Three differences:
DNA and RNA are composed of repeated units. RNA is ribonucleotide monophosphates: and in DNA are 2 deoxyribonucleotide monophosphates.
The sugar in DNA is deoxyribose; the sugar in RNA is ribose. (Biggest difference between DNA/RNA)
And,finally,
Nitrogen bases of DNA: Adenine, Guanine, Cytosine, and Thymine.
Nitrogen bases of RNA: Adenine, Guanine, Cytosine, and Uracil.
These are the three main chemical differences between DNA and RNA.