2Comparison Of Chemical and Nuclear ReactionsNuclear Reactions1Elements may beconverted from one toanother.2Particles within thenucleus, such as protonsand neutrons, areinvolved in reactions.Chemical Reactions1No new elements can beproduced, only newchemical compounds.2Usually only the outermost electrons participatein reactions.
3Comparison Of Chemical and Nuclear ReactionsNuclear Reactions3Release or absorbimmense amounts ofenergy, typically 1000times more.4Rates of reaction arenot influenced byexternal factors.Chemical Reactions3Release or absorb muchsmaller amounts ofenergy.4Rates of reaction dependon factors such asconcentration, pressure,temperature, andcatalysts.
4The NucleusRemember that the nucleus is comprised ofthe twonucleons: protons and neutrons.The number of protons is the atomic number.The number of protons and neutrons togetheris effectively the mass of the atom.
5The NucleusTerminology used in nuclear chemistry.1.Nucliderefers to a nucleus with specificnumbers of protons and neutrons.2.Isotopesare nuclei that have the samenumber of protons but different neutronnumbers.Isotopes are the same element.
6RadioactivityNuclides of many elements are unstable.They decay spontaneously, emittingsubatomic particles and electromagneticradiation.We refer to these nuclides asradioactive.
7Neutron-Proton RatiosAny element with more than one proton(i.e., anything but hydrogen) will haverepulsions between the protons in thenucleus.Astrong nuclear force(Nuclear bindingenergy) helps keep the nucleus from flyingapart.
8Neutron-Proton RatiosNeutrons play a key role stabilizing thenucleus.Because they help attract other nucleons throughstrong nuclear force.They lack the repulsive forces associated with thepositive charges of protons.Therefore, the ratio of neutrons to protons is animportant factor in determining nuclear stability.
Tro, Chemistry: A Molecular Approach9Valley of Stability (Belt of Stability)for Z = 1⇒20,stable N/Z ≈ 1for Z = 20⇒40,stable N/Z approaches 1.25for Z = 40⇒80,stable N/Z approaches 1.5for Z > 83,there are no stable nuclei
10Stable NucleiNuclei above this belt (orband, valley ) have toomany neutrons.Some neutrons need to beconverted to protons forthe nuclei to be stable.
11Stable NucleiNuclei below the belt havetoo many protons.Some protons need to beconverted to neutrons forthe nuclei to be stable.
12Stable NucleiThere are no stable nuclei with an atomicnumber greater than 83, regardless of theirneutron to proton ratio.These nuclei tend to decay into smallernuclei.
13Experimentally, it can be shown thatnuclei have a preference for evennumbers of protons and neutrons.