chem concepts

Question 1

black body effect

Answer 1

• a substance that absorbs & emits all wavelengths of light
• temperature-dependent photo-emission: higher temperature = shorter wavelength & lower temperature = longer wavelength
• classical physics said: any piece of matter that makes up the black body can vibrate at any frequency & assume any energy; energy & matter = continuous
• quantum physics says: vibrating electrons can vibrate & emit energy only at discrete frequencies (energy of light is quantized by its frequency)
• Planck: energy comes in clumps called “quanta”
  E = nhv

Question 2

photoelectric effect

Answer 2

• provided support for the particle nature of light
• classical physics said:
• increasing amplitude = increased kinetic energy of emitted photoelectrons
• increasing frequency = increased current (rate of electrons being ejected)
• when light is dim, there should be a lag time
• energy scales (is proportional) with square of amplitude
• what really happened:
  increasing amplitude = increased current
  increasing frequency = increased kinetic energy of emitted photo-electrons
  *energy scales linearly with frequency of light for 1 ‘photon’ (light packet) AND energy comes in discrete packets & scaled with number (n) of packets
  Etotal = nEphoton = nhv

we discovered: there is a threshold frequency-minimum frequency of electromagnetic radiation required for the phenomenon of photoelectric emission to occur from a metal surface

• einstein: proposed that light behaved like a stream of particles called “photons”
  E = hv
  E = hc/ƛ

light is behaving somewhat particle-like

Question 3

heisenberg uncertainty position

Answer 3

• the more i know the wavelength, the more i understand it’s momentum, but the less i know about it’s position
• bohr model is in complete contradiction bc it says that the radius of the orbit is quantitatively known & velocity