The main difference between the two types is the rhyme plot. The Petrarchan sonnet has a rhyme arrangement of ABBAABBA where the lines ending in A rhyme with each other, just as do lines ending in "B.” The Shakespearean sonnet has an interchanging rhyme scheme of ABABCDEFEFGG, finishing with a rhyming couplet. Both sonnet types are always written in iambic pentameter, pairs of stressed and unstressed syllables, in every line.
Above this, and perhaps shared subject matter, the two differ significantly in their forms while still deemed the identical type of poem. The specificity of the Petrarchan rhyme scheme, which was named for and created by the Italian poet Petrarch works well with the Italian language as it has the ability to rhyme.