Helium-4

Helium is a very light gas.

It is found all over space. It is also on our Earth. Most helium comes from heavy bits in the ground.

In space, it is everywhere. It makes up much of the universe. Most of the rest is hydrogen.

This gas is very special. It can act like a liquid. When it gets very cold, it can climb up walls. It can even leak out of a cup.

This gas is very stable. It stays together well. It is the second simplest thing in the world. It is a very cool part of our world.

Helium-4 is a very common part of our world.

It is the main type of helium found on Earth. Its center, or nucleus, has two protons and two neutrons. It also has two electrons spinning around it. This makes it the second simplest atom.

Most helium-4 was made during the Big Bang. This was the start of our universe. It makes up about one quarter of all matter in space. On Earth, we get it from heavy elements in the ground. These elements give off helium-4 through a way called alpha decay.

Helium-4 is very stable. This means its parts stay together very well. This stability helps stars turn hydrogen into helium.

It also makes helium very calm. It does not like to react with other things.

When helium-4 gets very cold, it acts in a strange way. It becomes a superfluid. This is a liquid that flows without stopping. If you put it in a cup, it can climb the sides. It can even crawl out of the cup!

Helium-4 is a very special kind of helium. It is a stable isotope, which means its parts stay together very well.

This type of helium is much more common than any other kind. In fact, it makes up almost all the helium we find on Earth. It is also a huge part of our whole universe. About one quarter of all ordinary matter in space is helium-4. Most of everything else in the universe is just hydrogen. This makes helium-4 one of the most important building blocks in existence.

To understand how it works, we must look inside the atom. The center, called the nucleus, has two protons and two neutrons. Around this center, two electrons spin in a cloud.

This setup is very steady because the particles are in pairs. The two protons and two neutrons follow special rules. They fill up their spaces in a way that is very calm. This is called being doubly magic. This special arrangement makes the atom extremely stable and hard to break apart.

Scientists have learned a lot about where helium-4 comes from. Most of it was made during the Big Bang. This was the very beginning of our universe. This early helium is called primordial helium. Most of it escaped from Earth when our planet was first forming.

Today, we find it in the Earth's crust. It is made when heavy elements break down through alpha decay. This process releases helium-4 from the rocks in the ground.

There are many interesting facts about its size and behavior. The nucleus is very tiny, about 1 femtometer wide.

Scientists even used special atoms with a muon to measure it. They found the size is about 1.67824 femtometers. Helium-4 also has very strange habits when it gets cold. If you cool it below a certain point, it becomes a superfluid. This is a liquid that can flow in amazing ways. It can even climb up the sides of a cup to escape.

You can see how helium-4 links to the stars above us. In the Sun, stars turn hydrogen into helium-4 through fusion. This happens because helium-4 is so much easier to make than other atoms.

Because it is so stable, it stays together during these huge star reactions. This stability also makes helium very calm in other ways. It does not like to react with other elements. This is why helium is used in many things where we need a gas that stays quiet.

Helium-4 is a stable isotope of the element helium. It is the most abundant form of helium found in nature. In fact, it makes up virtually all the helium found on Earth. This isotope is also a massive component of the entire universe. It accounts for about one quarter of the ordinary matter in the universe by mass. Most of the remaining matter is hydrogen.

To understand helium-4, we must look at its internal structure. The atom consists of a nucleus surrounded by an electron cloud. The nucleus contains two protons and two neutrons. Around this nucleus, two electrons orbit in a cloud. This setup makes helium-4 the second simplest atom, following only hydrogen. Because it has an extra electron, calculating its exact movement is a complex three-body problem. Scientists use numerical approximations to estimate its size and ionization energy. The nucleus is incredibly small, measuring about 1 femtometer in scale.

The stability of helium-4 is truly remarkable. Scientists describe its nucleus as being "doubly magic." This means the two protons and two neutrons are arranged in a very stable way. They occupy specific quantum mechanical levels called 1s orbitals. In these orbitals, the particles exist in pairs. Each pair cancels out the other's intrinsic spin. This specific arrangement is energetically extremely stable. Adding even one more particle would require more energy than is available. This is why no nucleus with five nucleons is stable.

This internal stability affects how helium behaves in the world. The stable electron cloud makes helium chemically inert. This means it is the least reactive of all elements. It also explains why helium atoms do not interact much with each other. This lack of interaction results in the lowest melting and boiling points of all elements.

Helium-4 has a fascinating history tied to the beginning of time. Most helium-4 in the universe is considered primordial helium. This means it was produced during the Big Bang. While stars also produce helium-4 through nuclear fusion, the Big Bang provided the largest amount. On Earth, however, primordial helium is mostly absent. It escaped our planet during the high-temperature phase of Earth's formation. Today, most helium-4 on Earth comes from alpha decay. This happens when heavy elements in the Earth's crust break down.

When helium-4 is cooled to extreme temperatures, it shows strange properties. If liquid helium-4 is cooled below a specific point, it becomes a superfluid. A superfluid is a liquid that flows with almost no friction. It behaves very differently from ordinary liquids. For example, a thin Rollin film can form on the surface. This film can actually climb the sides of an open vessel. This causes the liquid to escape the container. Some scientists theorize that at 0.2 K and 50 atm, it may become a superglass. A superglass is a solid that still shows superfluid behavior.

The stability of helium-4 also shaped the composition of our universe. During the Big Bang, free protons and neutrons were available. As the universe cooled, these particles fused into nuclei. Because helium-4 is so stable, it consumed nearly all the free neutrons. This left very few neutrons to form heavier atoms like lithium or boron. This process also explains why the universe has a specific ratio of hydrogen to helium. Today, that ratio is about three parts hydrogen to one part helium-4 by mass.

Finally, helium-4 is central to how stars work. In the Sun, hydrogen is converted into helium-4 through fusion. This happens because creating helium-4 is highly energetically favorable. It is much easier to produce than helium-3 or other elements. Because the Big Bang produced so much helium-4, it left little energy to make heavier elements immediately. Most heavier elements, including those needed for rocky planets and life, had to be made later in stars. These stars had to be hot enough to fuse helium into heavier elements like carbon.