Electron configurations reveal how electrons are arranged in atoms. They follow specific rules like the , , and . Understanding these patterns helps predict an atom's chemical behavior and reactivity.
, found in the outermost , play a crucial role in bonding and chemical reactions. Knowing how to identify and count these electrons is key to understanding an element's properties and its place in the periodic table.
Atomic Structure: Electron Configurations
Order of orbital filling
determines order electrons fill orbitals
Electrons occupy orbitals from lowest to highest energy (1s, 2s, 2p, 3s, etc.)
Prevents electrons from filling higher energy orbitals until lower energy orbitals are filled
energies overlap between different principal quantum numbers (3d < 4s)
notation represents arrangement of electrons in an atom
(n) and sublevel (s, p, d, f) designate each orbital
Superscript indicates number of electrons in the orbital (1s², 2p⁶)
Filled 1s, 2s, and 2p orbitals written as 1s²2s²2p⁶ (neon)
Application of electron configuration rules
limits number of electrons per orbital
Each orbital holds maximum of two electrons with opposite spins (↑↓)
Prevents any two electrons from having identical sets of four quantum numbers
Hund's rule governs distribution of electrons in orbitals of equal energy
Electrons occupy separate orbitals within a sublevel before pairing
Unpaired electrons in the same sublevel have parallel spins (↑↑↑)
Steps for writing electron configurations
Fill orbitals according to the Aufbau principle (lowest to highest energy)
Apply the Pauli exclusion principle (maximum of two electrons per orbital)
Use Hund's rule for electrons in the same sublevel (occupy separate orbitals, parallel spins)
Carbon (6 electrons): 1s²2s²2p² (two unpaired electrons in 2p)
visually represent electron distribution in atomic orbitals
Electrons in outermost shell
Valence electrons are those in the outermost shell of an atom
Determine chemical reactivity and bonding properties of elements
Number of valence electrons varies across the periodic table (1-8)
Finding the number of valence electrons from
Identify the highest principal quantum number (n) in the configuration
Sum the electrons in the s and p sublevels of that principal quantum number
Nitrogen (1s²2s²2p³): 5 valence electrons (2 in 2s and 3 in 2p)
Valence electron configuration simplifies notation for the outermost shell
Inner shell electrons represented by of previous period
Potassium: [Ar] 4s¹ (argon core + one valence electron in 4s)
Energy levels and electron states
Shells represent of electrons around the nucleus
Energy levels increase as distance from the nucleus increases
refers to the lowest energy configuration of electrons in an atom
describes the intrinsic angular momentum of electrons, which can be either up or down
Key Terms to Review (20)
Atomic Orbitals: Atomic orbitals are the wave-like functions that describe the behavior and spatial distribution of an electron in an atom. They are the fundamental building blocks of atomic structure and play a crucial role in understanding chemical bonding and reactivity.
Aufbau principle: The Aufbau principle is a guideline used in organic chemistry to determine the electron configuration of an atom, molecule, or ion. It states that electrons occupy the lowest energy orbitals first before filling higher energy levels.
Aufbau Principle: The Aufbau principle is a fundamental concept in quantum mechanics that describes the order in which electrons occupy atomic orbitals. It is a crucial principle that governs the electron configurations of atoms and is closely tied to the understanding of atomic structure and chemical bonding.
Electron configuration: Electron configuration describes the distribution of electrons in an atom's atomic orbitals. It follows a set of rules, including the Pauli exclusion principle and Hund's rule, to show how these electrons are arranged around the nucleus.
Electron Configuration: Electron configuration refers to the arrangement of electrons in an atom's orbitals, which determines the atom's chemical properties and behavior. This concept is central to understanding the structure and behavior of atoms, as well as the formation of chemical bonds and the properties of molecules.
Electron shell: An electron shell is a group of atomic orbitals with the same principal quantum number, n, indicating its distance and energy level relative to the nucleus in an atom. These shells define the distribution of electrons around an atom's nucleus and are crucial for determining how atoms interact in chemical bonding.
Electron Spin: Electron spin is a fundamental property of electrons that describes their intrinsic angular momentum. It is a quantum mechanical property that arises from the behavior of electrons at the subatomic level, and it is a crucial concept in understanding the structure and behavior of atoms and molecules.
Energy Levels: Energy levels refer to the discrete, quantized states that electrons can occupy within an atom. These energy levels are associated with the specific amount of energy required for an electron to exist in a particular orbital or shell around the nucleus of an atom. The concept of energy levels is fundamental to understanding atomic structure and the behavior of electrons in chemical reactions and spectroscopic phenomena.
Ground State: The ground state is the lowest possible energy level that an atom or molecule can occupy. It represents the most stable configuration of the electrons within the system, where the total energy is minimized.
Ground-state electron configuration: The ground-state electron configuration is the arrangement of electrons in an atom's orbitals when it is at its lowest energy level. It determines the chemical properties and reactivity of the element.
Hund’s rule: Hund's rule states that every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin. This principle minimizes electron-electron repulsions and stabilizes the atom.
Hund's Rule: Hund's rule is a fundamental principle in quantum mechanics that describes the electronic configuration of atoms. It states that when electrons occupy degenerate orbitals, they will occupy these orbitals singly with parallel spins before pairing up.
Noble Gas Configuration: The noble gas configuration refers to the electron arrangement in an atom that is the same as the electron configuration of a noble gas element. This configuration is a stable and low-energy state for an atom, as the noble gases have a full valence shell of electrons.
Orbital Diagrams: Orbital diagrams are visual representations of the arrangement and distribution of electrons within the atomic orbitals of an element. They provide a way to depict the electron configuration of an atom, showing the specific energy levels and sublevels occupied by the electrons.
Pauli exclusion principle: The Pauli Exclusion Principle states that no two electrons in an atom can have the same set of four quantum numbers. This principle helps determine electron configurations within atoms, crucial for understanding chemical bonding and molecular structure in organic chemistry.
Pauli Exclusion Principle: The Pauli exclusion principle is a fundamental principle in quantum mechanics that states that no two identical fermions (particles with half-integer spin) can occupy the same quantum state simultaneously. This principle has far-reaching implications for the structure of atoms, the organization of the periodic table, and the behavior of chemical bonds.
Principal Quantum Number: The principal quantum number is a fundamental concept in atomic structure that describes the energy level or shell of an electron within an atom. It is a key parameter that determines the overall energy and spatial distribution of electrons in an atom.
Shell: The shell of an atom refers to the distinct energy levels or regions surrounding the nucleus where electrons are found. Electrons are organized into shells based on their energy levels, with the innermost shell being the lowest energy level and the outermost shells representing higher energy levels.
Sublevel: A sublevel is a subdivision within an electron shell or energy level in an atom. It is a more specific classification of the possible electron configurations within a given energy level.
Valence Electrons: Valence electrons are the outermost electrons in an atom that participate in chemical bonding. They are the electrons that determine the chemical properties and reactivity of an element.