No, all atoms do not have the same mass. The mass of an atom depends on the type of atom and the specific isotope of that element. Atoms are composed of protons, neutrons, and electrons. Protons and neutrons, collectively called nucleons, are located in the nucleus of an atom, while electrons orbit around the nucleus.
The mass of an atom is primarily determined by the sum of the masses of its protons and neutrons, as electrons have a negligible mass in comparison. Protons and neutrons have similar masses, but they are not identical. The mass of a proton is approximately 1 atomic mass unit (amu), while the mass of a neutron is slightly larger, around 1.008 amu. In comparison, the mass of an electron is about 1/1836 amu.
Different elements have different numbers of protons, which define their atomic number, and thus, their chemical identity. However, the number of neutrons can vary within the same element, resulting in different isotopes. Isotopes of an element have the same number of protons but different numbers of neutrons. These variations in neutron number lead to differences in atomic mass.
For example, carbon typically has six protons and six neutrons, resulting in an atomic mass of around 12 atomic mass units. However, there are also carbon isotopes with seven or eight neutrons, resulting in carbon-13 and carbon-14, respectively. These isotopes have different atomic masses, with carbon-13 having a mass of approximately 13 atomic mass units and carbon-14 having a mass of around 14 atomic mass units.
In summary, the mass of an atom is determined by the number of protons and neutrons it contains, and different elements and isotopes can have different masses.