October 14, 2014

Atomic Spectroscopy and the Bohr Model of the Atom

October 14, 2014

Exploration 1:Using the spectroscope, look outside. DO NOT TRY TO LOOK AT THE SUN. Bad for your eyes.

What do you see?

October 14, 2014

Exploration 2:Using the spectroscope, we will now look at various gasses of elements.

What do you see?

October 14, 2014

Exploration 3: Flame TestFollowing the procedures demonstrated, you will test 4 different substances in a flame.

What do you see?

October 14, 2014

What is happening?

Work on POGIL to STOP sign on P.3.

October 14, 2014

What do you know about light now?

October 14, 2014

Light

• Light is a type of electromagnetic radiation that travels as a wave and can also act like a particle called a photon.> A photon is a discrete packet of light energy

Examples of EM radiation:• X-ray Gamma rays Radiowaves• Visible light UV Microwaves

October 14, 2014

Wavelength

• Wavelength: Distance between wave crests. Measured in (m or nm)

symbol

October 14, 2014

Frequency

• Frequency: How fast a wave oscillates. Number of wavelengths that pass through a given point per second. (Units in Hz or /s)

symbol

October 14, 2014

Wave Speed

• Wave speed: how fast wave is traveling through space. Measured in m/s.> Regardless of wavelength or frequency, all EM

radiation travels at 3.00 x 108 m/s (speed of light)

symbol c

http://micro.magnet.fsu.edu/primer/lightandcolor/speedoflight.html

October 14, 2014

There is a mathematical relationship between the wavelength and frequency of a wave.

• The longer the wavelength, the lower the frequency.• The shorter the wavelength, the higher the frequency.

=wavelength (m)speed of light

(m/s)

frequency (Hz)

October 14, 2014

h = Planck's constant

= 6.626 x 10-34 J*s

Energy of Light

• Light energy comes in discrete packets called photons> light energy is quantized: you can only have

discrete amounts of light energy.

Ephoton= h

If you substitute =wavelength (m)speed of light

(m/s)

frequency (Hz) Ephoton= h*c

October 14, 2014

Example 1:

• A red light has a wavelength of 660 nm. What is the frequency? (remember to convert nm to m first!)> What is the energy of the photon?

• A light has a frequency of 6.8 x 1015 Hz. What is the wavelength?> What is the energy of the photon?

October 14, 2014

Light Through a Prism

• When light is passed through a prism, the color components of light can be separated.

https://www.e-education.psu.edu/astro801/content/l3_p3.htmlhttp://climate.psu.edu/data/frost/frosttraining.php

October 14, 2014

Continuous Spectrum

• Continuous spectrum: Shows all of the wavelengths of light that are being emitted by white light.> Light separates into continuous array of colors.> White light is a mixture of all of the different

colors of light.

• long wavelength• low frequency• low energy

• short wavelength• high frequency• high energy ROY G BIV

October 14, 2014

October 14, 2014

Emission Spectrum

• Emission spectrum: shows the specific frequencies of light emitted by an excited atom.> Atoms have a unique emission spectrum. Can be

identified by the light they emit.

October 14, 2014

October 14, 2014

Bohr Model

• Scientists had a difficult time explaining emission spectra> Why were there specific lines of color instead of

all the colors?> Why were the colors always the same for a

specific element?

This guy had an idea!

October 14, 2014

*Finish POGIIL*

October 14, 2014

Bohr Model

• Niels Bohr developed model for the atom that explained the atomic spectra.> Electrons go around an atom's nucleus in circular

orbits.> Circular orbits are different distances from the

nucleus.> Energy of an electron depends on its distance

from the nucleus.

Planetary orbital model

October 14, 2014

Bohr Model

• When an atom absorbs a photon of light, it is absorbing energy.> Absorption of a photon: low potential energy

electron becomes high potential energy electron.> Emission of a photon: A high potential energy

electron loses some of its energy, electron moves closer to nucleus

October 14, 2014

Bohr Model

• Since light energy is quantized, the energy of an electron must also be quantized.> An electron can only have discrete amounts of

potential energy.> With in the atom, there are energy levels.

Electrons cannot be "inbetween" energy levels

October 14, 2014

Think about a staircase:

http://www.physics.ucla.edu/k-6connection/forwpsa.htm

Just like you can't stand in between the steps, an electron can only be in an energy level, not in between.

October 14, 2014

October 14, 2014

∆Eelectron = En-final – En-initial

• ∆Eelectron > 0 when increasing n• ∆Eelectron < 0 when decreasing n• |∆Eelectron| = Ephoton

Energy of an electron

En= -2.18 x 10-18 Jn2

n= principal quantum number

negative sign means energy of e- bound to nucleus is lower than if it were a free e-