Let's examine the potential changes to an atom of beryllium-9 (Be-9) based on your scenarios:
If the atom of beryllium-9 had one more proton: Adding one more proton would change the atomic number of the atom. Beryllium-9 has an atomic number of 4, which means it normally has four protons. By adding one more proton, the atomic number would increase to 5, making it an atom of boron-9 (B-9). Boron-9 would have properties distinct from beryllium due to its different number of protons, impacting its chemical behavior.
If the atom of beryllium-9 had one less neutron: Beryllium-9 normally has four protons and five neutrons, giving it a total of nine particles in the nucleus. If it were to lose one neutron, the number of neutrons would decrease to four, resulting in an isotope of beryllium with a mass number of 8 (Be-8). This change in the number of neutrons would not significantly affect the atom's chemical properties since neutrons do not participate directly in chemical reactions. However, it would alter its stability and nuclear properties.
If the atom of beryllium-9 had one more electron: The number of electrons in an atom determines its charge and chemical behavior. Beryllium-9 normally has four electrons to balance its four protons. If it were to gain one more electron, the resulting ion would have a net negative charge. Specifically, it would become a negatively charged beryllium ion (Be-9 with an extra electron) or an oxide ion (O2-) if it gained the electron from an oxygen atom, for example. The additional electron would impact the atom's reactivity and interaction with other atoms in chemical reactions.
It's important to note that changes in the number of protons or neutrons would result in different isotopes of beryllium, while changes in the number of electrons would create charged particles or ions. These changes can influence an atom's properties, such as its stability, chemical behavior, and reactivity.