Described as the atmosphere of a piece of writing, the mood of a literary work has to do with the emotions a literary piece arouses in a reader.
In the first three chapters of The Great Gatsby, there is a dark mood because of ambiguity, superficiality, greed, and moral decadence. There is also in Fitzgerald's writing evidence of his gift for evocation as he brings to life the Jazz Age, its restlessness, and its insatiable appetite for materialism and pleasure.
The first three chapters reflect this restlessness, "the foul dust" of materialism, and the superficiality and decadence of the twenties. In chapter one during Nick Carraway's visit to "two old friends whom [he] scarcely knew at all," there is a mood of superficiality. This superficiality is conveyed by Nick's comment about his "two old friends" that he does not know, along with his description of the Buchanan's Georgian Colonial mansion. Tom Buchanan stands on the front porch wearing a riding habit, as though he were the owner of a large plantation. "I've got a nice place here," he says, his eyes flashing about restlessly. Later, Nick observes, "He had changed since his New Haven years." Nick then points to Tom's "fractiousness" and "touch of paternal contempt...even toward people he liked."
Inside the mansion, Daisy Buchanan and Jordan Baker exhibit a certain superficiality and jaded quality. Nick observes,
Sometimes she and Miss Baker talked at once, unobtrusively and with a bantering inconsequence that was never quite chatter, that was as cool as their white dresses and their impersonal eyes in the absence of all desire.
When Nick looks at Miss Baker's "glowing face" he is "compelled forward breathlessly." However, as he listens to her, the glow soon fades, thus conveying her shallowness:
...deserting her with lingering regret like children leaving a pleasant street at dusk.
In chapter two, the mood of decadence is conveyed by the "grey land and spasms of bleak dust" covering the dumping ground for industrial and material waste. Also, Tom Buchanan takes Nick with him as he picks up his mistress, Myrtle Wilson. Again, Buchanan demonstrates his superficiality and insincerity when he speaks to George Wilson, Myrtle's husband, about buying an automobile from him. At the same time, he is having an affair with the man's wife. Then, too, Myrtle is herself superficial as she acts as though she is among the upper class while with guests at the hotel room in New York City. For instance, she changes into an elaborate dress, and her voice assumes "an impressive hauteur" as she converses with the others.
In chapter three, the mood of decadence continues with yellow imagery which conveys luxury, hedonism, and falsity. Simply so he can showcase his wealth, Gatsby stages parties to which strangers simply arrive. Almost no one is actually invited, suggesting the superficiality of the affair. Also, there is an excessiveness that connotes decadence and immorality:
At least once a fortnight a corps of caterers came down with several hundred feet of canvas and enough colored lights to make a Chrismas tree of Gatsby's enormous garden.
Tables of food abound and there are meats and platters of fowl of all kinds. A five piece orchestra arrives, and there are "enthusiastic meetings of women who do not even know each other's names." One of the few invited guests, Nick, hears strange people talking. He observes,
I was sure that they were all selling something: bonds or insurance or automobiles. They were, at least, agonizingly aware of the easy money in the vicinity and convinced that it was theirs for a few words in the right key.
Married men flirt with young single women who wander about the premises. Nick overhears one say, "I never care what I do, so I always have a good time." Amid all this shallow talk, there are "vacuous bursts of laughter."
Other guests whisper rumors about their host, Mr. Gatsby. Nick observes,
It was testimony to the romantic speculation he inspired that there were whispers about him from those who had found little that it was necessary to whisper about in this world.
Lacking Gatsby's romantic vision, Nick sees life in the East Egg as petty, ambiguous, superficial, and amoral. The first three chapters of Fitzgerald's narrative aptly depicts the superficiality of people and their decadent, immoral behavior.