42_nucleus - Lesson 42: Inside the Nucleus Nuclear physics...

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Lesson 42: Inside the Nucleus Nuclear physics gets its name from the fact that we are concerned with only the nucleus of the atom. Chemistry needs to pay attention to the electrons of the atom, since electrons determine how the chemical bonds form. Nuclear physics is concerned with the nucleus, since the nucleus determines the element as well as the nuclear reactions that can happen. The Nucleons Nucleon is the name given to anything that you find in the nucleus . This includes protons and neutrons. Protons symbol is p + positive charge = +e mass = m p = 1.6726e-27 kg number of protons in a nucleus = atomic number → symbol is Z It is the number of protons in the nucleus that determine which element you are dealing with. A single proton is the entire nucleus of the simplest atom, hydrogen Neutrons symbol is n 0 no charge mass = m n = 1.6749e-27 kg number of neutrons in a nucleus = neutron number symbol is N The total number of nucleons ( protons + neutrons ) in a nucleus is called the atomic mass number → symbol is A . A = Z + N A = atomic mass number = # of nucleons Z = atomic number = # of protons N = neutron number = # of neutrons Writing out Symbols To write down which nucleus we have, we use the chemical symbol from the periodic table along with the A and Z values. The A and Z values are always written to the left of symbol, with A on top. X Z A 11/28/2008 © studyphysics.ca Page 1 of 5 / Section 16.1 Remember “e” stands for “elementary charge”, and does not necessarily have anything to do with electrons. Notice that a neutron does have a slightly bigger mass than a proton. This will be important later.
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Example 1 : An nucleus has 7 protons and 8 neutrons. Identify what element it is, and write out its symbol. According to the periodic table, the element with 7 protons is nitrogen. Since nitrogen has 7 protons , its Z value is 7 . To get the A value, we have to add the number of protons and neutrons to get 15 . N 7 15 Since we can just look up the atomic number of an element on the periodic table, we often skip writing the value for Z so… N 15 We read this as nitrogen-fifteen or N-15 . Example 2 : If a nucleus has the symbol Na 11 23 then identify as much as you can about it. From the periodic table we can see that this is the symbol for sodium . We can also see this from the atomic number being 11, which is the atomic number for sodium. Specifically, we would call it sodium-23 . This also means that the nucleus has
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This note was uploaded on 12/02/2011 for the course PHYSICS 235 taught by Professor Staff during the Fall '08 term at Rutgers.

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42_nucleus - Lesson 42: Inside the Nucleus Nuclear physics...

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