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Electron Configurations. Quantum Mechanical Model of the Atom. The Quantum Mechanical Model is the current description of electrons in atoms. - does not describe the electron ’ s path around the nucleus The Quantum Mechanical Model is based on several ideas including:
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Quantum Mechanical Model of the Atom The Quantum Mechanical Model is the current description of electrons in atoms. - does not describe the electron’s path around the nucleus The Quantum Mechanical Model is based on several ideas including: Schrodinger wave equation (1926) treats electrons as waves. Heisenberg uncertainty principle (1927) states that it is impossible to know both the velocity and position of a particle at the same time.
Where do electrons “live”?A. Principal Energy Levels • Principal energy levelsn =1 to 7. (Row # on the periodic table) • The electron’s principal energy level is based on its location around the nucleus. • Electrons closer to the nucleus are at a lower energy level and have lower energy than those farther away from the nucleus
Energy levels in an atom’s electron are unequally spaced. The higher energy levels are closer together. Energy levels are like rungs of a ladder. You cannot be in between a rung
B. Atomic Orbitals An atomicorbital is a region of space in which there is a highprobability of finding an electron assigned letters s, p, d or f (smart people do fine) Energy sublevels correspond to a shape where the electron is likely to be found.
Energy Levels, Sublevels, and Orbitals Principal energy levels – n, assigned values 1-7 (Like floors in a hotel) Energy sublevels- s, p, d, f (Type of suite in a hotel) s sublevel – 1 orbital p sublevel – 3 orbitals d sublevel – 5 orbitals f sublevel – 7 orbitals Orbitals – Two electrons per orbital (Two people per room) (Orbitals are like the number of rooms in a suite)
Electron Configurations Electron configuration – the arrangement of electrons in an atom. Example Sodium (Na) – 1s22s22p63s1 Three rules determine electron configurations the Aufbau Principle, the Pauli Exclusion Principle Hund’s rule
The Aufbau Principle Each electron occupies the lowest energy orbital available Like filling the hotel from the bottom up
Aufbau Diagram Which has a lower energy level 4s or 3d orbitals?
Pauli Exclusion Principle A maximum of two electrons may occupy a single orbital Like only two people sharing one hotel room
Hund’s Rule If two or more orbitals of equal energy are available, electrons will occupy them singly with the same spin, before filling them in pairs with opposite spins A spin is denoted with an up or down arrow to fill orbitals This is like trying to find your own room in the same suite before having to share a room with someone else
Writing Electron Configurations Aufbau diagram for sodium (Na) which has 11 electrons Na electron configuration1s22s22p63s1
Exceptions to Electron Configurations Copper and chromium are exceptions to the Aufbau principle. Some configurations violate the Aufbau Principle because half-filled sublevels are not as stable as filled sublevels, but they are more stable than other configurations
Valence electrons Valence electrons are electrons in the outermost orbital For A group elements the group number corresponds to number of valence electrons. Electron-dot structures – Element’s symbol surrounded by dots representing the valence electrons 8A
