Atom and Ev Atoms, Energy, and the Heisenberg Uncertainty Principle Atoms, Energy, and the Heisenberg Uncertainty Principle By Lee Wignall.

Atom and Ev

Atom and Ev

Atoms,Energy,

and

the Heisenberg Uncertainty

Principle

Atoms,Energy,

and

the Heisenberg Uncertainty

Principle

By Lee Wignall

The idea that matter is made of small, indivisible “pieces” has been around for

thousands of years.

The word “atom” is derived from the Greek word “atomos”, meaning “that which cannot be

divided”.

Leucippus: Greek philosopher/scientist

Democritus: student of Leucippus and considered “Father of Modern Science”

Fast forward over 1000 years…

John Dalton

In 1808, John Dalton came up with four postulates of his “atomic theory.”

(there are actually five, but only the first four are well-known)

Fast forward 100 years…

J.J. Thomson

In 1906, Thomson created a current of negatively charged particles in a cathode-ray tube that were much smaller than an atom.

He called these tiny particles “corpuscles” and created the new model of the atom. Negatively charged “corpuscles” were spread around a positively charged sphere, like raisins in

plum pudding.

Plum pudding atomic model

2 years later…

In 1908, Ernest Rutherford fired alpha particles (protons) at gold atoms and discovered that the center of the atom is densely packed and positively charged.

Gold foil experiment

He called the center of the atom the nucleus and proposed that the negatively charged electrons orbit around the nucleus like planets.

5 years later…

In 1913, Neils Bohr introduced quantum mechanics into the atomic model.

He proposed the idea that electrons were only allowed to orbit the nucleus at certain energy levels. Instead of an infinite number of possible orbits, only certain orbits were allowed. (“quantizing the atom”)

Electrons could only jump to a higher energy orbit if they absorbed a photon

with enough energy.

Electrons jumping down energy levels would emit a photon with the exact energy difference between orbits.

The Electron Volt (Ev) The Electron Volt (Ev)

-13.6 Ev

-3.4 Ev

The energy of subatomic particles is measured in electron volts (Ev).

An electron absorbs a photon with enough energy to jump to the next highest energy level.

The Electron Volt (Ev) The Electron Volt (Ev)

-13.6 Ev

-3.4 Ev

The energy of subatomic particles is measured in electron volts (Ev).

An electron jumps down to a lower energy level and emits a photon with the energy difference.

The lowest “natural” energy state is the ground state.

Glow in the DarkGlow in the Dark

Electrons in the paint absorb energy from ambient light and jump to higher energy orbits.

However, this energetic state is unstable and as soon as the energy source (light) is removed, the electrons jump back down to their ground-state, emitting photons with energy equal to the difference between orbits.

Louis de BroglieLouis de Broglie

de Broglie proposed in 1924 that if light can act as both a particle and a wave, then shouldn’t all moving particles act as waves as well?

Matter waves: the more massive an object, the smaller the associated wavelength. Therefore, large objects have wavelengths that are WAY too short to be noticeable on any level.

13 years later…

In 1926, Erwin Schrodinger introduced probabilty into the structure of the atom.

Borrowing de Broglie’s idea that all matter exhibited wave-like properties, Schrodinger created an equation that describes the way a wave evolves.

The Schrodinger Wave Equation

?Don’t worry, I’ll break it

down for you.

This is “h-bar”, Planck’s constant (6.6 *10^-34 J*s) divided by 2 times pi. The mass of the particle being described.

Called the “del-squared operator”, this quantity describes how the wavefunction, , changes from one place to another.

The wavefunction: “psi”

Describes all the forces acting on the particle.“imaginary number”: it’s the square root of minus one.Describes how the wavefunction changes over time.

Applying the Schrodinger Equation to an Atom

Applying the Schrodinger Equation to an Atom

When you apply the Schrodinger Equation to an electron in an atom, you end up with a wavefunction that gives the probability of

finding the electron in any given location.

This computer analysis shows the results of the Schrodinger Equation under certain circumstances. You can clearly see the denser “cloud” where the probability of finding the electron is higher.

All the possible locations “smear” together to create an electron cloud.

Electron cloud

nucleus

Without direct observation, the position of the electron is given by the wavefunction--a probability wave that describes the chances of finding it at any given location.

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Electron cloud

nucleus

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But electrons are both a wave and a particle, and so we should be able to determine it’s position by direct observation (with high-tech equipment).

Without direct observation, the position of the electron is given by the wavefunction--a probability wave that describes the chances of finding it at any given location.

As soon as we make an observation about the precise location of the electron, we reduce the probability of finding it in any other location to zero, thereby “collapsing the wavefunction.”

Observed location of electron

Only upon observation does the electron begin to act as a particle. Just like with the double-slit experiment!

The Uncertainty PrincipleThe Uncertainty Principle

An interesting feature of the Schrodinger wave equation is the more precise you calculate the position of the particle, the less you can determine the momentum (and vice versa).

Werner HeisenbergThis is called the Heisenberg Uncertainty Principle. (formulated in 1927)

The uncertainty in the particle’s position.The uncertainty in the particle’s momentum.The combined uncertainty in both the position and momentum has to be greater than (or equal to) h-bar divided by two.

So, the more you know about position, the less you know about momentum!

http://www.youtube.com/watch?v=KT7xJ0tjB4A

Click below to begin youtube video on Heisenberg’s Uncertainty Principle.

I know it’s 1932 and I’m tardy to the party, but I just discovered the neutron.

I’m kind of a big deal.

James Chadwick

Heisenberg and Bohr, two heavyweights in atomic theory for their quantum contributions, immediately adopted the theory and used the neutron to explain small discrepancies in their experiments.