Austen creates the atmosphere of the time period in which she sets the story by the way she crafts her characters and the various settings in the novel. Austen is a master of characterization and uses all of the tools available to her. When you consider a character like Mrs. Bennet, the audience very quickly understands the social expectations for marriage of young women and the financial necessity of marrying well for girls who will not have an inheritance. Mrs. Bennet acts in a silly manner, but at the heart of her speech and her actions is a mother who has very real concerns for her daughters. Austen also creates atmosphere in having each of the Bennet daughters speak about their attitudes about marriage. These attitudes are contrasted with those of Charlotte Lucas who has a more practical nature and represents the attitudes of many young women of the time period.
The atmosphere of the social climate is created in each scene of a social gathering. The "rules" of behavior are drawn out at the first ball. This is further drawn at the Netherfield Ball chapter. Smaller measures of social climate are drawn at dinner parties such the time Elizabeth spends at Netherfield during Jane's recuperation and at the larger dinner party at Lady Catherine's later in the novel.
The difference in social classes and wealth are illustrated by Austen's descriptions of each of the major homes in the novel. There is a striking difference between Longbourne, Netherfield, Rosings, and Pemberly, not to mention, Charlotte's home with Collins, and other smaller residences. Austen makes the difference in social classes very clear.
The overall atmosphere of the novel doesn't change in regards to any of the above topics. What does change is Elizabeth and Darcy's attitudes about the importance of these things. While they will always be from different classes and backgrounds, their attitudes about whether those things are important does change. Elizabeth realizes that Darcy is wealthy, but not as arrogant as he once appeared, and Darcy realizes that Elizabeth possesses a nobility that has nothing to do with her birth.