Nuclear Chemistry-Random Sources

Ways to Characterize a Nucleus
Atomic Number (Z)
Mass Number (A)
Size
Shape
Binding Energy
Angular Momentum
Half-Life (if unstable)
What is
“Nuclear Binding Energy”?
The energy which holds a nucleus together.

or

The energy required to split a nucleus up into its constituents.

Define “Half-Life”
The time required for half of the population of a group of unstable nucelei to decay.

Rate of decay is related to the mean lifetime of a decaying nucleus.

Can vary from billions of years to a tiny fraction of a second.

Define “Isotope”
A nucleus with the same Z (number of protons) but a different A (different atomic mass, which means different number of neutrons).
Define Isobar
A nucleus with different Z but the same number of A (atomic mass).
Would the chemical properties of isotopes be more different or more similar?

More similar.

 

This is because: Chemistry is the study of the interactions between protons and electrons.

Thus with the same number of protons and electrons present, chemically speaking, isotopes will behave very similarly to each other.

What are the three isotopes of Hydrogen?
Hydrogen (No neutrons)
Deuterium (1 Neutron)
Tritium (2 Neutrons, unstable)
Is the mass of an atom more or less than the sum of the individual masses of it’s constituents?
Less.

Energy is given off when

How does binding energy relate to the number of protons and neutrons in a nucleus?
Binding energy generally continues to grow as more nucleons are added to the nucleus.

This is true until roughly about A= 60, at ~8 MeV per nucleon.

Past A=60 the binding energy starts to decrease slowly up to the most massive nuclei, which have energy around 7 MeV.

List Three Important Nuclear Models
Liquid Drop Model
The Shell Model
The Collective Model
Generally speaking, the conflict between what forces limits the ability of a nucleus to grow?
The balance between the electromagnetic force and the nuclear forces create a limit.
What is the general goal of nuclear physics?
To account for the properties of nuclei in terms of mathematical models of their structures and internal motion.
What is the ratio of the nucleus to the total diameter of an atom?
1/100000
Define a “Nuclide”.
A specific nucleus defined by the number of protons (the atomic number) and neutrons present.

More generally each have a specific nucleon number (atoms mass)

Practice Question: 

A nuclide that has 26 protons and 33 neutrons is used to study blood chemistry.

 Write its nuclide symbol in the form of ZAX

  What are two other ways to represent this nuclide?

Because this nuclide has 26 protons, its atomic number, Z, is 26, identifying the element as iron, Fe.

 

This nuclide of iron has 59 total nucleons (26 protons + 33 neutrons), so its nucleon number, A, is 59.

 

5926Fe

 59Fe

 iron-59

Which two forces act upon the nucleus and help produce it’s structure?
The electrostatic (electromagnetic) and strong force.

For lighter elements, having an even proton to neutron ratio is suffice to keep a stable nucleus. 

For heavier elements does this trend stay the same, that is, is an even number of protons to neutrons enough to keep the nucleus stable?

 

If not then how does it change? 

No.

For heavier elements, more neutrons than protons start to become necessary.

This is because with the higher number of protons, the electromagnetic repulsion between grows, and more neutrons per protons are needed in order to compensate (with the strong force). 

Do nuclei exist that have no neutrons and more than one proton?

No, the electrostatic repulsion between the protons makes any such arrangements impossible. 

The neutrons are needed to help stabilize a nucleus. 

How many naturally occuring stable nuclei are there?

264 

Known, naturally occuring, stable nuclei. 

Describe the “Band of Stability”

 

Band of Stability

-Is is an area on a graph of protons to neutrons in which stable nuclei are found.

-A nuclide found outside of this band will likely undergo one or more nuclear reactions (radioactive decay) to make it fall into this band of stability.

-The band stops at 83 protons, but scientists postulate that around 114 protons and 184 neutrons should be an “island of stability”.

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Isotopes occurring above and to the left of the band of stability tend to emit what, and why?
-Beta emitters.
-Because they want to lose a neutron and gain a proton.
Those lying below and to the right of the band of stability tend to emit what, and why?
-Positron emitters
-Because they want to lose a proton and gain a neutron.
Isotopes above element 83 tend to emit what type of particle?
-Alpha Particle
-Because they have too many nucleons.
Describe the “Odd-Even” Rule.
When the numbers of neutrons and protons in the nucleus are both even numbers, the isotopes tends to be far more stable than when they are both odd.
What is the source of the “Odd-Even” Rule?
Has to do with the spins of nucleons (both have spin).
-When two protons or neutrons have paired spins (opposite spins), their combined energy is less than when they are unpaired.
Briefly describe what the “Magic Number” rule states.
Isotopes with certain numbers of protons or neutrons tend to be more stable then the rest.
What are the magic numbers of protons?
2, 8, 20, 28, 50, 82, 114
What are the magic numbers of neutrons?
2, 8, 20, 28, 50, 82, 126, 184