Nuclear Chemistry
Isotopes
Two main forces in nucleus
1. Strong nuclear force—all nuclear particles attract each other
Proton-proton
interaction is weak Neuton-neutron interaction is weak Neutron-neutron interaction 2 x as strong
When the protons and neutrons are in good balance, the nucleus is quite stable.
The other force is… 2.
Electomagnetic force Makes
protons repel each other
What determines stability? Balance between strong force and electric force Neutron:proton ratio in nucleus
– Most stable between 1:1 and 1.5:1
Atoms want to be stable and will decay to attain it.
Binding Energy When atoms decay they release a lot of energy because they are achieving a more stable state. How much? It depends on the binding energy. Binding energy
– Energy released when a nucleus is split into its nucleons – Formula for the Binding Energy is E = mc2
Think of an Oxygen Atom 8
p+ + 8 no = 16.13 amu
Oxygen
atom = 15.99 amu
Difference
is 0.14 amu E = 0.14amu x c2 x 1 mol = 1.23 x 1013 J =420,000 kg coal
Unstable Nuclei Most
atoms have stable nuclei. All elements with atomic number ≥84 are unstable. Unstable nuclei (i.e., “radioactive” nuclei) undergo spontaneous change, giving off energy or particles when they change.
Nuclear Reactions 2 basic types Transmutation – nucleus of one element is transformed into nucleus of different element Nuclear reactions affect the nucleus of an atom
9 4
Be 24He 126C 01n
Nuclear Reactions – Fission: a very heavy nucleus splits into two smaller nuclei
– Fusion: two nuclei with small masses combine to form heaver, more stable nuclei
Elements
heavier than Fe-56 tend toward fission to become more stable.
Elements
lighter than Fe-56 use fusion to become more stable.
Particles in Nuclear Decay
3 main types – Alpha particles 2 protons, 2 neutrons—a helium nucleus +2 nuclear charge
4 2
4 2
He
– Cannot penetrate skin; dangerous if ingested – Can be stopped by a piece of paper
Nuclear Particles, cont.
Beta particles An electron emitted from the nucleus 0 -1 charge, tiny mass (neutron into -1 proton) Fast moving, can penetrate into skin Can be stopped by aluminium or glass Gamma particles High energy electromagnetic waves 0 emitted from nucleus 0 No mass, no charge Very penetrating; may not be stopped by several feet of concrete
More Nuclear Particles
Positrons
Neutrons – 1 amu, no charge
0 – Mass of electron, positive charge 1 – Proton into neutron with a positron emitted
Protons
1 0
1 1
n
– 1 amu, +1 charge p – Particle Video – Fusion/Fission summary
