Final answer:
Atomic mass correlates with atomic radius as heavier atoms generally have a larger radius. The atomic mass of elements is approximately equal to their mass numbers, but it is often not a whole number due to the presence of isotopes. Elements that are radioactive have atomic mass given in square brackets, representing the mass number of the most stable isotope.
Step-by-step explanation:
The atomic mass of an element can be correlated with its atomic radius, with certain trends apparent in the periodic table. Periodic Table color-coded for atomic mass, you'll notice that elements at the bottom have a greater atomic mass compared to elements at the top. This is one key reason heavier atoms with more protons and neutrons generally have a larger atomic radius due to increased levels of electron shell occupation.
Understanding Atomic Mass
Atomic mass is approximately equal to the mass number of an atom, which is the sum of protons and neutrons. Each proton and neutron contributes roughly one atomic mass unit (amu). Electrons contribute much less due to their negligible mass. The average mass of most elements is not a whole number because they exist as mixtures of isotopes, each with a different number of neutrons.
Radioactive Isotopes and Atomic Mass
Some elements with higher atomic numbers, like technetium and promethium, and all substances from polonium and higher, display their atomic masses in square brackets in the periodic table. This indicates these elements consist entirely of unstable, radioactive isotopes, which can't have an average atomic weight due to varied isotope abundance or non-existence in nature. The square brackets denote the mass number of the most stable isotope.