L3 - Introduction To Isotopes, Radioactivity And Radiocative Decay
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What keeps the nucleus intact?
The neutron - binds to proton via the nuclear force
How was radioactivity first discovered?
• wrapped photographic plates in black paper • placed phosporescent salts and uranium salts • uranium salts caused blackening
What is the concept of half life?
All readioactive elements decay with the same mathematical exponential law
What are the 3 types of radiation?
• alpha • beta • gamma
What are the types of radiation stopped by?
• alpha: few cm of air • beta: aluminium sheet (1mm thick) • gamma: lead (several cm, m of concrete)
What are alpha particles?
Positively charged helium nuclei
What is the best source of alpha particles?
Alpha decay of heavy atoms
What is alpha decay?
The parent atomic nucleus decays into a different atomic nucleus Mass number - 4 Atomic number - 2
What is beta decay?
Neutron transforming into a proton, with the emission of an e- and a neutrino Mass number = Atomic number + 1
What is gamma decay?
Produced after alpha/beta decay, daugther nucleus formed is left in an excitied state, decays to lower state by emitting a gamma ray photon
What is the decay constant?
The probability that a given radioactive nuclei will decay per unit time
What is the radioactive decay law?
N(t) = N(0)e - λt
What is half life?
The time talen for half the radioactive nuclei in a given sample to undergo decay
What is the decay of unstable atomic nuclei?
• first order decay • differntiating • differential is rate of change • sub in • half life
What does 1Bq equal?
1 disintegration per second
What does 1.0 Ci equal?
3.7 x10^10 Bq
What are isotopes?
Atoms of the same element that have the same number of protons (atomic number) but different number of neutrons (atomic mass)
What happens to the properties of isotopes?
They have the same chemical properties but different physical properties
How do neutrons stabilise the nucleus?
• nuclear force binds the protons and the neutrons • presence of neutrons reduces electrostatic repulsion of the protons to each other
What can render a nuclide unstable?
Having too few or too many neutrons
What do unstable nuvlei attempt to do?
Reach lower energy states by nuclear decay
Why do different isotopes exhibit virtually identical chemical behaviours (reactivity)?
As the chemical behaviour is largely governed by the electronic structure
What is the kinetic isotopes effect?
An exception - bond energies are affected by the mass of the atoms that form the bond - heavier isotopes react slower than lighter isotopes of the same element
What happens to the potential kinetic isotope effect as the atoms become heavier?
Difference becomes much less, usually negligible