An atom with 3 protons is indeed a lithium atom. Lithium is a chemical element with the atomic number 3, which means it has 3 protons in its nucleus. The number of neutrons can vary among isotopes of an element.
However, the statement "an atom with 3 protons and 3 neutrons" does not represent a stable isotope of lithium. The most common isotope of lithium, known as lithium-7, has 3 protons and 4 neutrons, resulting in a total of 7 nucleons (protons + neutrons). So, an atom with 3 protons and 4 neutrons is a lithium-7 atom.
Isotopes are variants of an element that have the same number of protons but different numbers of neutrons. While lithium-7 is the most abundant and stable isotope of lithium, there are other isotopes of lithium with different neutron numbers, such as lithium-6 with 3 protons and 3 neutrons.
To summarize:
- An atom with 3 protons and 3 neutrons does not represent a stable lithium isotope.
- An atom with 3 protons and 4 neutrons is the most common and stable isotope of lithium, known as lithium-7.