Light and Quantized Energy

COOKES Light, a form of electromagnetic radiation, has characteristics of both a wave and a particle. 

Real-World Reading Link Have you ever come inside on a cold day, headed for the kitchen, and popped a cold snack into the microwave oven When the microwaves reached your snack, small packets of energy warmed it in practically no time at all. 

After discovering three subatomic particles in the early 1900s, scientists continued their quest to understand atomic structure and the arrangement of electrons within atoms. 

For example, consider the elements lithium, sodium, and potassium, which are found in different periods on the periodic table but have similar chemical behaviors. All three elements appear metallic in nature, and their atoms react vigorously with water to liberate hydrogen gas. 

In the early 1900s, scientists began to unravel the puzzle of chemical behavior. They observed that certain elements emitted visible light when heated in a flame. Analysis of the emitted light revealed that an element s chemical behavior is related to the arrangement of the electrons in its atoms. To understand this relationship and the nature of atomic structure, it will be helpful to first understand the nature of light. 

Although three suhatomic particles had heen discovered hy the early-1900s, the quest to understand the atom and its structure had really just begun. That quest continues in this chapter, as scientists pursued an understanding of how electrons were arranged within atoms. Perform the DISCOVERY LAB on this page to better understand the difficulties scientists faced in researching the unseen atom. 

As you learned in Chapter 4, Rutherford proposed that all of an atom s positive charge and virtually all of its mass are concentrated in a nucleus that is surrounded by fast-moving electrons. Although his nuclear model was a major scientific development, it lacked detail about how electrons occupy the space surrounding the nucleus. In this chapter, you will learn how electrons are arranged in an atom and how that arrangement plays a role in chemical behavior. 

Many scientists in the early twentieth century found Rutherford s nuclear atomic model to be fundamentally incomplete. To physicists, the model did not explain how the atom s electrons are arranged in the space around the nucleus. Nor did it address the question of why the negatively charged electrons are not pulled into the atom s positively charged nucleus. Chemists found Rutherford s nuclear model lacking because it did not begin to account for the differences in chemical behavior among the various elements. 

The amplitude of a wave is the wave s height from the origin to a crest, or from the origin to a trough. To learn how lightwaves are able to form powerful laser beams, read the How It Works at the end of this chapter. 

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Quasiclassical calculations are similar to classical trajectory calculations with the addition of terms to account for quantum effects. The inclusion of tunneling and quantized energy levels improves the accuracy of results for light atoms, such as hydrogen transfer, and lower-temperature reactions. 

Photoelectric effect The effect produced when electromagnetic radiation knocks electrons out of a metal. Einstein used this phenomenon to show that light was quantized and came in energy packets called photons. 

The model of metal-ammonia solutions that has emerged is based on ionization of the metal atoms to produce metal ions and electrons that are both solvated. The solvated electron is believed to reside in a cavity in ammonia, and thus it may behave as a particle in a three-dimensional box with quantized energy levels. Transitions between the energy levels may give rise to absorption of light and thereby cause the solutions to be colored. The dissolution process can be represented as... 

A more particle-oriented consideration of light shows that light is quantized and is emitted, transmitted, and absorbed in discrete units, so-called photons or quanta. The energy E of a photon or quantum (the unit of light on a molecular level) is given by ... 

A derived quantity is the wave number v, which is the reciprocal of X and specifies the number of wavelengths per unit distance (cm-1). The energy contained in light is quantized. A quantum of energy A Ex is one photon. Mathematically, this is defined as... 

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