Atoms, Molecules, and Ions
The Theme of Nuclear Chemistry in Atoms, Molecules, and Ions
The Atom Bomb
From what we know about atoms, they aren't really bomb-shaped (or sized). They do not explode and they are the building blocks of all things chemistry. So what's the deal with an atomic bomb? Are they mini carbon atoms that explode on impact? Nope. Let's clear up all the confusion.
Way back in the 1930's, there was an Italian physicist by the name of Enrico Fermi who wanted to try and make a new element. What can we say, some people like to try out new cookie recipes while others like to make new elements. Fermi's approach was to take the heaviest known element (at that time) and hit it with a stream of neutrons. The thought was that if an additional neutron were incorporated into the nucleus of a uranium atom, the nucleus might undergo a beta decay.
Without going into too much detail, beta decay is the process of converting a neutron into a proton. This process releases an electron. If Fermi's idea worked, a new element with atomic number 93 would be synthesized for the first time. We have a feeling this element would be called Fermitunium rather than Neptunium if this had worked.
Enrico Fermi: Suit model and scienctist (1901-1954). (Image from here.)
Fermi's Idea in Equation Form:
As any good scientist would do, Fermi promptly performed his experiment. He did detect the emission of beta particles, which is the fast moving electron released during beta decay, but his results ended up being inconclusive. Had he synthesized a new element? It's unclear. He never chemically examined the products to determine their composition and therefore could not say with certainty whether he had or had not. There must have been a really important football game on that weekend.
A few years later three researchers in Germany, Lise Meitner, Fritz Strasmann, and Otto Hahn decided Fermi's experiment was worth repeating and analyzing more carefully. What they found would change the world forever, and we're definitely not being dramatic. This was mind-blowing world-altering stuff we're talking about.
After analysis of the products, they found several elements lighter than uranium, not heavier as Fermi predicted. On January 6, 1939, they reported that the neutron bombardment of uranium resulted in nuclear fission, which is the splitting of the atom. All this time scientists thought atoms were completely and totally indivisible, but that wasn't the case. Slamming uranium with a neutron stream had broken apart the uranium atoms into barium, krypton, and other smaller products. Another very important component of this reaction was the incredible amount of energy that was released.
Meitner, Strasmann, and Hahn's Findings in Equation Form:
One interesting thing to note is that the isotope of the initial uranium used, U-235, is not the most abundant form of uranium on the planet. As a matter of fact, U-235 makes up less than 1% of all naturally occurring uranium. The most abundant form, U-238, does not undergo fission. Crazy, huh? Therefore, the uranium used for fuel in nuclear reactions must be enriched in U-235, meaning it must contain more U-235 than is naturally occurring.
You've probably heard the term "uranium enrichment" on the news or maybe even in your classrooms.2,3 Uranium enrichment is a heavily (and globally) regulated process that increases the percentage of U-235 in samples of uranium. There are many techniques but the most common involves a giant gas centrifuge that spins samples of uranium very quickly and helps separate U-235 from other naturally occurring isotopes of uranium.
Gas Centrifuge for U-235 Enrichment. (Image from here.)
Once uranium is enriched with U-235, it can undergo a chain reaction in which neutrons produced by the fission of one uranium nucleus can induce fission in other uranium nuclei. The process continues until the whole sample of U-235 is gone. What is left is a whole bunch of lighter elements and a whole bunch of energy.
Fission Chain Reaction
The amount of energy produced is enormous. It is enormous enough to generate a deadly and catastrophic bomb, or what we know as the atomic bomb. While it is not easy to produce enough enriched U-235 to make an atomic bomb capable of mass destruction, we all know it's possible.
In 1941, in the midst of World War II, the US government began a top-secret endeavor called the Manhattan Project. Its main goal was to enrich enough U-235 and build an atomic bomb before the Germans did. The project was led by physicist J. R. Oppenheimer and was headquartered in Los Alamos, New Mexico. After four years of research, the world's first nuclear weapon was successfully detonated at a test site in New Mexico. This first bomb exploded with a force equivalent to 18,000 tons of dynamite.4
The US did not need to use their new atomic bomb building skills on Germany. They had already been defeated by the time the bomb was constructed. Instead, the atomic bomb was used on Japan during World War II. One bomb was dropped on the city of Hiroshima and a second bomb was dropped on the city of Nagasaki. Together, the two bombs killed approximated 200,000 people and forced Japan to surrender. World War II was over, but the atomic age had begun.
The power behind the atomic bomb (nuclear fission) has also been used for good, including the generation of enormous amounts of "clean" energy/electricity through nuclear reactors. However, it is always important to remember that with great power comes great responsibility.