Determining the exact and absolute mass of an individual atom is a challenging task. However, scientists have been able to measure atomic masses with high precision using a technique called mass spectrometry. Here's a brief overview of how this method works:
Isolation: The atom of interest is isolated, either by vaporizing a sample or by ionizing the atoms in a gas phase.
Ionization: The isolated atoms are bombarded with high-energy electrons, which can knock off one or more electrons from the atom, resulting in the formation of positive ions.
Acceleration: The positive ions are then accelerated using an electric field, which imparts them with kinetic energy.
Deflection: The accelerated ions pass through a magnetic field perpendicular to their direction of motion. The magnetic field causes the ions to experience a force perpendicular to both their velocity and the magnetic field. This force causes the ions to move in a curved path.
Detection: The ions with different masses and charges have different curvatures due to their differing ratios of mass to charge. These ions are detected by a detector, which records their arrival times and intensities.
Analysis: The data obtained from the detection process is used to calculate the mass-to-charge ratio (m/z) for each ion. By comparing the observed mass-to-charge ratios with known standards, the actual mass of the atom can be determined.
It's important to note that while mass spectrometry provides accurate measurements of atomic masses, it still relies on relative comparisons to known standards. The carbon-12 isotope (with a mass of exactly 12 atomic mass units) is often used as a reference point in mass spectrometry.