Nuclear Chemistry
Nuclear Forces The positive protons repel each other through electrostatic repulsion. the neutrons provides a ‘nuclear force’, or strong force This holds the nucleus together and stabilizes it. Neutron nucleons Proton
Nuclear Forces The nuclear force is only strong when the protons and neutrons are close together. The more protons = greater electrostatic repulsion This causes the nuclear force to weaken. So, even more neutrons are needed to stabilize the nucleus.
A neutron-proton ratio of 1.5 : 1 is at the limit of stability. Nuclear Forces A stable neutron - proton ratio is 1:1. A neutron-proton ratio of 1.5 : 1 is at the limit of stability.
Nuclear Forces Atoms with more than 83 protons cannot reach stability. All elements beyond bismuth on the periodic table are unstable and undergo some sort of ‘decay’ in order to become stable.
Nuclear Symbols Mass number (p+ + no) Element symbol Atomic number (number of p+)
Radioactive Decay Unstable nuclei will result in decay. This results in a change in the nucleus. Transmutation: a change in the identity of an element as a result of a change in the number of protons.
Radioactive Decay Atoms will decay by ejecting protons, neutrons, or altering them into different particles by releasing one or more of the following: Alpha rays Beta rays Gamma rays Positron Emission Electron Capture
Types of Radioactive Decay Alpha-particle Production Limited to VERY large nuclei.
Alpha Particles Alpha particles consist of two protons and two neutrons Helium Nucleus 2+ charge In alpha decay the atomic number will be reduced by two, and the mass number reduced by four.
Alpha Particles Alpha rays are relatively slow and easy to stop. A piece of paper will stop alpha particles. They will travel only a few centimeters before stopping The positive charge of the alpha particle attracts electrons The particle becomes a harmless helium atom.
Beta Particles A Beta particle is an electron created and emitted when a neutron is transformed into a proton and an electron during radioactive decay. This action adds a proton and thus changes the identity of the atom. The mass number stays the same.
Beta Particles Beta rays are generally stopped by thin sheets of metal such as aluminum. Their negative charge causes them to interact with other atoms which slows their speed. -
Gamma Rays Gamma rays are photons of electromagnetic radiation with high frequency and energy. Gamma rays are given off during some types decay. Gamma rays have no mass – they are pure energy.
Gamma Rays Gamma rays are incompletely blocked by thick concrete or lead
Gamma Rays Do not affect the identity of the atom since they have no mass and no charge. Gamma radiation may be released along with alpha or beta decay. Beta Particle Gamma Ray
Positron Emission A positron is a particle that has the same mass as an electron, but has a positive charge. A positron is emitted from the nucleus as a proton is converted into a neutron. The atomic number decreases by one but the mass number stays the same.
Electron Capture The nucleus can ‘capture’ one of its own inner-orbital electrons if the atom is unstable due to too many protons. The electron will combine with a proton in the nucleus and form a neutron. The atomic number decreases by one but the mass number stays the same.
Types of Radiation
Alpha particles are easy to stop, gamma rays are hard to stop.
Nuclear Fission The process of splitting an atom. http://www.teachersdomain.org/asset/phy03_vid_fission/ The process of splitting an atom. Releases an enormous amount of energy. 1 mol of uranium-238 can produce about 26 million times as much energy as 1 mol of methane.
Nuclear Fusion The process of combining two light nuclei. Produces more energy than fission. http://www.teachersdomain.org/asset/phy03_vid_fusiontest/
Nuclear Equation Both the atomic number and the mass number must be conserved. That is the sums of both on each side must be equal.
Decay Series Often radioactive nucleus cannot achieve stable state through a single decay process. A decay series will occur until a stable nuclide is formed.