Chapter 4 – Arrangement of Electrons in Atoms
Section 1: The Development of a New Atomic Model
Objectives:
• Be able to define: electromagnetic radiation, electromagnetic spectrum, wavelength, amplitude, frequency, photoelectric effect, quantum (pl. quanta), photon, ground state, excited state, line emission spectrum, continuous spectrum, energy level.
• Be able to explain the mathematical relationship between speed, wavelength, and frequency of a wave.
• Be able to describe what is meant by the wave-particle duality of light.
• Be able to discuss how the photoelectric effect and the line emission spectrum of hydrogen lead to the development of the atomic model.
• Be able to describe the Bohr model of the atom
A. Waves
• A ______is a method of transferring energy. This transfer does not require matter as a medium. Some waves travel through matter (sound, water waves, etc.). Some waves do not require matter and can travel through empty space (light).
• Waves can be described by their wavelength, amplitude, and frequency.
- A ______is the highest point on a wave.
- A trough is the ______point on a wave.
- Wavelength is simply the ______of a wave. It is the distance between two crests or two troughs. (Measured in m, mm, or nm.)
- ______is simply the height of a wave. It is the distance between the crest and trough of a wave. Amplitude is measured in units of distance.
- Frequency is the number of waves passing a given point in a given time. It describes the energy of a wave: the ______the frequency, the ______the energy of that wave. (Frequency is measured in hertz or cycles per second or vibrations per second or 1/sec or sec-1 - they all mean the same thing.)
• As the ______increases, frequency ______. This is called an inverse relationship.
• Wavelength and amplitude give waves their distinctive properties. For example, the loudness of a sound wave is its amplitude; the color of visible light is its ______.
• Electromagnetic waves do not require a medium or matter in order to travel. Light is an example.
B. Properties of Light - Wave Description of Light
• Light is an electromagnetic wave.
• Visible light is a small part of the electromagnetic spectrum that humans are able to see.
• Red has a ______wavelength than violet.
• The electromagnetic spectrum consists of different kinds of light of different wavelengths.
• ______light is light consisting of all colors of visible light. These colors are visible in a rainbow or through a prism.
• Frequency and wavelength are mathematically related to each other.
c = λν
Variable / Represents / Measured inPractice
1. What is the frequency of green light, which has a wavelength of 4.90x10-7 m?
2. An X-ray has a wavelength of 1.15x10-10 m. What is its frequency?
3. What is the wavelength of an electromagnetic wave that has a frequency of 78x106 Hz?
4. A popular radio station broadcasts with a frequency of 94.7 MHz. What is the wavelength of the broadcast? (1 MHz = 106 Hz)
5. What is the speed of an electromagnetic wave that has a frequency of 78x106 Hz?
6. A popular radio station broadcasts with a frequency of 94.7 MHz. What is the wavelength of the broadcast? (1 MHz = 106 Hz)
C. Photoelectric Effect
• In the early 1900s, scientists studied experiments that could ____ be explained by the wave ______of light.
• The photoelectric effect—The emission of ______from a metal when ______shines on the metal.
• For a given metal, no electrons were emitted if the light’s frequency was ______a certain minimum.
• Remember—light is ______.
• Max ______studied emission of light by _____ objects (completely absorb all radiantenergyfalling upon it, reaches some equilibrium temperature, and then re-emits that energy as quickly as it absorbs it).
• Proposed that hot objects do _____ emit EM energy continuously, but in small, specific packets called ______.
• A quantum is the ______quantity of ______that can be ______or ______by an atom.
E = hν is the formula that resulted.
D. Emission Spectra
· If an object becomes ______enough it will begin to emit ______.
· Max Planck suggested that hot objects emit light in specific amounts called ______(sing. quantum).
· h=6.626 x 10-34J s is the constant that comes from the work of Max Planck preformed in 1900 using blackbody radiation. There were discrete values of energy that differed by this constant.
· In other words, all energy is a multiple of this constant multiplied by the ______of the wave of light.
· Energy is therefore quantized, it is always a multiple of a single packet of ______.
· Planck showed the relationship between a quantum of energy and the frequency of the radiation.
Variable / Represents / Measured in / Variable / Represents / Measured inCalculating the energy of a photon
What is the energy of each of the following types of radiation?
1. 6.32x1020 s-1
2. 9.50x1013 Hz
3. 1.05x1016 s-1
4. Calculate the energy of a photon with a wavelength of 713 nm.
5. Calculate the energy of a photon with a frequency of 8.12*1016 s-1
E. Wave-Particle Duality
• Einstein later said that light had a dual nature – it behaved as both a particle and a wave.
• Each particle of light, Einstein said, carries a particular quantum of energy. Einstein called the “particles” of light ______, which had zero mass and carried a quantum of energy. The energy is described as:
• Einstein explained photoelectric effect by saying in order for an electron to be ejected from a metal, the photon striking it must have enough ______to eject it. Different metals have stronger attraction for their electrons than other. Therefore, some must absorb ______energy than others to ______electrons.
• The lowest energy state of an atom is called its ______state.
• When a current is passed through a gas at low pressure, the atoms become “excited.” Atoms in an excited state have a higher ______l energy than their ground state. An “excited” atom will return to its ground state by ______energy in the form of electromagnetic radiation.
F. Hydrogen-Atom-Emission- Line Spectra
• Elements will emit radiation of certain ______. This reflects the energy states of its electrons and is called a bright-line or emission spectrum. The emission spectrum of an element is like its “______”.
G. Bohr Model of Hydrogen Atom - Energy Levels
• Studying the emission spectrum of hydrogen lead Niels Bohr to the idea of ______. The spectrum Bohr and others observed was the result of excited electrons releasing photons as they returned to their ground states. The difference in the energy of photons was reflected in the different frequencies of light they observed.