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How do atoms form? – Joshua, age 7, Shoreview, Minnesota
Richard Feynman, a famous theoretical physicist who won the Nobel Prize, said that if he could pass on only one piece of scientific information to future generations, it would be that all things are made of atoms.
Understanding how atoms form is a fundamental and important question, since they make up everything with mass.
The question of where atoms comes from requires a lot of physics to be answered completely – and even then, physicists like me only have good guesses to explain how some atoms are formed.
What is an atom?
An atom consists of a heavy center, called the nucleus, made of particles called protons and neutrons. An atom has lighter particles called electrons that you can think of as orbiting around the nucleus.
The electrons each carry one unit of negative charge, the protons each carry one unit of positive charge, and the neutrons have no charge. An atom has the same number of protons as electrons, so it is neutral − it has no overall charge.
An atom consists of positively charged protons, neutrally charged neutrons and negatively charged electrons.
AG Caesar/Wikimedia Commons, CC BY-SA
Now, most of the atoms in the universe are 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, on Earth there are lots of atoms besides these that are just as common, such as carbon and oxygen, but I’ll talk about those soon.
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 did the first atoms form?
Most of the universe’s hydrogen and helium atoms formed around 400,000 years after the Big Bang, which is the name for when scientists think the universe began, about 14 billion years ago.
Why did they form at that time? Astronomers know from observing distant exploding stars that the size of the universe has been getting bigger since the Big Bang. When the hydrogen and helium atoms first formed, the universe was about 1,000 times smaller than it is now.
And based on their understanding of physics, scientists believe that the universe was much hotter when it was smaller.
Before this time, the electrons had too much energy to settle into orbits around the hydrogen and helium nuclei. So, the hydrogen and helium atoms could form only once the universe cooled down to something like 5,000 degrees Fahrenheit (2,760 degrees Celsius). For historical reasons, this process is misleadingly called recombination − combination would be more descriptive.
The helium and deuterium − a heavier form of hydrogen − nuclei formed even earlier, just a few…
