Nuclear Chemistry The nucleus is a tiny part of each atom. How can it be the root of so much energy release?



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Nuclear Chemistry

  • The nucleus is a tiny part of each atom. How can it be the root of so much energy release?


Nuclear Chemistry

  • To understand where all that energy comes from, one must first know what constitutes the nucleus of an atom.

  • The nucleus is the domain of protons and neutrons.

  • Protons have a positive charge and are usually balanced by electrons, which are found outside the nucleus.

  • Neutrons have no charge.



Nuclear Chemistry

  • The number of protons in any atom’s nucleus is the atomic number of that element.

  • Oxygen atoms always have 8 protons in the nucleus.

  • Gold atoms always have 79 protons in the nucleus.

  • How many protons would every atom of molybdenum have?

  • If I have an atom with 49 protons in the nucleus, then it is ________.

  • 42, Indium

  • The number of protons gives the identity of the element.



Nuclear Chemistry

  • This is a nucleus with 30 protons and 42 neutrons. What element is it?

  • It is zinc. Look at zinc on your periodic table. Its atomic number is 30.

  • Zinc’s mass is also listed. It is 70 amu.



Nuclear Chemistry

  • Protons + neutrons = atomic mass

  • 30 protons + 42 neutrons = 72.

  • The periodic table indicates that zinc’s mass is approximately 70 amu. Is this nucleus still zinc?

  • Yes!

  • It’s an isotope of zinc.



Nuclear Chemistry

  • Nuclei can have different numbers of neutrons without changing the identity of the element.

  • Atoms of an element with different numbers of neutrons are called isotopes.

  • When you look at the periodic table of elements for the mass of any element, you are finding the weighted average of the masses of the naturally occurring isotopes of that element.

  • The most common isotope of any element can be found by rounding the given mass number to the nearest whole number. Look at gallium. The most common isotope of gallium is Ga-70. Why?



Isotopes – Nuclear Chemistry

  • These are two common isotopes of carbon.

  • C-12 is stable, and C-14 is radioactive.

  • Radioactive isotopes have an unstable nucleus that will decay.

  • What do the two isotopes have in common?



Nuclear Chemistry

  • Example: Let’s look at osmium. It’s right in the middle of your periodic table of elements.

  • An atom of osmium has how many protons?

  • I hope you said 76.

  • Osmium’s atomic mass is listed as 190.2. That means that most osmiums probably have a mass of 190 amu, while a few have a mass of 191 amu. They average out to 190.2 amu.

  • If I have a regular (most common) osmium atom, its protons and neutrons must add up to 190. I know that there are 76 protons, so the rest must be neutrons.

  • Protons + neutrons = atomic mass

  • 76 + N = 190

  • How many neutrons are in a common osmium atom?



Nuclear Chemistry

  • A regular osmium atom has 114 neutrons and 76 protons, giving it a total mass of 190 amu. That isotope of osmium may be called Os-190.

  • Another isotope could be Os-194. That’s an osmium atom with an atomic mass of 194 amu. How many protons and neutrons would it have?



Nuclear Chemistry

  • You know that protons are attracted to electrons and vice-versa, because opposite charges attract electrostatically.

  • What holds the particles in the nucleus together?

  • Protons repel other protons.

  • Neutrons have no attraction for protons or for each other.



Nuclear Chemistry



Nuclear Chemistry

  • Strong nuclear force holds all nuclei together, but for some isotopes, the force is not enough.

  • These isotopes decay naturally.

  • Isotopes of any atom that can decay are called radioactive.

  • C-14 decays over time at a predictable rate. It’s so dependable that scientists use C-14 dating to determine the age of many found objects. As it decays, C-14 turns into C-12, a non-radioactive isotope of carbon.



Nuclear Chemistry

  • When we overcome the strong nuclear force, energy is released.

  • A nuclear reaction is a reaction in which the nucleus is changed and energy is released.

  • The only way to change the identity of an atom is by changing the number of protons which are in its nucleus. What kind of reaction could do that?

  • Only a nuclear reaction can change the contents of the nucleus.



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