Some and some of
APRIL 9, 2012
Before a noun with a determiner (articles, demonstratives and possessive pronouns), we use some of. If there is no determiner we use some.

Some of my friends live abroad. (NOT Some my friends live abroad.)
I have bought some apples. (NOT I have bought some of apples.)
Some people want a new system. (NOT Some of people want a new system.)
Some of is also used before a pronoun.

Some of us want a new system. (NOT Some us want a new system.)
Nouns can be dropped after some, if the meaning is clear.

I have bought too many chocolates. You can have some. (OR You can have some of them.)
Some with singular countable noun

With a singular countable noun, some can refer to an unknown person or thing.

Some idiot has let the cat in.
There must be some job for me.
She is living in some city in Japan.
Some can mean ‘quite a’ in informal American English.

It was some evening! (= It was quite an evening.)
Some can also be used to suggest that we do not think much of somebody or something.

I don’t want to waste the rest of my life doing some boring jobs.
She is going to marry some farmer in Kenya.
Some can be used with a number to suggest that the number is an impressive one.

We have already sold some twenty thousand copies of this book.