chapter 5: electrons in atoms. why focus on electrons? scientists wanted to know why certain...

Chapter 5: Electrons in Atoms

Why focus on electrons?Scientists wanted to know why certain

elements behaved similarly to some elements and differently to othersReactivityWhen heated with a flame

Light as WavesVisible light is a type of electromagnetic

radiation

electromagnetic radiation - a form of energy that exhibits wavelike behavior as it travels through space

Wave Diagram

http://www.bing.com/images/search?q=diagram+of+a+wave&qpvt=diagram+of+a+wave&FORM=IGRE&adlt=strict#view=detail&id=0E35D2E3DCCE58065D42744F87E2F1E50CDF5CE8&selectedIndex=3

Frequency (υ/f) - number of waves per second

- in hertz (Hz) or s-1 or

Wavelength (λ) - distance between corresponding parts on consecutive waves

- in meters (m)

Speed of light (c)

- 3.00 x 108 m/s

Electromagnetic Spectrum

Raging Martians Invaded Venus Using X-Ray Guns

LOW

ENERGY

HIGH

ENERGY

Frequency and wavelength are INVERSELY related

- as one goes up, the other goes down

c: speed of light (3.00 108 m/s): wavelength (m, nm, etc.)f: frequency (Hz)

c = f

What is the frequency of light that has a wavelength of 680. nm?

What is the wavelength of light with a frequency of 4.27 x1018 hertz?

Turn to your partner and summarize…State the relationship between the energy and

frequency of electromagnetic radiation.

Answer: frequency and energy are directly related, when one goes up, the other goes up, too

What are the only differences between the types of electromagnetic radiation on the electromagnetic spectrum?

Answer: frequencies and wavelengths of the waves

Light as ParticlesIn the early 1900’s, German physicist Max

Planck was trying to understand why some substances change color when heated.

What Max thoughtAs the substance is heated, its energy changes in

specific amounts called quanta

Quantum: the minimum amount of energy that can be gained or lost by an atom

The amount of energy that can be emitted by a substance is directly proportional to the frequency of the radiation given off.

If something is heated, the energy is increased and different frequencies of light are given off (different colors).

Ground state: the lowest allowed energy state of an atom or other particle

http://www.michaelbrown.org/HTML/Quantum.htm

Einstein’s ContributionObserved the photoelectric effect

Concluded - light has properties of both waves and particles

“wave-particle duality”

Photon - particle of light that carries a quantum of energy

C. Johannesson

The Photoelectric Effect

Electrons (called photoelectrons) are emitted from a metals surface when light of a certain frequency shines on the surface

Energy of light is:

- directly related to the frequency of the light

- inversely related to the wavelength.

- As frequency , energy

- As wavelength , energy

Energy has units of Joules (J)

h = Planck’s constant = 6.626 x 10-34 J. s E = hf

A photon has an energy of 1.23 x10-16 J. What is the frequency and wavelength of the photon?

So what does light have to do with chemistry?You can identify an element by the color of

light it gives off when heated…

How is light given off?

When atoms absorb energy (for example, from a flame), electrons become excited and temporarily get into a higher energy level

When they drop back down to their ground state, energy is released in the form of light

Atomic emission spectrum: the set of frequencies of the electromagnetic spectrum that consists of several individual lines of color corresponding to the frequencies of the radiation emitted by atoms of the element