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CHARACTERISTICS OF ATOMS ATOMS CONTAIN A POSITIVELY-CHARGED NUCLEUS SURROUNDED BY NEGATIVELY CHARGED ELECTRONS. IN A NEUTRAL ATOM, THE NUMBER OF PROTONS AND ELECTRONS IS EQUAL. MOST OF THE ATOM IS EMPTY SPACE. ATOMS OF DIFFERENT ELEMENTS HAVE DIFFERENT PHYSICAL AND CHEMICAL PROPERTIES. ATOMS CAN COMBINE WITH ONE ANOTHER TO MAKE MOLECULES.

LIGHT ACTING AS A WAVE IS CHARACTERIZED BY: CHARACTERISTICSYMBOLUNITDEFINITION WAVELENGTH nmthe distance between wave crests FREQUENCY Hz or sec -1 The number of wave crests that pass a reference point in one second AMPLITUDEAHeight of the wave (number of photons)

THE ELECTROMAGNETIC SPECTRUM IS A RANGE OF ALL THE TYPES OF LIGHT THAT EXIST ARRANGED BY WAVELENGTH OR FREQUENCY. THIS INCLUDES GAMMA RAYS, X-RAYS, UV, VISIBLE, INFRARED, MICROWAVES, AND RADIO WAVES. WHITE LIGHT IS A COMBINATION OF ALL THE COLORS OF LIGHT IN THE VISIBLE SPECTRUM (400 TO 700 nm). WE CAN ONLY SEE VISIBLE LIGHT.

EACH WAVELENGTH OF LIGHT IN THE VISIBLE SPECTRUM IS ASSOCIATED WITH A COLOR. THE COLORS ARE: RED, ORANGE, YELLOW, GREEN, BLUE, INDIGO, VIOLET. ROY G. BIV

LIGHT IS A FORM OF ENERGY, AND THE ENERGY PER PHOTON IS INVERSELY RELATED TO WAVELENGTH. E = hC/  = h WHERE h = Planck’s constant C = speed of light = wavelength  = frequency AS THE WAVELENGTH INCREASES, THE FREQUENCY DECREASES AND THE ENERGY PER PHOTON DECREASES.

LIGHT HAS BOTH WAVE AND PARTICLE PROPERTIES. ONE WAY THE PARTICLE PROPERTIES CAN BE DEMONSTRATED IS THROUGH THE PHOTOELECTRIC EFFECT. PHOTOELECTRIC EFFECT – LIGHT WITH ENOUGH ENERGY CAN KNOCK ELECTRONS FROM THE SURFACE OF A METAL. E KE = E PHOTON – E BINDING WHERE E PHOTON = ENERGY OF PHOTON E BINDING = BINDING ENERGY OF ELECTRON E KE = KINETIC ENERGY OF FREE ELECTRON

THE LOWEST ENERGY STATE THAT AN ELECTRON CAN OCCUPY IN AN ATOM IS CALLED THE GROUND STATE. A HIGHER ENERGY STATE IS CALLED THE EXCITED STATE. ENERGY MUST BE ABSORBED BY AN ATOM TO MOVE AN ELECTRON FROM THE GROUND STATE TO AN EXCITED STATE. THIS ENERGY CAN COME FROM THERMAL ENERGY (HEAT), CHEMICAL ENERGY, OR LIGHT ENERGY.

WHEN AN ATOM RETURNS FROM AN EXCITED STATE TO LOWER ENERGY STATES OR TO THE GROUND STATE, THAT EXACT AMOUNT ENERGY MUST BE GIVEN OFF, EITHER AS LIGHT OR HEAT. ENERGY LEVELS IN AN ATOM ARE QUANTIZED, THAT IS, THEY ARE RESTRICTED TO FIXED VALUES FOR A GIVEN ATOM. EACH ELEMENT HAS ITS OWN UNIQUE SPECTRUM THAT CAN ACT AS A FINGERPRINT FOR THAT ELEMENT.

THERMAL ENERGY – ELECTRIC CURRENT THROUGH A FILAMENT OR FROM A FLAME CHEMICAL ENERGY FROM CHEMICAL BONDS BEING BROKEN AND FORMED – CHEMILUMINESCENCE FLUORESCENCE – ABSORPTION OF SHORT WAVELENGTH LIGHT (UV) AND EMISSION OF LONGER WAVELENGTH (VISIBLE) LIGHT PHOSPHORESCENCE – SAME AS FLUORESCENCE, BUT WITH A TIME DELAY

SPECTRUM – PLOT OF LIGHT INTENSITY VERSUS WAVELENGTH OR FREQUENCY (PLURAL IS SPECTRA). ABSORPTION SPECTRUM – PLOT OF LIGHT ABSORBED VERSUS WAVELENGTH OR FREQUENCY. EMISSION SPECTRUM – PLOT OF LIGHT EMITTED VERSUS WAVELENGTH OR FREQUENCY.

WHEN HEATED, SOLIDS EMIT CONTINUOUS OR BAND SPECTRA (LIGHT DISTRIBUTED OVER A RANGE OF WAVELENGTHS). THE MAXIMUM OR PEAK WAVELENGTH OF THIS BAND DEPENDS ON ABSOLUTE TEMPERATURE. max = b/T IN OTHER WORDS, AS THE TEMPERATURE INCREASES, THE PEAK SHIFTS TO SHORTER WAVELENGTHS (HIGHER ENERGY).

ATOMS IN A GAS EMIT LINE SPECTRA WHEN HEATED. LINE SPECTRA – LIGHT AT SPECIFIC WAVELENGTHS. THIS IS BECAUSE THE ELECTRONS CAN ONLY OCCUPY SPECIFIC ENERGY LEVELS.