River Dell Regional High School
Unit 3 – Electron ConfigurationsPart C: Quantum Mechanical Model
Background
Problem With the Bohr Model – Why andhow could the electron in hydrogen orbit inonly a small number of allowed paths?
Solving the Problem
1. Louis de Broglie – electrons have a
dual nature - they can act like
particles or waves !!!
Cathode Ray Tube Experiment(by JJ Thomson):
•Electrons travel at highspeed.
•Electrons have fixed mass.
All important attributes for particles.
Duality of Electrons
Duality of Electrons
Electron beam behaves like waves.
Heisenberg Uncertainty Principle
How can police tell the speed of a moving vehicle?
Heisenberg Uncertainty Principle
How can we tell the speed of a moving electron?
MovingElectron
Photon
Before
Electron ChangesVelocity
Photonchangeswavelength
After
Heisenberg Uncertainty Principle
Werner Heisenberg
1901-1976
Both the velocity andposition of a particle(electron) can not bemeasured at the same time.
Quantum Mechanical Model
Schrodinger – developedequations that treat electrons inatoms like waves.
•describe the shapes of theorbitals in which electronshave a high probability ofbeing found.
•quantum theory –mathematical explanation forthe wave properties ofelectrons that apply to allatoms.
Erwin Schrodinger
1887-1961
Quantum Mechanical Model
The nucleus is found insidea blurry “electron cloud”
A area where there is achance of finding anelectron
Principles of the Quantum Model
1.Electrons act like waves and particles.
2.Probability of an electron being foundat various distances from the nucleus.
3.orbitals – a 3-D region about thenucleus where a specific electron maybe found.
Principles of the Quantum Model
4.Electrons have greater energy as their distancefrom the nucleus increases.
5.Energies of orbitals are quantized within mainenergy levels.
6.The exact location of electrons can not bepinpointed – they are found in regions of highprobability called orbitals or electron clouds.
Similarities -Bohr and Quantum Model
1.The closer the orbital to the nucleus the lower theenergy.
2.To move from a lower to a higher level the energyabsorbed must be equal to the difference betweenthe levels.
3.When e- drops from a higher to lower levelelectromagnetic radiation is emitted equal to thedifference in energy levels.
4.The most probable location of the e- is a distanceequal to the lowest energy level.
Quantum Mechanical Model
•According to Schrödinger’s calculations, fourquantum numbers are needed to fully resolve thewave function mathematically for each electron inany given atom.
•Meaning – there is a unique set of four quantumnumbers to fully describe the behavior of anelectron.
Four Quantum Numbers
A.Principal Quantum Number (n)
main energy level
B. Orbital Quantum Number (l)
shape of orbital (s, p, d, f)
C. Magnetic Quantum Number (m)
orientation of orbital about the nucleus
D. Spin Quantum Number (s)
indicates clockwise or counter-clockwise spin of the electron(+½ or –½)
Summary
•Wave and particle duality of electrons.
•Heisenberg Uncertainty Principle.
•Schrodinger’s Quantum Mechanical Model of Atoms.