Atoms are like puzzles, with electrons as the pieces. They follow rules to fit together, filling energy levels from lowest to highest. This dance of electrons shapes an atom's properties and behavior.
The periodic table is a map of these electron arrangements. Elements in the same group share similar outer electron setups, giving them alike chemical traits. It's a handy tool for predicting how atoms will interact.
Electronic Structure of Atoms
Electron configuration principles
- Aufbau principle states electrons fill orbitals (specific regions where electrons are likely to be found) in order of increasing energy (1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f) occupying the lowest energy orbitals available first
- Hund's rule maximizes the number of unpaired electrons in a sublevel by filling orbitals of equal energy singly before pairing up minimizing electron-electron repulsion
- Pauli exclusion principle allows a maximum of two electrons with opposite spins in each orbital no two electrons in an atom can have the same set of four quantum numbers
- Writing electron configurations involves determining the number of electrons in the atom based on its atomic number filling orbitals according to the Aufbau principle and Hund's rule representing the number of electrons in each sublevel (a group of orbitals with the same energy level) with a superscript (Carbon with Z=6 has the electron configuration 1s²2s²2p²)
Quantum numbers and electron properties
- Quantum numbers describe the properties and behavior of electrons in atoms
- Principal quantum number (n) represents the main energy level of an electron
- Angular momentum quantum number (l) describes the shape of the orbital
- Magnetic quantum number (ml) indicates the orientation of the orbital in space
- Spin quantum number (ms) specifies the direction of electron spin (up or down)
Anomalous configurations in elements
- Anomalous electron configurations like those of chromium and copper deviate from the expected filling order when the energy difference between two sublevels is small
- Half-filled or completely filled sublevels are more stable leading to these anomalies
- Chromium (Z=24) has an actual configuration of [Ar]3d⁵4s¹ instead of the expected [Ar]3d⁴4s² one electron from the 4s sublevel is promoted to the 3d sublevel to achieve a half-filled 3d sublevel
- Copper (Z=29) has an actual configuration of [Ar]3d¹⁰4s¹ instead of the expected [Ar]3d⁹4s² one electron from the 4s sublevel is promoted to the 3d sublevel to achieve a completely filled 3d sublevel
Configurations and periodic table positions
- Elements are arranged in the periodic table in order of increasing atomic number divided into periods (rows) and groups (columns)
- Periods represent the principal quantum number (n) of the highest energy electrons each period corresponds to the filling of a new electron shell
- Groups contain elements with similar electron configurations in their outermost shell exhibiting similar chemical properties due to their valence electron configuration
- s-block elements (Groups 1 and 2) have valence electrons in the s subshell
- p-block elements (Groups 13 to 18) have valence electrons in the p subshell
- d-block elements (Groups 3 to 12) have valence electrons in the d subshell
- f-block elements (Lanthanides and actinides) have valence electrons in the f subshell
Key Terms to Review (28)
Actinides: Actinides are a series of 15 metallic elements in the periodic table from actinium (Ac) to lawrencium (Lr), with atomic numbers 89 to 103. They are known for being radioactive and having significant applications in nuclear energy.
Aufbau principle: The Aufbau principle states that electrons fill atomic orbitals of the lowest available energy levels before occupying higher levels. This helps determine electron configurations for atoms.
D-block elements: D-block elements are those elements in groups 3-12 of the periodic table, characterized by having their outermost electrons in a d orbital. They include transition metals known for their ability to form various oxidation states and complex compounds.
F-block elements: F-block elements are a set of elements found in the periodic table's f-block, which includes the lanthanides and actinides. These elements have electrons filling their f-orbitals and exhibit unique properties related to their electron configurations.
Hund’s rule: Hund's rule states that electrons will fill degenerate orbitals singly before pairing up. This minimizes electron-electron repulsions and results in the lowest energy configuration.
Lanthanides: Lanthanides are a series of 15 metallic elements from lanthanum (La) to lutetium (Lu) in the periodic table. They are known for their high magnetic susceptibility and luminescent properties.
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 underlies the structure of electron configurations and explains the unique placement of electrons within orbitals.
Quantum numbers: Quantum numbers are a set of numerical values that describe the unique quantum state of an electron in an atom. They provide information about the electron's energy, orbital shape, orbital orientation, and spin.
Valence shell: The valence shell is the outermost electron shell of an atom that contains electrons. Electrons in this shell are involved in chemical bonding and determine the chemical properties of the element.
Orbital: An orbital is a mathematical function that describes the wave-like behavior of an electron in an atom. It defines the probability distribution of an electron's position and energy within an atom. Orbitals are a fundamental concept in understanding the electronic structure of atoms, as they determine how electrons are arranged and behave within the atom.
Energy Levels: Energy levels refer to the discrete, quantized states that electrons can occupy within an atom. These energy levels represent the specific amounts of energy an electron can have as it orbits the nucleus of an atom. The concept of energy levels is fundamental to understanding the structure and behavior of atoms, as well as the evolution of atomic theory, the Bohr model, and the electronic structure of atoms.
F-block: The f-block, also known as the inner transition metals, is a group of elements in the periodic table that includes the lanthanides and actinides. These elements are characterized by the progressive filling of the 4f and 5f electron shells, respectively, which results in their unique electronic configurations and chemical properties.
S-block: The s-block is a group of elements in the periodic table that includes the alkali metals (group 1) and the alkaline earth metals (group 2). These elements are characterized by their high reactivity and the presence of s-orbital electrons in their valence shell.
Actinides: The actinides are a group of 15 radioactive elements in the periodic table, with atomic numbers ranging from 89 (actinium) to 103 (lawrencium). These elements are characterized by the filling of the 5f electron shell and are known for their complex electronic structures and radioactive properties.
Lanthanides: The lanthanides are a group of 15 elements in the periodic table, also known as the f-block or inner transition metals. They are characterized by the filling of the 4f electron shell and exhibit similar chemical properties due to their shared electronic configuration.
D-block: The d-block, also known as the transition metals, is a group of elements in the periodic table that are characterized by the filling of the 3d, 4d, and 5d electron shells. These elements exhibit unique chemical and physical properties that make them essential in various applications and industries.
P-block: The p-block, also known as the representative elements, is a group of elements in the periodic table that occupy the six rightmost columns. These elements are characterized by their valence electron configurations, where the outermost electron shells are being filled with p-orbitals.
Copper: Copper is a reddish-brown metallic element that is an essential mineral for human health and has numerous applications in various industries. It is a transition metal that exhibits unique chemical properties, making it an important component in many chemical processes and technological advancements.
Aufbau Principle: The Aufbau principle is a fundamental concept in quantum mechanics that describes the order in which electrons occupy the available energy levels or orbitals within an atom. It is a crucial principle in understanding the electronic structure of atoms and the formation of molecular orbitals.
Quantum Numbers: Quantum numbers are a set of discrete values that describe the state of an electron within an atom. They are fundamental to understanding the electronic structure of atoms and the behavior of electrons in electromagnetic fields.
Anomalous Configurations: Anomalous configurations refer to electron configurations that deviate from the expected order of filling the electron shells and subshells in atoms. These unusual arrangements of electrons can occur due to the complex interactions between the various energy levels and the stability of the electronic structure.
Electron Configurations: Electron configurations describe the arrangement of electrons within an atom's orbitals. This concept is fundamental to understanding the electronic structure of atoms and their chemical properties.
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, such as electrons, protons, and neutrons) can occupy the same quantum state simultaneously. This principle has significant implications for the electronic structure of atoms, the behavior of materials, and the understanding of molecular 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 is a crucial concept in understanding the electronic structure of atoms.
Hund's Rule: Hund's rule is a fundamental principle in quantum mechanics that describes the preferred electron configuration of an atom or molecule. It states that when electrons occupy degenerate orbitals, they will singly occupy these orbitals with parallel spins before pairing up, in order to minimize electron-electron repulsion and maximize the total spin angular momentum of the system.
Chromium: Chromium is a hard, silvery-gray transition metal that is essential for human health and plays a crucial role in the electronic structure of atoms. It is known for its ability to form a wide range of chemical compounds and its unique properties, which make it valuable in various industrial and technological applications.
Valence Electron: Valence electrons are the outermost electrons in an atom's electron configuration. They are the electrons involved in chemical bonding and participate in chemical reactions, determining an element's chemical properties and reactivity.
Subshell: A subshell is a division within the principal energy levels, or shells, of an atom's electron configuration. Subshells are further classified by their angular momentum quantum number, which determines the shape and orientation of the electron cloud around the nucleus.