Chemistry - Unit 5: Light

Chemistry

light

a form of energy that travels in waves and requires no medium (i.e. it doesn’t move matter); also known as electromagnetic radiation due to its perpendicular electric and magnetic components; dual-nature form of energy that sometimes acts as a wave that extends into space and sometimes acts as a stream of continuous energy packets (called photons)

photons

the tiny energy packets of light that carry the quantized energy of a given wavelength

wavelength

the distance between consecutive peaks or troughs of a wave; typically measured in nanometers when dealing with light

mechanical wave

a wave that transfers energy by moving matter, or through a medium (e.g. sound, ocean, etc.)

frequency

a measure of how often something occurs; represents how often the peak (or trough) of a wave passes a given point; measured in units of Hertz (Hz) or inverse seconds (s-1)

continuous spectrum

produced when the light being split contains a range of wavelengths of light without any breaks; a rainbow is an example of a continuous spectrum, which is produced when the white light of the sun is separated into its component wavelengths

line spectrum

a spectrum that includes individual wavelengths (colors) of light separated by black sections; created when light that contains only a few wavelengths of light is separated

diffraction

the separation of light that results when light passes through a thin slit or is bent around a corner

refraction

Splitting of light when it passes through one medium to another, changing its speed and angle

white light

a mixture of all wavelengths of visible light

quantized

a system of non-continuous allowable energies; potential energy levels of the rungs of a ladder

quantum

“fixed amount”, the smallest quantity of energy that can be absorbed or released (emitted), the quantized energy of light is photons

shells

the quantized energy levels, circular paths that electrons travel around the nucleus

light absorption

absorbance of energy by electrons, electrons jump from a lower energy level to a higher energy level

light emission

when excited electrons return to their ground state and their potential energy is released in the form of light

spectrophotometry

analytical technique that uses light absorbance to determine the concentration of a solute in a solution

colorimetry

spectrophotometry for colored solutions only

Beer’s law (Beer-Lambert law)

light absorbance of a solution is directly proportional to the product of the solute concentration, the distance traveled by the light through the solution (pathlength), and a constant

concentration

the relative amount of solute per given amount of solvent or solution (it depends on the unit); molarity (mol solute/L sol’n) is the most common unit of concentration used by chemists

molarity

unit of concentration that represents the number of moles of solute in 1 liter of the solution