Download Ch. 5 Notes: Electrons in Atoms Big Idea: The Atoms of each

Ch. 5 Notes: Electrons in Atoms
Big Idea: The Atoms of each element have a unique arrangement of electrons.
5.1: Light and Quantized Energy
Main Idea: Light, a form of electromagnetic radiation, has characteristics of both a wave and a particle.
Objectives:

Compare the wave and particle natures of light.

Define a quantum of energy, and explain how it is related to an energy change of matter.

Contrast continuous electromagnetic spectra and atomic emission spectra.
Review Vocabulary:
1. Radiation- the rays and particles- alpha particles, beta particles, and gamma rays- that are emitted by
radioactive material.
New Vocabulary:
1. Electromagnetic radiation
2. Wavelength
3. Frequency
4. Amplitude
5. Electromagnetic spectrum
6. Quantum
7. Planck’s constant
8. Photoelectric effect
9. Photon
10. Atomic emission spectrum
I.
Light and Quantized Energy
a. The Atom and Unanswered Questions
a. Rutherford’s model of the atom did not explain how the electrons are arranged in the
space around the nucleus.
b. Rutherford’s model of the atom did not explain why the negatively charged electrons
were not pulled into the positively charged nucleus.
c. Rutherford’s model did not account for the differences or similarities in chemical
behavior among various elements.
b. Elements emitted visible light when heated.
a. Element’s chemical behavior is related to the arrangement of the electrons in its atoms.
II.
The Wave Nature of Light
a. Electromagnetic radiation- a form of energy that exhibits wavelike behavior as it travels
through space.
1. EX: Visible light, X-rays, Microwaves
a. Characteristics of Waves
a. Wavelength ()- the shortest distance between equivalent points on a continuous wave.
i. Expressed in meters, centimeters, or nanometers.
b. Frequency (v)- the number of waves that pass a given point per second.
i. Expressed in Hertz (1 wave per second)
c. Amplitude- wave’s height from the origin to a crest, or from the origin to a trough.
d. All electromagnetic waves travel at a speed of 3.00 x 10 8 m/s in a vacuum.
i. Speed of light (c)
e. Electromagnetic Wave Relationship
i. c =  v
1. c = speed of light (3.00 x 10 8 m/s)
2. = wavelength (meters)
3. v = frequency (Hertz)
ii. Inverse relationship
b. Electromagnetic Spectrum
a. Sunlight (white light) contains a continuous range of wavelengths and frequencies.
b. Electromagnetic spectrum- includes all forms of electromagnetic radiation, with the only
differences in the types of radiation being their frequencies and wavelengths.
c. Energy of radiation increases with increasing frequency.
III.
The Particle Nature of Light
a. The Quantum Concept
a. When objects are heated, they emit glowing light.
1. As objects get hotter, they possess greater amounts of energy and emit different
colors of light.
2. Max Planck: Matter can gain or lose energy only in small, specific amounts called
quanta.
a. Quantum- the minimum amount of energy that can be gained or lost by
an atom.
3. Energy of a Quantum
a. E quantum = hv
i. E quantum = Energy (Joules)
ii. h = Planck’s constant = 6.626 x 10 -34 J.s
iii. v = frequency (Hertz)
b. Energy of radiation increases as the radiation’s frequency increases.
4. According to Planck’s theory, for a given frequency, matter can emit or absorb
energy only in whole-number multiples of hv.
b. The Photoelectric Effect
a. Electrons, called photoelectrons, are emitted from a metal’s surface when light of a
certain frequency, or higher than a certain frequency, shines on the surface.
c. Light’s Dual Nature
a. In 1905, Albert Einstein proposed a dual nature of light (wavelike and particle-like
properties).
1. Photon- a massless particle that carries a quantum of energy.
2. Energy of a Photon
a. E photon = hv
i. E photon = Energy (Joules)
ii. h = Planck’s constant = 6.626 x 10 -34 J.s
iii. v = frequency (Hertz)
IV.
Atomic Emission Spectra
a. The light of a neon sign is produced by passing electricity through a tube filled with neon gas.
Neon atoms in the tube absorb energy and become excited. These excited atoms return to
their stable state by emitting light to release that energy. If the light emitted by the neon is
passed through a glass prism, neon’s atomic emission spectrum is produced.
b. Atomic emission spectrum- the set of frequencies of the electromagnetic waves emitted by
atoms of the element.
a. Unique to each element and can be used to identify an element or determine whether
that element is part of an unknown compound.