5.2 and 5.3

Bohr vs the quantum mechanical model of the atom

5.2 and 5.3: Bohr and the quantum mechanical model

• Compare the Bohr and quantum mechanical models of the atom.

atom: the smallest particle of an element that retains all the properties of that element, is composed of electrons, protons, and neutrons.

• Explain the impact of de Broglie's wave article duality and the Heisenberg uncertainty principle on the current view of electrons in atoms.

• Identify the relationships among a hydrogen atom's energy levels, sublevels, and atomic orbitals.

Section 5.2 Quantum Theory and the Atom (cont.)

ground state

quantum number

de Broglie equation

Heisenberg uncertainty principle

Wavelike properties of electrons help relate atomic emission spectra, energy states of atoms, and atomic orbitals.

quantum mechanical model of the atom

atomic orbital

principal quantum number

principal energy level

energy sublevel

Review: Electrons (ground state and excited state)

So why did we get lines in the spectroscope?

• Niels Bohr (1885 – 1962)

• Worked with Rutherford

• Model of the hydrogen atom: the single electron of the hydrogen atom can circle the nucleus only in allowed paths called orbits

• Lowest energy = closest orbit to the nucleus

Bohr model of the atom

Bohr's Model of the Atom (cont.)

• Bohr suggested that an electron moves around the nucleus only in certain allowed circular orbits.

Bohr's Model of Hydrogen

Bohr's Model of the Atom (cont.)

• Each orbit was given a number, called the quantum number.

Importance of Bohr Model

• Using charge and mass of an electron and Planck’s constant (E=hν)

• Calculated the energies that an electron should have in the orbits.

• Compare calculationg to the line spectrum

• The calculations were correct

• The energy that Bohr model said an electron should have, was the same energy that the colored lines produced from the bright line spectrum

Problem with Bohr Model

• His mathematics only applied to the Hydrogen atom

Bohr Model of the Atom

• Bohr: - Orbit:

- electrons were treated as:

– correctly predicted line spectrum for __________, but could not for any other element

What to do now ??

• Bohr treated electrons like particles

• 1924: Louis de Broglie noticed that the spectrum lines could be explained by wave properties

• Example: waves confined in a space have only certain frequencies.

The Quantum Mechanical Model of the Atom (

• The figure illustrates that electrons orbit the nucleus only in whole-number wavelengths.

The Quantum Mechanical Model of the Atom (cont.)

• The de Broglie equation predicts that all moving particles have wave characteristics.

represents wavelengthsh is Planck's constant.m represents mass of the particle. represents frequency.

Heisenberg Uncertainty Principle

• The Heisenberg uncertainty principle states that it is fundamentally impossible to know precisely both the velocity and position of an electron at the same time.

• The only quantity that can be known is the probability for an electron to occupy a certain region around the nucleus.

Heisenberg Uncertainty Principle

• To see something, light must hit the object, bounce off it, and come back to our eye

• When light hits an electron, it makes it move because the electron is so small.

• By the time the reflected light gets back to our eye, the electron is no longer where it was.

The Quantum Mechanical Model of the Atom

• Using de Broglie’s and Heisenburg’s thoughts

• Schrödinger treated electrons as waves in a model called the quantum mechanical model of the atom.

• Schrödinger’s equation applied equally well to elements other than hydrogen.

Erwin Schrödinger, 1926

• Who has worked with the sin and cosine curve?

• Basically, he applied a wave formula (like sin or cosine) to the properties of the electrons– Worked for all atoms– Create electron orbitals instead of orbits– Can not pinpoint the location of the electron

The Quantum Mechanical Model of the Atom

• The wave function predicts a three-dimensional region around the nucleus called the atomic orbital.

Orbitals

Three dimensional region about the nucleus in which a particular electron can be located

Hydrogen Atomic Orbitals (cont.)

• Each energy sublevel relates to orbitals of different shape.

Schrodinger

• Orbitals - Mathematical representations of where electrons could be (Not specific)

• Can not ………._______________

• Treated electrons as _________

Result of Schrodinger

• Quantum Theory– Mathematically describes the wave properties

of electrons

– Creates orbitals which when added together, look like an electron cloud