Quantum TheoryQuantum Theory

Objectives:Objectives:Compare the particle to wave Compare the particle to wave model of lightmodel of lightAnalyze the path of the electronAnalyze the path of the electronContrast the spectraContrast the spectraIdentify the quantum numbers Identify the quantum numbers that lead to the locations of the that lead to the locations of the electronselectronsWrite electron configurations Write electron configurations andandDefine the parts of the Define the parts of the configuration such as the valenceconfiguration such as the valence

FactsFacts

So, we know what is in the nucleus.So, we know what is in the nucleus. Protons and neutronsProtons and neutrons Most of the mass of the atom lies hereMost of the mass of the atom lies here

How do the electrons exist outside How do the electrons exist outside the nucleus?the nucleus? How do electrons occupy the space How do electrons occupy the space

surrounding the nucleus?surrounding the nucleus? How do they avoid the laws of physics? How do they avoid the laws of physics?

(repulsion)(repulsion)

The electromagnetic spectrum The electromagnetic spectrum (above) illustrates the visible light (above) illustrates the visible light portion of electromagnetic radiation.portion of electromagnetic radiation.

What energy type comes after the What energy type comes after the violet?violet?

What energy type comes after the What energy type comes after the red?red?

Which one has the most energy? Which one has the most energy? Least?Least?

Fact Sheet 2Fact Sheet 2 Electromagnetic waves Electromagnetic waves

can be described by can be described by their wavelengths, their wavelengths, energy, and frequency. energy, and frequency.

All three of these All three of these things describe a things describe a different property of different property of light, yet they are light, yet they are related to each other related to each other mathematically. mathematically.

Wavelength is usually Wavelength is usually measured in meters measured in meters (m). (m).

Frequency is the Frequency is the number of cycles of a number of cycles of a wave to pass some wave to pass some point in a second. The point in a second. The units of frequency are units of frequency are thus cycles per second, thus cycles per second, or Hertz (Hz). or Hertz (Hz).

All light travels at the All light travels at the same speed, but each same speed, but each color has a different color has a different wavelength and wavelength and frequency. It is their frequency. It is their different wavelengths different wavelengths that cause the that cause the different colors of different colors of light to separate and light to separate and become visible when become visible when passing through a passing through a prism.prism.

Let’s analyze the wave:Let’s analyze the wave:

Waves in the electromagnetic spectrum vary in size from very Waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short long radio waves the size of buildings, to very short gamma-rays smaller than the size of the nucleus of an gamma-rays smaller than the size of the nucleus of an

atomatom

Illustration of frequency:Illustration of frequency:

Look at the illustration of the visible spectrum above. Can you guess which color has the longest wavelength?

Frequency vs. Frequency vs. WavelengthWavelength

Based on prior knowledge, just how Based on prior knowledge, just how do these two relate?do these two relate?

Why can we use these terms to Why can we use these terms to discuss anything on the discuss anything on the electromagnetic spectrum?electromagnetic spectrum?

Mathematical RelationMathematical Relation

Speed = Wavelength * Frequency

Materials:Materials: set of red, green and violet (purple) pencilsset of red, green and violet (purple) pencils manila folder meter stick or metric ruler manila folder meter stick or metric ruler  pair of scissors pair of scissors  4 books 4 books  watch with second hand watch with second hand  one strip of masking tape one strip of masking tape  extra pencilextra pencil

LAB: Obj: You will construct a simplified model of different light waves in order to determine a constant relationship between

wavelength and frequency.

We already know that light acts like a We already know that light acts like a wave, but did you know that sometimes it wave, but did you know that sometimes it acts like a particle? We call particles of acts like a particle? We call particles of light light photonsphotons. Low-energy photons, like . Low-energy photons, like radio photons, tend to behave more like radio photons, tend to behave more like waves, while higher energy photons (i.e. waves, while higher energy photons (i.e. X-rays) behave more like particles. That's X-rays) behave more like particles. That's another reason that we don't talk about X-another reason that we don't talk about X-ray waves very often. Instead we talk ray waves very often. Instead we talk about individual X-rays and their energies.about individual X-rays and their energies.

Atomic Emission SpectraAtomic Emission Spectra

When matter is heated, it gives off When matter is heated, it gives off light. For example, turning on an ordinary . For example, turning on an ordinary light bulb causes an electric current to bulb causes an electric current to flow through a metal filament which flow through a metal filament which heats the filament and produces the filament and produces light

The electrical The electrical energy absorbed by the absorbed by the filament excites the atoms' filament excites the atoms' electrons causing them to 'wiggle'. This absorbed causing them to 'wiggle'. This absorbed energy is eventually released from the is eventually released from the atoms in the form of in the form of light. .

Neon line spectraNeon line spectra

Bohr knew that when pure Bohr knew that when pure elements were were excited by excited by heat or electricity, they gave off or electricity, they gave off distinct colors rather than white distinct colors rather than white light. This . This phenomenon is most commonly seen in modern phenomenon is most commonly seen in modern day neon lights, tubes filled with gaseous day neon lights, tubes filled with gaseous elements (most commonly neon). When an (most commonly neon). When an electric current is passed through the gas, a electric current is passed through the gas, a distinct color (most commonly red) is given off distinct color (most commonly red) is given off by the by the element. When . When light from an excited from an excited element is passed through a prism, only specific is passed through a prism, only specific lines (or lines (or wavelengths) of ) of light can be seen. These can be seen. These lines of lines of light are called are called line spectraline spectra. .

                                                            

When an When an atom is excited, such as is excited, such as during heating, during heating, electrons can jump can jump to higher levels to higher levels

Bohr hypothesized that Bohr hypothesized that electrons occupy specific occupy specific energy levels levels. .

When the When the electrons fall back to fall back to lower lower energy levels, precise quanta levels, precise quanta of of energy are released as specific are released as specific wavelengths (lines) of (lines) of light. .

The comfy spot for an electron is on The comfy spot for an electron is on the the ground stateground state which is the lowest which is the lowest energy level in the atomenergy level in the atom

Key to Bohr's theory was the fact Key to Bohr's theory was the fact that the that the electron could only 'jump' could only 'jump' and 'fall' to precise energy levels, and 'fall' to precise energy levels, thus emitting a limited spectrum of thus emitting a limited spectrum of light. These pockets of energy are light. These pockets of energy are called “quanta”.called “quanta”.

Bohr also predicted that those levels Bohr also predicted that those levels had limits to the number of electrons had limits to the number of electrons each could hold. each could hold.

This leads us to the Quantum TheoryThis leads us to the Quantum Theory