Answer is daltons Atomic weight is measured in atomic mass units (amu), also called daltons.
Atomic Mass
Masses of individual atoms are very, very small. Using a modern device called a mass spectrometer, it is possible to measure such minuscule masses. An atom of oxygen-16, for example, has a mass of 2.66 × 10 -23 g. While comparisons of masses measured in grams would have some usefulness, it is far more practical to have a system that will allow us to more easily compare relative atomic masses. Scientists decided on using the carbon-12 nuclide as the reference standard by which all other masses would be compared. By definition, one atom of carbon-12 is assigned a mass of 12 atomic mass units (amu). An atomic mass unit is defined as a mass equal to one twelfth the mass of an atom of carbon-12. The mass of any isotope of any element is expressed in relation to the carbon-12 standard. For example, one atom of helium-4 has a mass of 4.0026 amu. An atom of sulfur-32 has a mass of 31.972 amu.
The universal mass unit, abbreviated u (sometimes amu for atomic mass unit), is defined as one-twelfth of the mass of the 12C atom which has been defined to be exactly 12 u. The absolute mass of a 12C atom is obtained by dividing the value 12 by the Avogadro number (NA = 6.022 137 × 1023).
A Lewis base is characterized as any species that can donate a lone pair of electrons the Lewis acid (which has a vacant orbital for the lone pair to bond with)
