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How are atoms formed? – Joshua, 7, Shoreview, Minnesota
Richard Feynman, the famous theoretical physicist who won the Nobel Prize, said that if he could transmit only one piece of scientific information to future generations, it would be that everything is made of atoms.
Understanding how atoms are formed is a fundamental and important question because they make up everything from mass.
The question of where atoms come from takes a lot of physics to fully answer – and even then physicists like me only have good guesses to explain how some atoms form.
What is an atom?
An atom consists of a heavy center called the nucleus, which is made up of particles called protons and neutrons. An atom has lighter particles called electrons, which you can imagine orbiting the nucleus.
Each electron has one unit of negative charge, each proton has one unit of positive charge, and neutrons have no charge. An atom has the same number of protons as electrons, so it is neutral – it has no overall charge.
Now, most atoms in the universe are of the two simplest kinds: hydrogen, which has one proton, zero neutrons, and one electron; and helium, which has two protons, two neutrons, and two electrons. Of course, there are many atoms on Earth that are as common as carbon and oxygen, but I’ll talk about those in a moment.
An element is what scientists call a group of atoms that are all the same because they all have the same number of protons.
When were the first atoms formed?
Most of the hydrogen and helium atoms in the universe formed about 400,000 years after the Big Bang, which scientists believe gave birth to the universe, about 14 billion years ago.
Why did they form at that time? Astronomers know from observing distant exploding stars that the universe has been expanding since the Big Bang. When hydrogen and helium atoms first formed, the universe was about 1,000 times smaller than it is today.
And based on their understanding of physics, scientists think the universe was much hotter when it was smaller.
Before that, electrons had too much energy to settle into orbits around the hydrogen and helium nuclei. Thus, hydrogen and helium atoms could only form when the universe cooled to about 5,000 degrees Fahrenheit (2,760 degrees Celsius). For historical reasons, this process is mistakenly called recombination—combination would be more descriptive.
The nuclei of helium and deuterium, a heavier form of hydrogen, formed even earlier, just minutes after the Big Bang, at temperatures above 1 billion F (556 million C). Protons and neutrons can collide and form such nuclei only at very high temperatures.
Scientists believe that almost all ordinary matter in the universe consists of about 90% hydrogen atoms and 8% helium atoms.
How are more massive atoms formed?
Thus, hydrogen and helium atoms formed during recombination, when cooler temperatures allowed electrons to drop into orbits. But you, me, and almost everything on Earth is made up of much more massive atoms than just hydrogen and helium. How were these atoms created?
The surprising answer is that stars form more massive atoms. Creating atoms with multiple protons and neutrons bound together in a nucleus requires these types of high-energy collisions that occur in very hot places. The energy required to form a heavier nucleus must be large enough to overcome the repulsive electrical force that positive charges, like two protons, feel on each other.
Protons and neutrons also have another property, similar to a different type of charge, that is strong enough to bind them together once they are able to come together. This property is called the strong force, and the process that brings these particles together is called fusion.
Scientists believe that most elements from carbon to iron are fused in stars heavier than our Sun, where temperatures can exceed 1 billion F (556 million C), the same temperature as the universe when it was just a few minutes old.
However, even hot stars will not form elements heavier than iron and nickel. This requires additional energy because heavier elements can break into pieces more easily.
In a dramatic event called a supernova, the inner core of a heavy star suddenly collapses after it runs out of fuel. In a powerful explosion, this collapse causes elements heavier than iron to form and be ejected into the universe.
Astronomers are still working out the details of other fantastic stellar events that form larger atoms. For example, colliding neutron stars can release enormous amounts of energy – and elements such as gold – to form black holes.
Understanding how atoms are formed requires learning a bit of general relativity as well as some nuclear, particle and atomic physics. But to complicate things, there is other stuff in the universe that doesn’t seem to be made of ordinary atoms, called dark matter. Scientists are investigating what dark matter is and how it can form.
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This article is republished from The Conversation, a not-for-profit independent news organization that provides facts and sound analysis to help make sense of our complex world. Written by: Stephen L. Levy, Binghamton University, State University of New York
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Stephen L. Levy receives funding from the National Science Foundation and the National Institutes of Health. He is affiliated with CyteQuest, Inc.