# Quantum Mechanical Model Electron Placement

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Quantum Mechanical Model Electron Placement

Electron basics Carries the negative charge of the atom
Has mass of amu (6/10000 mass of a proton) Located in region around nucleus Has a spin that creates a magnetic field Either spins clockwise (“up”) Or counterclockwise (“down”) Atoms are electrically neutral, therefore, the number of electrons = number of protons.

B.      Electron Placement 1.    Not Bohr Orbits Electrons rarely, if ever, orbit in neatly defined circles.

2. Orbitals = Regions of Probability
B.      Electron Placement 2.    Orbitals = Regions of Probability Where electrons are likely to be found Determined by electron density Area of high density = many electrons are there = Orbital! Area of low density = few electrons are there = Not Orbital!

2. Orbitals = Regions of Probability
Orbital Shapes: f – very complex shapes, with seven orbital orientations. (pictures don’t do this shape justice.) d - clover shaped, with four possible orientations in xy, yz, zx, and x2 – y2 planes; also one dumb-bell-with-ring shape, on z-axis. Five total orbital orientations. s - spherical shape, centered on nucleus p - dumb-bell shaped, with three possible orientations on x-, y- or z-axes. Dumb-bell “neck” centers on nucleus

B. Electron Placement 3. Energy Levels Energy level Sublevels n = 1 1s
As Bohr theorized, we believe electrons have certain levels of energy (level = n = 1, 2, 3, etc.) For each level of energy, there are sublevels of energy: Energy level Sublevels n = 1 1s n = 2 2s, 2p n = 3 3s, 3p, 3d n = 4 4s, 4p, 4d, 4f

3. Energy Levels Each level n has n sublevels
Each sublevel (s, p, d, f) corresponds to orbital shapes and orientations: Sublevel s contains one s orbital Sublevel p contains three p orbitals Sublevel d contains five d orbitals Sublevel f contains seven f orbitals

B.      Electron Placement 4.    Fitting electrons into place: Electron Configuration Aufbau Principle: Electrons will inhabit the lowest possible energy level and sublevel. Pauli Exclusion Principle: Each orbital holds a maximum of two electrons: one of each spin. Hund’s Rule: Electrons will spread themselves out in a sublevel so that a maximum number of unpaired electrons result If a sublevel were a bus, electrons wouldn’t share seats unless they had to.

Electron Configuration
Y 1s 2s 2p 3s 3p 4s 3d Fluorine: 9 protons, 9 electrons 1s2 2s2 2p5