Final answer:
The concept of "missing" mass in lithium atoms can be explained by understanding the different isotopes of lithium. A lithium atom always contains 3 protons, giving it an atomic number of 3. However, the mass number can vary depending on the number of neutrons.
Step-by-step explanation:
The concept of "missing" mass in lithium atoms can be explained by understanding the different isotopes of lithium. A lithium atom always contains 3 protons, giving it an atomic number of 3. However, the mass number can vary depending on the number of neutrons. For example, the isotope lithium-6 has 3 protons and 3 neutrons, while lithium-7 has 3 protons and 4 neutrons.
When we compare the combined mass of 3 protons and 3 electrons to the actual mass of a lithium-6 atom, we find that the mass of the lithium-6 atom is slightly less. This is because a small amount of mass is lost during the formation of a lithium-6 atom due to the conversion of mass into energy.
To measure this missing mass, scientists use atomic mass units (u), with 1 atomic mass unit equivalent to 1/12th the mass of a carbon-12 atom. The actual mass of a lithium-6 atom is approximately 6.015 u, which is slightly less than the combined mass of 3 protons and 3 electrons.