Atomic and Nuclear Phenomena Flashcards
What is the photoelectric effect?
when light of a sufficiently high frequency is incident on a metal in a vacuum, the metal atoms emit electrons
What is threshold frequency?
fT - the minimum frequency of light that causes ejection of electrons
What is the equation for energy of a photon?
E = hf E = energy of a photon of light h = Planck's constant (6.626x10-34 J) f = frequency of light
What is the equation for maximum kinetic energy of the ejected electron?
Kmax = hf - W W = work function
What is the work function?
the minimum energy required to eject an electron and is related to the threshold frequency of that metal
W = hfT
What is the relationship between energy, matter and speed of light?
E = mc^2
What is strong nuclear force?
the force that holds protons and neutrons together; compensates for the repulsive electromagnetic force between protons but only works over short distance
What is the weak nuclear force?
also contributes to stability of nucleus but one millionth as strong
What is the mass defect?
the difference between the theoretical mass of an element and the actual mass
What is the atomic number?
Z - corresponds to the number of protons in the nucleus
What is the mass number?
A - number of protons plus neutrons
What is fusion?
when small nuclei combine to form a larger nucleus
What is fission?
process by which large nucleus splits into smaller nuclei
What is radioactive decay?
naturally occurring spontaneous decay of certain nuclei accompanied by the emission of specific particles
What is alpha decay?
the emission of an alpha particle - will leave the daughter nucleus with an atomic number two less than the parent and the mass number is four less
What is an alpha particle?
42He nucleus - 2 protons, 2 neutrons and zero electrons
What is beta decay?
emission of a beta particle - results in same mass number but an atomic number one higher
What is a beta particle?
an electron
What is a positron?
has the mass of an electron but with a positive charge
What is gamma emission?
emission of gamma rays - no change in mass or atomic number, just emission of a gamma ray
What are gamma rays?
high energy (high-frequency) photons
What is electron capture?
when the element captures an electron so the atomic number becomes one less; opposite of beta decay
What is half life?
sample is the time it takes for half of the sample to decay
What is the equation for exponential decay?
n = n0*e^-lambda*t n0 = number of undecayed nuclei at time t = 0 lambda = decay constant n = radioactive nuclei that have not yet decayed in a sample
How is the decay constant related to half-life?
decay constant = 0.693/T(1/2)
