Atomic Structure Slide 1 of 18

Go to slide: 1: Atomic Structure 2: Isotopes 3: Nuclear Forces 4: Radioactive Decay 5: Electromagnetic Spectrum 6: Ionizing radiation 7: Alpha radiation characteristics 8: Beta radiation characteristics 9: Gamma & X-ray 10: Neutron radiation characteristics 11: Charged Particle Interactions 12: Photon Interactions 13: Neutron Interactions 14: Neutron Interactions 15: Neutron Interactions 16: Detecting Radiation 17: Radiation Detection 18: Measuring Radioactivity

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Everything in the world is made up of extremely small particles called "atoms." An atom consists of a very dense nucleus with small particles orbiting around it. This atom is a normal atom of helium. The nucleus consists of two positively charged PROTONS and two neutrally charged particles called NEUTRONS. The mass of a proton is less than one billionth of a gram. To make it more convient to work with, a relative mass scale was developed where an "atomic mass unit" is equal to the mass of a proton. The neutron also weighs 1 amu. The electron weighs 1800 times less than the proton. It carries a minus one charge. Chemical properties are determined primarily by the outer shell electrons. The number of electrons will equal the number of protons in a normal atom. Atoms are identified by the number of protons in the nucleus. This is called the atomic number or "Z" number. This also identifies which element the atom is. The total number of particles in the nucleus also helps to identify the atom. We call this number the atomic mass number or "A" number. Both of these numbers are used together to identify atoms.