Science

Atomic mass

In this Class 9 Science topic from Atomic Foundations of Matter, students learn how the mass of an atom is represented and compared. The concept uses the atomic mass unit (u), defined with reference to one-twelfth of the mass of a carbon-12 atom. Students distinguish atomic mass from atomic number and mass number, understand why an element’s atomic mass may be a weighted average of its isotopes, and apply these ideas to interpret chemical data and calculate relative atomic or molecular masses.