If an atom of beryllium-9 (9Be) were to gain one more proton, it would become an atom of boron-10 (10B). This is because the number of protons determines the atomic number of an element. Beryllium has an atomic number of 4, which means it has four protons in its nucleus. Adding one more proton would increase the atomic number to 5, resulting in boron.
If an atom of beryllium-9 were to have one less neutron, it would still be considered beryllium, but it would be a different isotope. Beryllium-9 normally has four protons and five neutrons. Removing one neutron would result in an isotope with four protons and four neutrons, known as beryllium-8 (8Be). Beryllium-8 is unstable and undergoes rapid decay.
If an atom of beryllium-9 were to gain one more electron, it would become negatively charged and form an ion. It would be denoted as Be-9 with a negative charge, written as Be-9-. This negatively charged ion would exhibit different chemical behavior compared to a neutral beryllium atom. It would be attracted to positively charged species and participate in ionic bonding with other elements.