood as:

• the whole neighborhood fell silent
• in natural English, that really means all the neighbors / everyone nearby became silent

Both are in the preterite in Brazilian Portuguese.

• ficou = from ficar
• começou = from começar

The preterite is used for completed actions or events seen as whole and finished in the past.

Here:

• a reunião começou = the meeting started
• a vizinhança ficou em silêncio = the neighborhood became / fell silent

These are both treated as completed past events.

Because ficou emphasizes a change of state.

• ficar em silêncio = to become silent / to fall silent
• estar em silêncio = to be silent

So:

• A vizinhança ficou em silêncio = they became silent
• A vizinhança estava em silêncio = they were silent

In your sentence, the idea is that when the meeting started, there was a change: people stopped making noise and became quiet.

Ficar has several common meanings in Portuguese, and this is one of the most important verbs to learn because it is very flexible.

Some common uses are:

• ficar = to stay
  • Vou ficar em casa.
• ficar = to become
  • ficou triste = became sad
  • ficou em silêncio = became silent
• ficar = to be located
  • Onde fica o banco? = Where is the bank?

So here, ficou em silêncio uses the become meaning.

It is literally in silence, but in natural English it often works like silently or in silence, depending on the sentence.

Examples:

• Ele entrou em silêncio. = He entered silently / in silence.
• A sala ficou em silêncio. = The room fell silent.

In your sentence, ficou em silêncio is an idiomatic and very natural expression meaning became silent.

Portuguese uses definite articles much more often than English does.

So a reunião começou is perfectly normal and usually the most natural choice in Portuguese, even when English would simply say the meeting started or sometimes just meeting started in a very informal style.

The article a tells us we are talking about a specific meeting already known in the context.

Normally, no. In standard Portuguese, quando a reunião começou is the correct form.

Leaving out the article here sounds unnatural because reunião is a countable noun and refers to a specific event.

So use:

• quando a reunião começou

not:

• quando reunião começou

Because the sentence refers to a specific moment in the past when the meeting started.

• quando a reunião começou = when the meeting started

The start of a meeting is a single completed event, so the preterite fits well.

If you used the imperfect, such as começava, it would suggest a repeated action, background description, or a less clearly bounded event, which does not fit this sentence as naturally.

Yes. That version is completely natural and means the same thing.

You can say:

• Toda a vizinhança ficou em silêncio quando a reunião começou.
• Quando a reunião começou, toda a vizinhança ficou em silêncio.

The second version puts more focus on the time clause first. Portuguese allows this kind of movement very easily.

Yes, in many contexts you can.

• toda a vizinhança
• a vizinhança toda

Both can mean the whole neighborhood.

However, toda a vizinhança is a little more neutral and often more common in formal or standard phrasing. A vizinhança toda can sound slightly more conversational or emphatic.

So your original sentence sounds very natural as written.

A simple pronunciation guide is:

TO-da a vee-zee-NYAN-sa fee-KOH eem see-LEN-see-oh KWAN-doo a heh-u-nee-OWN koh-meh-SOW

A few useful notes:

• vizinhança has the stressed syllable on nhan
• reunião has nasal sound at the end: -ão
• começou is stressed on the last syllable: çou
• In natural speech, toda a may sound linked together smoothly

A more natural rhythm would be something like:

Toda a vizinhança ficou em silêncio / quando a reunião começou.

Yes, it is fully natural and correct.

It sounds like normal written or spoken Brazilian Portuguese and uses very common structures:

• toda a + noun
• ficar em silêncio
• quando + past action

So this is a good sentence to learn from because it contains very useful everyday grammar and vocabulary.