The atomic weight of an element, in its most stable form, represents the weighted average of the atomic masses of all naturally occurring isotopes of that element. The atomic weight is determined by considering the relative abundances of each isotope found in nature.
For example, let's consider the atomic weight of carbon. Carbon has two stable isotopes: carbon-12 and carbon-13. Carbon-12 is more abundant, with a natural abundance of approximately 98.9%, while carbon-13 has a natural abundance of about 1.1%.
To calculate the atomic weight of carbon, we take into account the mass of each isotope and its relative abundance. The atomic mass of carbon-12 is defined as exactly 12 atomic mass units (u), and the atomic mass of carbon-13 is approximately 13.00335 u.
The calculation for the atomic weight of carbon would be as follows:
Atomic weight of carbon = (Atomic mass of carbon-12 × abundance of carbon-12) + (Atomic mass of carbon-13 × abundance of carbon-13)
= (12 u × 0.989) + (13.00335 u × 0.011)
= 12.01 u
Therefore, the atomic weight of carbon, in its most stable form, is approximately 12.01 atomic mass units.
The atomic weight of an element can vary depending on the isotopic composition and the relative abundances of its isotopes. Different elements may have different atomic weights due to the specific isotopes they possess and their respective abundances.