A blog can be written with a word count range of at least 300 up to 500. Blogs can be written with a casual and laid back feel as if your are talking to one person and having a conversation.
A blog can be written and updated as often as you need to and spelling and grammar aren't that important.
A blog also can have videos and info graphics that you can write your own content around.
Probably, A Blog is a Collection and Creation of Articles about Different Topics or may be similar Topics, but the content in every article vary as per it's constructiveness.
Articles on the other hand a different because they can be written with a higher word count range of 500 up to 2,500 words.
Articles require great spelling and grammar for your reader to understand.
Articles are more written with full description and detail that is more like talking to people and not conversational.
However, an Article is nothing but a brief description about whole and sole of a Topic and its history or about its operation or construction or development, whatever it may be.