Chemistry 12-5

• Aim: Explain energy changes of electrons as they move from the nucleus

• Do Now: Contemplate 2 things to be thankful for.

• Which electron has more energy- one in n=3 or n=6?

HW:

• Complete Firework reading & questions for Friday 12/7

• Lab 7 due Friday 12/7

Electrons & Energy

1- Main features of Bohr Model

• Atom has dense positively charged nucleus

• Electrons are in fixed paths around the nucleus

• Electrons have a specific amount of energy (quantized)

Problems with Bohr Model• When viewing emission spectra of Hydrogen (which has one

electron) the bright line spectra fits his model that an electron has a fixed path.

Kelter, Carr, Scott, Chemistry A Wolrd of Choices 1999, page 76

Bohr’s Experiment

BUT with more than 1 electron…

• Bohr’s model no longer fits- bright line spectra of various wavelengths emerge, leading one to believe electrons do not have FIXED positions but rather MOVE AROUND within and about orbitals.

1- Orbitals

• Region of space about nucleus with highest probability of finding an electron.

2- Wave mechanical model • Electrons do not orbit the nucleus in

definite fixed pathways.• Electrons are in orbitals– regions where

electrons are found- not fixed distances• Electrons have distinct amounts of energy

Venn Diagram of Bohr vs Wave mechanical Model

• Take what you learned in last few slides and reading from text and passage to create a venn diagram of these 2 atomic models.

Bohr

Wave mechanical

both

2-Potential Energy and Distance from nucleus

• As the distance from the nucleus increases, potential energy of an electron increases.

• WHY?

• The energy to get further from the nucleus increases, so an electron occupying that space will have more PE.

3- Ground state & Excited state Light• When all electrons are in the lowest possible energy state, an atom

is in the ground state.

• If the right amount of energy is absorbed by an electron, it can “jump” to a higher energy level. This is an unstable, momentary condition called the excited state.– photons (discrete bundles of energy)

ENERGY (HEAT, LIGHT,ELEC., ETC.)

Ex:

Ex:

When the electron falls back to a lower energy level, the atom releases the energy that it absorbed as light.

4- The amount of energy has to be just right (this is the whole “quantization” concept again).

The colors of light that atoms produce from this process is called the emission spectrum.

EMITTEDLIGHTEx:

http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/linesp16.swf

http://einstein.byu.edu/~masong/htmstuff/Absorb2.html

Animations to explain emission spectra and electron movement

Humor

Question:Question: Why does hamburger have lower energy than steak?

Answer:Answer: Because it’s in the ground state.

5 Energy & Frequency of a photon or quantum

• AS FREQUENCY INCREASES, ENERGY INCREASES

6 Frequency & wavelength of a photon or quantum

• AS FREQUENCY INCREASES, WAVELENGTH DECREASES

5,6: The Electromagnetic Spectrum

AM radio

Short waveradio

Television channels

FM radio

RadarMicrowave

Radio Waves Gamma Rays

X- Raysinfrared

Increasing photon energy

Increasing frequency

Decreasing wavelength

Red Orange Yellow Green Blue Indigo Violet

UV Rays

Visible

Light

R O Y G B I V

HIGH

ENERGY

LOW

ENERGY

7 SOURCE of bright line spectra

• Excitation of an electron, returning to GROUND state, energy (light) emitted in a particular wavelength and frequency due to where it is moving from (energy level n to ground state energy level n)

Copyright © 2006 Pearson Benjamin Cummings. All rights reserved.

Objectives

8, 9, 10

Flame test LAB

Flame Tests for Certain Metals

BORAX BEAD TESTS FOR CERTAIN METALS(All beads formed in the oxidizing flame)