What are the elements of music in the 20th century?

Atonality - composing music with no tonal center. Using dissonant chords

Twelve tone method - composing music using a tone row of chromatic tones that stay in order throughout the piece. The tone row can appear in retrograde, inversion, and retrograde inversion

Expressionism - using music to express the composer's emotion and state of mind

Impressionism - using tone color to create a feeling similar to those of Impressionistic paintings. The harmonies are brief and hazy sounding.

Chance music - the composer only dictates a portion of the elements of the composition. The rest is up to the musicians or the audience.

Minimalism - music that may include the repetition of a phrase or specific tone, droning or steady long tones, constant harmony and a steady pulse