There are eleven obligatory acts for prayers:
Niyyat (intention)
Qiyam (standing erect)
Takbiratul Ehram (saying Allahu Akbar while commencing the prayers)
Ruku' (bowing)
Sajdatayn (two prostration)
Qira'at (recitation of Surah al-Hamd and other surah)
Zikr (prescribed recitation in Ruku' and Sajdah)
Tashahhud (bearing witness after completing the Sajdah of the second and the last Rak'at)
Salaam (Salutation)
Tartib (sequence)
Muwalat (to perform the different acts of prayers in regular succession).
951. Some of the obligatory acts of prayers are elemental (Rukn). Hence, a person who does not offer them, whether intentionally or by mistake, his prayers become void. Some other obligatory acts of prayers are not elemental. Therefore, if they are omitted by mistake, the prayers does not become void.