Quantum Theory and the Atom

Bohr’s Model of the Atom ΔE = E higher-energy orbit – E lower-energy orbit = E photon = hv

Limitations of the Bohr Model The Bohr Model considers electrons to have both a known radius and orbit. Bohr model cannot account for spectral lines of larger atoms The Bohr Model is very limited in terms of size (larger atoms with more electrons) Although, the Bohr model laid the foundation for modern physics, it is fundamentally incorrect Instead of focusing on the arrangement of the orbitals, scientists began rethinking the way electrons move around the nucleus

Louis De Broglie Scientists at the time were aware of the dual particle-wave nature of photons De Broglie realized that if it was possible for waves to have particle like qualities, then it would also be possible for particles to have wave-like properties.

De Broglie Wave Equation

Heisenberg Uncertainty Principle German theoretical physicist (and notorious drug lord) Werner Heisenberg showed that it is impossible to pinpoint the exact location of a particle at any given moment Heisenberg pointed out that it is impossible to take measurements on a particle without disturbing it. Uncertainty Principle: It is fundamentally impossible to know precisely both the velocity and the position of a particle at the same time

Schrödinger Wave Equation In 1926 Austrian Physicist Erwin Schrödinger derived an equation that treated the Hydrogen atom’s electron as a wave The equation was not meant to represent a particle’s position, but rather a probability of its position at a certain time. Consider the equation below for the wave of an earthquake

Electron’s probable location The electron can be found in a three dimensional around the nucleus called the atomic orbital. The position of the electron can be random at any given moment, and since the electron moves so fast, the orbital can be thought of as a dense cloud Keep in mind this cloud has no definite boundary

Principle Quantum Number and Energy Levels Remember, the Bohr Model assigned principle quantum numbers to each energy level. The principle quantum number indicates the approximate size and energy of the atomic orbital Every orbital has a principal energy level. So, n=1 is the lowest energy level. Principal energy levels contain sublevels n=1 has 1 sublevel n=2 has 2 sublevels n=3 has 3 sublevels

Orbital Shapes

Principal Quantum Number (n) Sublevels (Types of orbitals) present Number of Orbitals Related to Sublevel Total Number of Orbitals Relating to Principal Energy Level (n 2 ) 1s11 2spsp spDspD spdfspdf Hydrogen’s First Four Principal Energy Levels