Bohr model and Quantum Numbers October 28, 2014

Bohr’s Model Why don’t the electrons fall into the nucleus? Move like planets around the sun. In circular orbits at different levels. Amounts of energy separate one level from another. When electrons are hit with energy (flame, heat) they jump to a different level.

Bohr’s Model Nucleus Nucleus Electron Electron Orbit Orbit Energy Levels Energy Levels

Bohr postulated that: Fixed energy related to the orbit Electrons cannot exist between orbits The higher the energy level, the further it is away from the nucleus An atom with maximum number of electrons in the outermost orbital energy level is stable (unreactive)

} Fifth Fourth Increasing energy Third Second First Further away from the nucleus means more energy. There is no “in between” energy Energy Levels n= 1,2,3,4,5,6,7 Fifth Fourth Third Increasing energy Second First

How did he develop his theory? He used mathematics to explain the visible spectrum of hydrogen gas http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/linesp16.swf

The line spectrum electricity passed through a gaseous element emits light at a certain wavelength Can be seen when passed through a prism Every gas has a unique pattern (color)

Line spectrum of various elements Helium Carbon

The Quantum Mechanical Model Energy is quantized. It comes in chunks. A quantum is the amount of energy needed to move from one energy level to another. Since the energy of an atom is never “in between” there must be a quantum leap in energy. Schrödinger derived an equation that described the energy and position of the electrons in an atom

Atomic Orbitals Principal Quantum Number (n) = the energy level of the electron. Within each energy level the complex math of Schrödinger's equation describes several shapes. These are called atomic orbitals Regions where there is a high probability of finding an electron

Sublevels OF ENERGY s orbitals (sphere) p orbitals (dumbbell) d orbitals (5 different shapes) f orbitals (hard to visualize)

Sublevels, Orbital and number of electrons SUBLEVEL NUMBER OF ORBITALS S 1 p 3 d 5 f 7 To determine the number of electrons in a sublevel, we use the formula 2n2 where “n” energy level that is outside of the nucleus.

S orbitals 1 s orbital for every energy level 1s 2s 3s Spherical shaped Each s orbital can hold 2 electrons Called the 1s, 2s, 3s, etc.. orbitals

P orbitals Start at the second energy level 3 different directions 3 different shapes Each orbital can hold 2 electrons

The p Sublevel has 3 p orbitals

The D sublevel contains 5 D orbitals The D sublevel starts in the 3rd energy level 5 different shapes (orbitals) Each orbital can hold 2 electrons

The F sublevel has 7 F orbitals The F sublevel starts in the fourth energy level The F sublevel has seven different shapes (orbitals) 2 electrons per orbital

Summary Starts at energy level

Electron Configurations The way electrons are arranged in atoms. Aufbau principle- electrons enter the lowest energy first. This causes difficulties because of the overlap of orbitals of different energies. Pauli Exclusion Principle- at most 2 electrons per orbital - different spins

Electron Configurations First Energy Level only s sublevel (1 s orbital) only 2 electrons 1s2 Second Energy Level s and p sublevels (s and p orbitals are available) 2 in s, 6 in p 2s22p6 8 total electrons

Third energy level s, p, and d orbitals 2 in s, 6 in p, and 10 in d 3s23p63d10 18 total electrons Fourth energy level s,p,d, and f orbitals 2 in s, 6 in p, 10 in d, and 14 in f 4s24p64d104f14 32 total electrons

Great site to practice and instantly see results for electron configuration.