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Unformatted text preview: ly charged protons, but
we know that like charges repel each other… so why doesn’t the
nucleus fall apart?
• Nucleus held together by the “STRONG FORCE”
Puzzle #1: what could possibly lower the mass of 12C so that it is
• Strong force means there is a binding energy holding the
nucleus together – separating the protons and neutrons would
require a defined energy input
• Energy is equivalent to mass: E = mc2
• So total mass left after separating the n, p, and e from 12C also
must account for the energy required to split these! Isotopes
A nucleus has a definite number of protons (Z), a definite
number of neutrons (N) with atomic number A = Z + N
Elements have a defined number of protons (Z)
Isotopes of an element have same Z, differing numbers of
neutrons (so different N and thus also A)
For example, take the element carbon:
the most common isotope of carbon has 6 protons and 6
neutrons (denoted 12C; 98.9% abundance)
Z = 6; N = 6; A = 12
another stable isotope of carbon has 6 protons and 7
neutrons (denoted 13C; 1.1% abundance)
Z = 6; N = 7; A = 13
an unstable isotope of carbon has 6 protons and 8 neutrons
(denoted 14C; half-life is 5730 years) More examples of isotopes Fission of uranium • Barium and krypton r...
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This document was uploaded on 12/05/2013.
- Fall '13