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The atom is thought of as electrons in a cloud moving around a compact nucleus.
- The nucleus is made of protons and neutrons, also known as nucleons.
- The nucleus is held together by extremely short-ranged forces called the “strong force” and the “weak force”
- Conventional symbols are used to quickly communicate the make-up of a nucleus.
- The nucleus is made of two types of particles. Atoms may have up to about 100 protons and about 150 neutrons!
- Protons are positively charged particles that have a mass of about 1 atomic mass unit (amu).
- Neutrons are particles with NO charge and a mass of about 1 atomic mass unit (amu).
- Isotope (ī´sƏ-tōp´) – One of two or more atoms having the same atomic number but different mass numbers.
- The strong nuclear force holds nuclear particles together.
- The strong nuclear force keeps protons and neutrons from breaking apart into yet smaller particles.
- The strong nuclear force acts over a very small distance (10-15 m).
- The weak nuclear force is the force that acts to hold nucleus together.
- The weak nuclear force acts over a very small distance (distances no larger than a nucleus).
How to Use This Cheat Sheet: These are the keys related this topic. Try to read through it carefully twice then recite it out on a blank sheet of paper. Review it again before the exams.
- The weak nuclear force is weaker than the “strong nuclear force” – only 10-13 times as strong! Sometimes is overcome by other forces causing the atom to cleave or give off radiation.
- Binding energy can be calculated using E=mc2.
- Binding energy is the energy needed to hold the nucleus and its particles together.
- Binding energy comes from the actual mass of the particles in the nucleus!
- On this scale, it is convenient to use the electron-volt as a unit of energy.
- Conversion: 1 eV= 1.602 x 10-19 J
The Nucleus and Nuclear Physics
Calculating Binding Energy
Determine the masses of each of the 4 particles individually.
Determine the mass of a He nucleus.
The difference between the two provides “m”.
Use m in the equation E=mc2 to calculate E
Radioactive decay usually takes on one of three specific forms, known as alpha, beta and gamma decay.
It is useful to know the amount of time needed for half of a sample to decay – this is called the “half-life”.
Alpha decay results in the emission of a helium nucleus
Relatively large Relatively slow Relatively low energy
Stopped more easily than other decay particles
Beta decay results in a different nucleus of the same atomic mass but atomic number 1 greater.
Larger, faster and higher energy than alpha particle
Greater ability to penetrate than alpha particle
Gamma rays are usually highly energetic
No new element is formed; rather the remaining nucleus is less energetic
Move at the speed of light – high energy
Penetrate most matter
Half-Life – Amount of TIME taken for one half of the original nuclei to decay.
Nuclear power plants have provided energy for half a century. Atomic bombs are based on fission and among the most destructive weapons ever created. Medical applications of radioactivity are commonplace in our society, and are seen in cancer therapy, tracers, tomography (PET scans), NMRs and MRIs.