One of the most common errors I see in my students’ writing is the combining of “a lot” into one word (that doesn’t actually exist): “alot.”
The main difference between “alot” and “a lot” is that one is a word, and one is not.
Many of us are so accustomed to seeing “alot” that we ascribe to the misconception that it’s a word, but–surprise!–it’s not. The proper way to employ “alot” is actually to separate it into two words, a noun and its article: “a lot.” One helpful way to remember this is to think of a plot (or a lot) of land. If you own one lot of land, you own a lot of land, but not onelot of land, or alot of land. Just as you would not write “onelot,” you would not write “alot.” The proper structure is, instead “one lot” and “a lot.” Another way to think of it is this: You wouldn’t write “alittle,” so you also wouldn’t write “alot.”