I.ELECTRONIC STRUCTURE OF ATOMS
-arrangement of atoms’ electrons
-the number of electrons in an atom
-distribution of electrons around the nucleus and their energies
*Billiard Ball Model (JOHN DALTON)
*Plum Pudding Model (JOSEPH J. THOMPSON)
*RUTHERFORD’s Model of Atom
-atoms are tiny, hard, indivisible spheres
-electrons (negative charge) occupy the atom
- Atom is mostly empty space with a dense nucleus
•PROBLEMS with Rutherford’s Model
*According to laws of physics, Rutherford’s atom should collapse *The model CANNOT explain differences in properties of elements *The model CANNOT explain the colors emitted by elements when heated
A.THE QUANTUM MODELS (WAVE)
-formed through studies about light
•DESCRIBING ELECTROMAGNETIC WAVE
-distance between two adjacent peaks or troughs (m)
*Frequency (ѵ ”nu”)
- number of cycles(complete wavelengths) that pass a given point each second (Hz or /s)
**Wavelength is inversely proportional to frequency.
↔ c= 3.00 x 10⁸m/s B.QUANTIZED ENERGY AND PHOTONS
oPerfect absorber and emitter of light
oAt high temperature, solids emit radiation
oRadiation depends on the temperature not in the element the solid is made from. oPREDICTION: “As temperature increases, the frequency of light emitted also increases.” oOBSERVATION: There was a peak.
•Photoelectric Effect and Photons
oWhen a beam of light shines on a certain surface (e.g. some metals), electrons are ejected. oThe effect is instantaneous.
oPREDICTION: ”It will take time for effect to be observed”; “and light will produce the effect, given enough time” oOBSERVATION: Effect is instantaneous. There is a minimum frequency of light needed to produce the effect. o**”If frequency of light is below a certain value called the threshold frequency, the number of electrons will be ejected.” o**”If intensity of light is increased, flow of current also increases.”
•QUANTUM THEORY (Max Planck *1858-1947*)
oQuantum (fixed amount) – smallest quality
oEach particle corresponds to certain energy.
oPlanck proposed that the minimum amount of radiant energy that can gain or lose is related to the frequency of radiation. o”Radiation consists of packets/quantum of energy (PHOTONS *name given by G.N. Lewis*).” oQuantum Theory: “Energy is quantized. It can only have certain allowed values.” oEnergy of radiation is proportional to the frequency of radiation. Higher frequency More energy; Lower wavelength More energy oMonochromatic light consists of photons with the same frequency or same energy. oIntensity of the light depends on the number of photons emitted per second. •Einstein’s Explanation on the Photoelectric Effect
oLight consisting of energy packets hit the metal and their energy is absorbed by the electrons. oOne packet of energy (photon) hits the metal surface, one electron is emitted. oIf energy of a bundle is not enough, it will not be able to dislodge electron from the attraction of the atomic nuclei. No photoelectric effect. oIf energy of a bundle is enough (equal to the threshold energy). It will dislodge an electron from the attraction of the atomic nuclei. oEnergy in excess of energy to dislodge electron (in excess of the threshold energy) becomes kinetic energy of the electron. oHigher energy/ frequency of light more excess energy Higher kinetic energy of electron C.LINE SPECTRA AND THE BOHR MODEL
oMonochromatic radiation is composed of single wavelength.
oSpectrum is produced when radiation from light is separated into different wavelength components. oContinuous spectrum
ROYGBIV, containing light of all wavelength
Spectrum containing radiation of only...