Algunos(as) and unos(as) are indefinites that tend to be used interchangeably, and most of the time this is correct. However, it is important to know that they are also used differently in some contexts. In this article, let's review the three main differences that will help you distinguish when to use them.
Algunos de los empleados no están satisfechos.
Some of the employees are not satisfied.
Hay unas dos mil personas en el estadio.
There are about two thousand people in the stadium.
When Talking About Approximations
Rule 1. One of the main differences is that unos and unas are used with numbers and approximations. In this case, its English translation, for example, would not be "some" but "about." In this case, it can be used as follows:
Hay + unos, unas + number
Hay unas 540,000 especies marinas en el mar.
There are about 540.000 marine species in the sea.
Rule 2. It is also common to find unos/unas with verbs related to money or numbers, such as ganar, comprar, perder, apostar, etc.
En 2013, Rhonda compró tres bitcoins y medio por el precio de unos 80 dólares cada uno.
In 2013, Rhonda purchased three and a half bitcoins for the price of about $80 each.
When Followed by the Preposition De
Rule 3. If the word that follows is the preposition de, the correct collocation is with algunos or algunas.
Quizá algunos de ellos saben hablar español.
Perhaps some of them can speak Spanish.
As an Intensifier
Rule 4. When you want to emphasize a characteristic in informal language, you use unos or unas. In this case, it would translate more as such a.
Eres un bobo, siempre haciendo chistes de papá.
You're such a goof, always making dad jokes.
Hay ____ 500 alumnos en este evento.