how are electrons arranged around the nucleus?
The correct answer and explanation is:
Electrons are arranged around the nucleus in specific energy levels or orbitals. These energy levels are often referred to as electron shells, and each shell can hold a certain maximum number of electrons. The first shell, which is closest to the nucleus, can hold up to 2 electrons. The second shell can hold up to 8 electrons, the third shell can hold up to 18 electrons, and so on. As the shells get farther from the nucleus, they can accommodate more electrons.
Electrons occupy these energy levels in a way that minimizes the energy of the atom, following a principle known as the Aufbau principle. According to this principle, electrons fill the lowest available energy level first before moving to higher levels. The arrangement of electrons within each shell is further defined by the number of sublevels or orbitals that exist in each shell. For example, the first shell has one sublevel (1s), the second shell has two sublevels (2s and 2p), the third shell has three sublevels (3s, 3p, and 3d), and so on.
Each sublevel consists of orbitals, which are regions of space where electrons are likely to be found. Orbitals are denoted by letters such as s, p, d, and f, with each orbital capable of holding two electrons with opposite spins. The arrangement of electrons in these orbitals follows a set of rules, including the Pauli exclusion principle, which states that no two electrons can have the same set of quantum numbers, and Hund’s rule, which states that electrons fill degenerate orbitals (orbitals of equal energy) singly before pairing up.
The arrangement of electrons determines an atom’s chemical properties. Electrons in the outermost shell, known as valence electrons, are most responsible for chemical bonding and reactivity.