Remember that motifs are recurrent elements that are "tangible" (so to speak): narrative events, characters, objects, lines of dialog, etc.
Themes are more abstract than motifs. They are the general subjects addressed by works of art. "Love", "truth", "freedom vs. the requirements of society" are a few examples of themes one may easily find in novels, poems or movies.
Themes are made up of motifs. That's why, when identifying themes or motifs, it's always a good a idea to ask oneself questions like these: What theme (or themes) does this motif refer to? What motif (or motifs) constitute this theme?
This list of themes and motifs is by no means exhaustive. It's just an account of a series of elements that seem particularly salient to me and that I have found useful to consider when teaching the novel. I invite you to share other aspects you may have found relevant.
History and fiction
In the first 5 chapters of the novel there's an interesting interplay between history and fiction. This overarching theme is developed through several motifs, both geographical and historical.For instance, when the narrator tells us that the pirate Sir Francis Drake attacked Riohacha in the sixteenth century (p.19), we are presented with a historical fact embedded in sheer fiction. Riohacha did exist in the sixteenth century (and still does) and this attack did take place in 1596.
Sir Francis Drake's attack, a historical fact, becomes an important event in the novel, too. It is the first event in a series of cause-effect chains that ends up with the founding of Macondo.
The following excerpt demonstrates how history and fiction are intermingled in the narrative: "Several centuries later the great-great-grandson of the native-born planter married the great-great-granddaughter of the Aragonese. Therefore, every time that Úrsula became exercised over her husband's mad ideas, she would leap back over three hundred years of fate and curse the day that Sir Francis Drake had attacked Riohacha" (p.20).
Even though Macondo is a fictional town, its surroundings are geographically identifiable in "the real world". This becomes particularly evident when you compare a map of the fictional geography of the novel to the actual map of the Colombian Caribbean coast:Macondo is surrounded by the Sierra Nevada de Santa Marta and by the Ciénaga Grande de Santa Marta. In the English version of the novel, the former is presented simply as "the mountains" and the latter as the "swamp".
The theme of "isolation", developed throughout the first chapters, is related to both geographical and historical remoteness. Both aspects were one of the main features of Colombian history and geography up to very recent times, when air travel finally connected our different regions to one another and the country to the rest of the world.
At the end of chapter 2, when looking for her son that had fled with the gypsies, Úrsula manages to break this isolation without having even intended to do it. She accidentally succeeds in connecting Macondo to the world, something José Arcadio kept trying to do in vain with his inventions and enterprises:
"They came from the other side of the swamp, only two days away, where there were towns that received mail every month in the year and where they where familiar with the implements of good living. Úrsula had not caught up with the gypsies, but she had found the route that her husband had been unable to discover in his frustrated search for the great inventions"(p.36).