Selenium, an element found in the Earth’s crust, plays various roles in nature and technology. Understanding its fundamental building blocks—protons, neutrons, and electrons—provides insight into its chemical behavior. These subatomic particles dictate how selenium interacts with other elements, forming compounds with applications.
Protons in Selenium
Every atom of selenium contains 34 protons. This specific number is its atomic number, which identifies selenium. This means any atom with 34 protons is selenium. Protons are subatomic particles located within the atom’s nucleus, carrying a positive electrical charge.
Electrons in Selenium
A neutral selenium atom possesses 34 electrons. In a neutral atom, the number of negatively charged electrons matches the number of positively charged protons. Electrons are subatomic particles that occupy regions of space, called orbitals, around the atomic nucleus. Their arrangement and behavior are important to how selenium forms chemical bonds with other elements.
Neutrons in Selenium
The number of neutrons in a selenium atom can vary, leading to different forms of the element known as isotopes. Neutrons are subatomic particles found in the nucleus alongside protons, but they carry no electrical charge. While they do not affect an element’s identity, neutrons contribute to an atom’s mass. The number of neutrons in an isotope is determined by subtracting the atomic number (number of protons) from its mass number.
Selenium has several naturally occurring isotopes. The most abundant is Selenium-80 (⁸⁰Se), which accounts for nearly half of all natural selenium atoms. This isotope contains 46 neutrons (80 mass units – 34 protons = 46 neutrons). Other common stable isotopes include:
- Selenium-78 (⁷⁸Se) with 44 neutrons
- Selenium-76 (⁷⁶Se) with 42 neutrons
- Selenium-77 (⁷⁷Se) with 43 neutrons
- Selenium-74 (⁷⁴Se) with 40 neutrons
- Selenium-82 (⁸²Se) with 48 neutrons
These variations explain why the atomic mass of selenium on the periodic table is an average value reflecting the natural abundance of its isotopes.
Selenium Ions
Selenium atoms can gain or lose electrons to form electrically charged particles called ions. While the number of protons and neutrons remains constant during this process, the electron count changes, leading to a net positive or negative charge. Atoms form ions to achieve a more stable electron configuration, often by filling their outermost electron shell.
A common ion formed by selenium is the selenide ion, represented as Se²⁻. This ion forms when a neutral selenium atom gains two electrons. By acquiring these two negatively charged particles, the selenide ion achieves a stable electron arrangement, similar to that of a noble gas.