The Atom (Simplified): Study with Video Lessons, Practice Problems & Examples

An atom is the smallest unit of an element, consisting of a nucleus containing protons and neutrons, with electrons orbiting around it. The nucleus is held together by nuclear force, which counteracts the electrostatic force that tries to separate the positively charged protons. For a stable nucleus, the nuclear force must be greater than the electrostatic force. Understanding these forces is crucial for grasping atomic stability and the behavior of elements in chemistry.

The Atom (Simplified) Concept 1

The atom represents the smallest part of an element and is the basic fundamental unit in chemistry. Now it is comprised of four major parts. The first part is the nucleus. It serves as the center of an atom that possesses two subatomic particles of neutrons and protons. Here we have an image of the atom below. We're going to say here that this orange band represents the nucleus. Inside of it, we have these red and blue balls which represent our neutrons and our protons respectively. Now the neutrons, these are the subatomic particles that carry no charge and are found within the nucleus. The protons are the subatomic particles that carry a positive charge and are also found within the nucleus. Outside of the nucleus, we have our electrons. The electrons are the subatomic particles that carry a negative charge, and they spin around the nucleus. So these electrons here are rotating around the nucleus itself. Now what you need to realize here is that this image of the atom is not drawn to scale. The electron cloud, which is where we find the electrons, is about, well, actually not 1,000, 1,000,000 times larger than the nucleus. So in actuality, the nucleus would be this little dot, and the atom would be this entire thing. The nucleus would be incredibly, incredibly small when compared to the entire volume of the atom itself. So just keep that in mind. Although the nucleus contains two subatomic particles, it itself is very, very small.

The Atom (Simplified) Example 1

So if we take a look at this example question, it says, which of the following statements is true? First, protons and electrons have charges of the same magnitude, but opposite signs. Well, we said that protons are positively charged and electrons are negatively charged, so they definitely have opposite signs. We could think of a proton as having a plus one charge and an electron having a minus one charge. So their magnitudes, basically the number assigned with the charge, are the same. They're 1. Right? Plus 1 minus 1. So the first statement is true.

Now let's see why the other statements are not true. Here, the number of protons must equal the number of neutrons within the atom. Alright. So if we look up above, we said that we had 5 of these protons within the nucleus, and we had 6 of these neutrons within the nucleus. In this example of the atom, we can clearly see that the number of protons and neutrons are not equal. Now there are going to be times when a certain atom may have the same number of protons and neutrons, but that's not always a given. So this statement is not always true.

The atom is best described as a uniform sphere of mass in which electrons are embedded. Alright. So if we look at the atom itself, first of all, I said that the nucleus, I blew it up to show what's within it. But in reality, the nucleus is extremely small when it comes to the atom. Okay? It's very, very small in relation to the whole volume of the atom. We're also going to say here that the word uniform is what gives this away as being wrong. The atom isn't uniform. It's not the same throughout. There's a part of the atom, that's the nucleus, which is different from other parts of the atom which are not the nucleus. Within the atom, we have electrons swirling around the nucleus. Okay, so the composition is not exactly the same everywhere. There are unique parts to the atom in different places. So this would mean that it's not a uniform sphere of matter, it has different parts to it.

The volume of the nucleus is a very large fraction of the total volume of the atom. So, this is saying the exact opposite of what I said. The nucleus itself is extremely small. In the image above, I've blown it up to show it better, to show that within the nucleus are housed protons and neutrons. In reality, it's super small and hard to see all these protons and neutrons. So this is false. It's a very small fraction of the total volume of the atom.

Now that we've done this example question, let's continue onward with our discussion of the nucleus of the atom.

The Atom (Simplified) Concept 2

So we've talked about the nucleus. It's at the very center of the atom. It's extremely small in relation to the total volume of the atom, and it contains protons and neutrons. Now when it comes to our nucleus, there are forces at work that help to keep that nucleus together, but there are also forces at work that try to pull it apart. Now we're going to say within the nucleus, there are these two major forces that characterize the behavior between protons and neutrons. Now we have what's called our nuclear force, the force within the nucleus that pulls together protons and neutrons. The way we have to think about it is, in chemistry we say that opposites attract. If you have opposite charges, you attract one another. Same charges repel one another. If you think about it, you have positively charged protons around. If you get them close enough to each other, because they have the same charge, they're going to want to repel each other. The way we prevent this from happening is with the neutrons. The neutrons have no charge for a reason. They kind of act as the glue that keeps the nucleus together. We'll go into greater detail several chapters from now when we cover nuclear chemistry and talk more in-depth about nuclear force and electrostatic force, but just realize here that the neutrons kind of act as the glue that keeps together the protons, which have the same charge. All these protons with positive charges don't want to be next to each other. Now besides the nuclear force, we have the electrostatic force. The electrostatic force is the force within the nucleus that pulls apart protons and neutrons. So it's just basically this balancing act between the two forces.

If nuclear force is greater than electrostatic force, it has an effect on the nucleus. If electrostatic force is greater than nuclear force, it has an effect on the nucleus. Now we're going to say for a stable nucleus that is held together. Remember the force that's holding it together is the nuclear force. It keeps everything together. The electrostatic force is what's trying to pull things apart. If you want to have a stable nucleus that is together, you want to make sure that your nuclear force is greater than your electrostatic force. So just realize again the four primary parts of the atom, and realize that within the nucleus it's not a done deal that it's going to hold together and your atom will exist. You have these two forces that are at odds with one another, and if one is greater than the other, it can either mean the nucleus is held together or it's broken down and totally destroyed. Now that we've understood the basic parts of the atom, now that we've discussed the nucleus, let's continue on to our next question.

The Atom (Simplified) Example 2

So if we take a look at this example question, it says, which of the following statements is false? So we're looking to see what is not true.

• A. The nucleus is composed of protons and neutrons. Well, we know that's true, we've talked about that at the very beginning. The nucleus has protons and neutrons, and spinning around the nucleus are the electrons. So this is true.
• B. When the nuclear force is less than the electrostatic force, then the nucleus will not remain intact. Alright. So let's go up above. We said that the nuclear force holds it together, the electrostatic force tries to pull it apart. We said that the nucleus will be held together as long as the nuclear force is greater than the electrostatic force. But what happens if that's not true? Well, if the nuclear force is less than the electrostatic force, it makes sense that the nucleus would not be held together. So this is also true. Right? Because we're saying the opposite of what we said up above.
• C. The nucleus has an overall neutral charge. Well, the nucleus houses what? Positive protons and neutral neutrons. So I'm just doing shorthand, proton \( p \) has a positive charge. Neutrons \( n \) have no charge. Usually, we denote that with a 0 or circle here to show that it has no charge. Think about it. We have positive charges only within the nucleus. There's no other charges within it. So the nucleus overall should have a positive charge, not a neutral charge. So this is false.
• D. When the nuclear force is greater than the electrostatic force, then the nucleus will remain intact. Well, that's exactly what we said up above. If the nuclear force is greater than the electrostatic force, then the nucleus is stable and will be held together. So just remember, when it comes to the nucleus, we have these two forces that are opposing one another trying to be the primary force, and this can either lead to the stability of the nucleus or have it fall apart.

Here’s what students ask on this topic:

What are the main parts of an atom and their functions?

An atom consists of three main parts: the nucleus, protons, and electrons. The nucleus, located at the center, contains protons and neutrons. Protons are positively charged particles, while neutrons carry no charge. The nucleus is held together by nuclear force, which counteracts the electrostatic force that tries to separate the positively charged protons. Electrons are negatively charged particles that orbit the nucleus in an electron cloud. The electron cloud is significantly larger than the nucleus, making the nucleus very small in comparison to the entire atom. Understanding these components is crucial for grasping atomic structure and behavior in chemistry.

How do nuclear force and electrostatic force affect the stability of the nucleus?

Nuclear force and electrostatic force play crucial roles in the stability of the nucleus. Nuclear force is the attractive force that pulls protons and neutrons together, acting as the 'glue' that holds the nucleus intact. Electrostatic force, on the other hand, is the repulsive force between the positively charged protons. For a nucleus to be stable, the nuclear force must be greater than the electrostatic force. If the electrostatic force exceeds the nuclear force, the nucleus can become unstable and may break apart. This balance between the two forces determines whether an atom's nucleus remains stable or disintegrates.

Why are neutrons important in the nucleus of an atom?

Neutrons are crucial in the nucleus because they help stabilize it. Unlike protons, which are positively charged and repel each other due to electrostatic force, neutrons carry no charge. This neutrality allows them to act as a buffer between protons, reducing the repulsive forces and helping to hold the nucleus together through nuclear force. Without neutrons, the electrostatic repulsion between protons would likely cause the nucleus to break apart. Therefore, neutrons play a vital role in maintaining the stability of the nucleus.

How does the size of the nucleus compare to the size of the entire atom?

The nucleus is extremely small compared to the entire atom. While the nucleus contains protons and neutrons, it occupies a minuscule fraction of the atom's total volume. The electron cloud, where electrons orbit the nucleus, is about 1,000,000 times larger than the nucleus. If the atom were the size of a football stadium, the nucleus would be comparable to a small marble at the center. This vast difference in size highlights the nucleus's compactness relative to the overall atom.

What is the role of electrons in an atom?

Electrons are negatively charged particles that orbit the nucleus of an atom in an electron cloud. They play several crucial roles in an atom. Firstly, they balance the positive charge of protons, making the atom electrically neutral. Secondly, electrons are involved in chemical bonding and reactions. The arrangement of electrons in different energy levels or shells determines how atoms interact with each other to form molecules. Electrons also influence the atom's physical and chemical properties, such as conductivity and reactivity. Understanding the behavior of electrons is essential for studying chemistry and physics.