Synopsis of light and matter for the lay person

The aim of this lecture is to establish the basics of physics and chemistry that are important to the rest of the semester - no more. For some of you this will be new, for others, a maddeningly simplistic review. Still, by the end, we will all be on the same page. Courage.

Matter:

An element: A substance that connot be broken down into simpler substances by chemical means. Thus, hydrogen and oxygen are elements, but water, which can be broken down into hydrogen and oxygen, is not. (Note: don't be confused by radioactive decay. That is NOT a chemical process.)

The Atom: the smallest unit of an element that retains that element's physical and chemical properties.

Structure of atoms:

Chemistry: Atoms interact with one another chemically because of the behavior of electrons. An atom's behavior represents the equilibrium of two opposing forces:

Because of the first tendency, atoms ionize. Because of the second, they form chemical bonds with other atoms, yielding molecules of chemical compounds. Let's examine those in greater detail.


The Horsehead Nebula from Kwun Tong Government Secondary School
Ionization:

The periodic table of elements provides a convenient summary of the chemical behavior of the elements. (But hey, don't accuse me of not "teaching the controversy!")


Chemical Bonds: The tendency of atoms to remain electrically neutral accounts for the formation of chemical bonds. That is, atoms may ionize, but ions will associate with one another in such a way as to cancel out one another's charges.

Light


Electromagnetic spectrum from Wikipedia

Visible light is part of the electromagnetic spectrum that also includes radio, microwave, infrared, ultraviolet, X-ray, and gamma ray radiation. This radiation takes the form of particles, photons, whose propagation can be mathematically described as waves. They show these properties:

The speed of light (c) is always the same, regardless of its wavelength, when measured in a vacuum. It is 2.998 x 108 m/s.

The wavelength and frequency are related to the speed by:

c = λ ν

The energy of light is related to its wavelength:

E = hc / λ

where Planck's constant h is 6.626 x 10-34 J s.

Although variation along the electromagnetic spectrum is continuous, we break it up into distinct regions (Measurements in nanometers (nm) One nm = 1x10-9 m.):

Practical consequences:


Spectroscopy: Analysis of the distribution of wavelengths of light coming from an object - its spectrum - can be used to determine its composition, temperature, and velocity. This is because of fundamental connections between matter and light: