Ch 9 - Atomic and Nuclear

Question 1

photoelectric effect

Answer 1

• high frequency light is shot onto metal in vacuum - metal atoms emit electrons
• electrons produce a current
  
  • current - net charge flow per time
• threshold frequency - minimum frequency of light that causes ejection of electrons
  
  • dependent on metal

Question 2

Photons

Answer 2

• light beam consists of integral number of light quanta (photons)
• energy of photon is proportional to frequency of light
• E = hf
  
  • h is planks constant (6.6E-34 J*s)

Question 3

Energy of ejected electron

Answer 3

• K_max = hf -W
• W = hf_T
  
  • f_T = threshold frequency

Question 4

Atomic absorption and Emission

Answer 4

• Absorption - electron jumps from lower to higher energy orbit by absorbing a photon of the exact energy difference
• Emission - electron falls from hert to lower energy level and emits a photon of equal energy difference
• can be compared to IR spectroscopy and UV-Vis
• used to produce color in pH indicators (aromatic rings and conjugated double bonds)

Question 5

Fluorescence

Answer 5

• due to multi-step emission of photons
• ultraviolet radiation used to excite the material

Question 6

Mass Defect

Answer 6

• due to matter converted to energy
• E = mc²
• a small mass will produce a large amount of energy due to the squared speed of light

Question 7

Nucleus

Answer 7

• nucleons - protons and neutrons
• strong nuclear force - compensates for electromagnetic repulsion of protons in the nucleus
  
  • bonded energy is lower than the constituents
  • difference is radiated away via heat, light, radiation
• binding energy - energy radiated away from nucleus
  
  • higher binding energy - more stable nucleus
    
    • iron is most stable
• weak nuclear force, electrostatic forces, and gravity are the other fundamental forces of nature

Question 8

Isotopic notation

Answer 8

• atomic number (Z) as subscript
• mass number (A) as superscript
  
  • = protons + neutrons

Question 9

Fusion

Answer 9

• small nuclei combine to form a larger nucleus
• hydrogen fusion occurs in the sun
  
  • mass deficit produces energy

Question 10

Fission

Answer 10

• large nucleus splits into smaller nuclei
• induced fission reactions release neutrons that go on to cause more reactions
  
  • nuclear power plants

Question 11

Radioactive decay

Answer 11

• decay of nuclei and emission of particles
  
  • balanced equations:
    
    • equal atomic numbers
    • equal atomic masses
• Alpha - emission of alpha particle (helium nucleus)
  
  • 2 protons, 2 neutrons, no electrons
  • +2 charge particle
• Beta - emission of beta particle (electron)
  
  • can be positive or negative charge
  • electron or positron
  • B- decay is conversion of neutron into an electron and proton
    
    • mass number is constant, Z’ is Z+1
  • B+ decay is conversion of proton into a neutron and positron
    
    • mass number is constant, Z’ is Z-1
• Gamma - emission of gamma rays (high energy photons)
  
  • no charge
  • lower energy of parent nucleaus
  • no change in mass

Question 12

Electron Capture

Answer 12

• reverse B- decay
• inner electron combines with a proton to form a neutron
• atomic mass is constant
• atomic number decreases by 1

Question 13

Half life

Answer 13

• time for half of the sample to decay

Question 14

Exponential Decay

Answer 14

• number of radioactive nuclei that have not decayed
• rate of decay is proportional to the number of nuclei that remain
• n = n₀e^-(lambda*t)
  
  • lambda - decay constant