No recreio, a professora deu-nos giz para escrever no quadro.

Because Portuguese normally contracts em + o into no.

• em + o = no
• em + a = na
• em + os = nos
• em + as = nas

So:

• no recreio
• no quadro

Using em o here would sound non-standard.

Also, em is the normal preposition in these expressions:

• no recreio = during recess / at break
• escrever no quadro = write on the board

No recreio is a time expression placed at the beginning of the sentence. The comma separates that introductory phrase from the main clause.

So the sentence is structured like this:

• No recreio, = setting the scene
• a professora deu-nos giz... = main information

With short introductory phrases, the comma is sometimes optional, but here it is very natural.

In Portuguese, it is very common to use the definite article before a specific person or thing being talked about.

So a professora means the teacher.

Leaving out the article would usually sound incomplete in this kind of sentence. Portuguese uses articles more often than English does.

Deu comes from the verb dar = to give.

Here, deu is:

• 3rd person singular
• preterite
• meaning gave

So a professora deu = the teacher gave.

It is an irregular past form, so it does not look like the infinitive dar.

Here nos means to us.

The verb dar often works like this:

• dar alguma coisa a alguém = to give something to someone

In this sentence:

• giz = the thing being given
• nos = the people receiving it

So:

• deu-nos giz = gave us chalk

Grammatically, nos is an indirect object pronoun here.

This is a very important feature of European Portuguese.

In an affirmative main clause, object pronouns are often attached after the verb. This is called enclisis.

So in European Portuguese:

• deu-nos

not usually

• nos deu

The hyphen is required in this structure.

This is one of the clearest differences from Brazilian Portuguese, where nos deu is much more common.

In European Portuguese, pronouns move before the verb only in certain situations, for example:

• não nos deu = she did not give us
• quem nos deu? = who gave us?
• quando nos deu... = when she gave us...

But in your sentence, there is no trigger forcing the pronoun before the verb, so deu-nos is the expected form.

Not necessarily. Giz is often used like a mass noun, just like chalk in English.

So deu-nos giz can mean:

• gave us chalk
• gave us some chalk

It does not have to mean exactly one stick.

If you want to count individual pieces, Portuguese can use the plural gizes, but that is not necessary here.

Para + infinitive is used to express purpose:

• para escrever = to write / for writing

In this sentence, the person who will write is understood from context: the people who received the chalk.

So para escrever is perfectly natural.

You could also say:

• para escrevermos no quadro

That version makes we more explicit. It is not wrong; it is just more specific. The original sentence is a little lighter and more neutral.

In a school context, quadro means the classroom board.

Because the sentence uses giz, the most natural interpretation is a chalkboard or blackboard.

So escrever no quadro means writing on the board.

In modern usage, quadro can sometimes refer more generally to the board in the classroom, depending on context.

Yes. Portuguese has fairly flexible word order.

For example, you could also say:

• A professora deu-nos giz no recreio para escrever no quadro.

That is still grammatical.

The original version begins with No recreio to highlight the time setting first. That is a common and natural choice.

In European Portuguese, giz is pronounced roughly like:

• zhish

More precisely:

• the g sounds like the s in measure
• the i is like ee
• the final z is usually pronounced like sh at the end of the word in European Portuguese

So the approximate sound is zhish.