1026907-Nota-Padat-Fizik-F5-Radioactivity - 10.1 NUCLEUS OF...

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10.1 NUCLEUS OF AN ATOM Describe the composition of the nucleus of an atom in terms of protons and neutrons Matter is made up of very small particles called atoms Each atom has a very small and very dense core called nucleus. Most of the mass of atom is contained in the nucleus The electrons move in orbits around the nucleus. There are a lot of empty spaces within atom A nucleus consists of a number of protons and neutrons. Protons and neutrons also known as nucleons. A proton has a unit positive charge. A neutron is an uncharged particle of about the same mass as the proton. An atom is neutral because it contains an equal number of negatively charged electrons. So the net charge is zero. Define proton number (Z) Proton number, Z, is defined as the number of protons in a nucleus The number of electrons = the number of protons An element is identified by its proton number Define nucleon number (A) Nucleon number, A is defined as the total number of protons and neutrons in a nucleus. Number of neutrons, N = A - Z What is nuclide A nuclide is an atom of a particular structure. Each element has nucleus with a specific number of protons. Nuclide notation X A Z Proton p 1 1 Neutron n 1 0 Electron e 0 1 A X A = nucleon number Z Z = proton number X = chemical symbol of the element Example C 12 6 Proton number of carbon = 6, carbon nucleus has 6 protons. The nucleon number of carbon is 12. So the number of neutrons in carbon nucleus is 12 – 6 = 6 117
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Isotopes Example: H 1 1 hydrogen H 2 1 deuterium H 3 1 tritium Isotopes are atoms with the same proton number but different nucleon number. Isotopes of an element contain the same number of protons and the same number of electrons. So isotopes have the same chemical properties chemical reactions involve the electrons in an atom. However they have different physical properties because their mass is different. Some isotopes exist naturally. Isotopes can also be made artificially. 10.2 RADIOACTIVE DECAY State what radioactivity Is Radioactivity random process spontaneous process 3 different types of radiation Radioactivity is the spontaneous and random disintegration (decay) of an unstable nucleus accompanied by the emission of energetic particles or photons. The nuclei of some atoms are unstable. The nucleus of an unstable atom will decay to become more stable by emitting radiation in the form of a particle or electromagnetic radiation. Random process means there is no way to tell which nucleus will decay, and cannot predict when it is going to decay. A spontaneous process means the process is not triggered by any external factors such as temperature of pressure. Alpha
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This note was uploaded on 02/17/2011 for the course PHYCIS 101 taught by Professor Annonymous during the Spring '10 term at Sunway University College.

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1026907-Nota-Padat-Fizik-F5-Radioactivity - 10.1 NUCLEUS OF...

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