The Atom - Online Tutor, Practice Problems & Exam Prep

Atoms, the fundamental units of elements, are composed of a nucleus surrounded by electrons. The nucleus, though small relative to the atom's size, contains protons with a positive charge and neutrons with no charge. Electrons, which are negatively charged, orbit the nucleus. The stability of the nucleus is governed by a balance between nuclear force, which binds protons and neutrons, and electrostatic force, which tries to separate them. For a stable nucleus, the nuclear force must be greater than the electrostatic force. Understanding these subatomic particles and the forces at play is crucial for grasping the atom's structure and the principles of nuclear chemistry.

The Atom

Now, the atom represents the smallest part of an element, and it's the basic function of unit. In chemistry, we're going to say that it consists of four major parts. Now, in actuality, there are other parts to the atom, but we're not going to mention them because they're beyond the scope of this class. If you ever decide to go into high levels of chemistry, you'll worry about them then. But for right now, when it comes to general chemistry, let's just worry about these four portions of the atom.

The first part, which is outlined by this orange circle within this image of the atom, it's the nucleus. Now, the nucleus isn't really that large. I've blown it up so that we can see what's inside of it. We're going to say the nucleus represents the center of an atom that possesses the two subatomic particles are neutrons, which we show as red. So these red circles here are our neutrons and our protons, which are symbolized by these blue spheres here.

Now we're going to say the neutrons themselves. They're the subatomic particles that carry no charge and of course are found within nucleus and the protons themselves are the subatomic particles that carry a positive charge and are found within the nucleus. So within this image we have 1, 2, 3, 4, 5 protons and we have 1, 2, 3, 4, 5, 6 neutral neutrons.

Now what's swirling around the nucleus? We have these small little green spheres. These are the smallest subatomic particles, the electrons that carry a negative charge, and of course they spin around the nucleus. So when it comes to our atom itself, it's the smallest part of an atom. It's consisting of four parts. Basically, the nucleus houses the protons and neutrons, with the electrons spinning around the nucleus. We'll go into a greater discussions about how these electrons move in later chapters, but for now just focus on these four primary portions of the atom.

The Atom Example 1

So if we take a look at this example question, it says which of the following statements is true? First, a 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 sides. We could think of a proton as having a plus one charge and an electron having a -1 charge. So their magnitudes, basically the number assigned with the charge, they're the same. They're one, right? Plus 1, -1. So the first statement is true.

Now let's see why the other statements are not true. Here are the number of protons must equal the number of neutrons within the atom. All right, so if we look up above, we said that we had five of these protons within the nucleus, and we had six 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. OK, 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 is 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 swirling around the nucleus, these electrons. OK, so the composition is not exactly the same everywhere. There's 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 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 our housed our protons and neutrons. In reality it would be super super small and hard to see all these protons and neutrons. So this is false. It's 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

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 the nucleus together, but there's 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 the neutrons. The neutrons have no charge for a reason. They kind of act as the glue that keeps the nucleus together. OK, 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 going to the nuclear force, it has an effect on the nucleus. Now we're going to say for stable nucleus that is held together. Remember, the force that's holding it together is the nuclear force. It keeps them. 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, 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 kind of like 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 onward to our next question.

The Atom Example 2

So If we take a look at this example question, it says which 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 in the very beginning. The nucleus has protons and neutrons, and spinning around the nucleus are the electrons. So this is true.

When the nuclear force is less than the electrostatic force, then the nucleus will not remain intact. All right, 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 your nuclear force is less than your electrostatic force, it makes sense that the nucleus would not be held together. So this is also true because we're saying the opposite of what we said up here.

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 it has a positive charge. Neutrons N has 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 is no other charges within it. So the nucleus overall should have a positive charge, not a neutral charge. So this is false.

And then D when the nuclear force is greater than the electrostatic force, then the nucleus will remain intact. Well that's exactly what we set up above. If your nuclear force is greater than your 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 is an atom?

An atom is the fundamental building block of all matter in the universe. It's the smallest unit of an element that retains the chemical properties of that element. At the center of an atom is a nucleus, which contains protons (positively charged particles) and neutrons (particles with no charge). Surrounding the nucleus are electrons, which are negatively charged particles that orbit the nucleus in various energy levels or shells. The number of protons in the nucleus defines the atomic number of an element and determines its place on the periodic table. Atoms can bond with each other to form molecules, which are compounds consisting of two or more atoms held together by chemical bonds. The interactions and combinations of different atoms lead to the vast diversity of materials and substances we observe in the world around us.

What is the difference between an atom and a molecule?

An atom is the smallest unit of an element that retains the chemical properties of that element. It consists of a nucleus containing protons and neutrons, surrounded by electrons that orbit in electron shells. Atoms can exist independently or can combine with other atoms to form various substances.

A molecule, on the other hand, is a group of two or more atoms that are chemically bonded together. Molecules can be formed from atoms of the same element, like $O_2$ (oxygen gas), or from atoms of different elements, like $H_{2}O$ (water). The atoms in a molecule are held together by chemical bonds, such as covalent or ionic bonds, which involve the sharing or transfer of electrons between atoms. Molecules are the smallest units of a compound that can exist while still retaining the compound's unique chemical properties.

What determines the identity of an atom?

The identity of an atom is determined primarily by the number of protons it contains in its nucleus, which is known as the atomic number. Each element on the periodic table is defined by a unique atomic number. For example, hydrogen has one proton, so its atomic number is 1, while carbon has six protons, giving it an atomic number of 6.

Apart from protons, atoms also contain neutrons and electrons. The number of neutrons can vary within atoms of the same element, leading to different isotopes of that element. However, these differences in neutron numbers do not change the fundamental identity of the element.

Electrons, which are negatively charged and orbit the nucleus, do not affect the identity of the atom but do play a crucial role in the chemical behavior and bonding of the atom. The arrangement of electrons in various energy levels or shells determines how an atom interacts with others to form molecules.

How small is an atom?

An atom is incredibly small, typically around 0.1 to 0.5 nanometers in diameter. To put that into perspective, a nanometer is one billionth of a meter. If you were to line up 10 million atoms side by side, they would approximately span the width of a human hair. The exact size of an atom varies depending on the element it represents, as different elements have varying numbers of protons, neutrons, and electrons, which contribute to the atom's size. The smallest atom is that of hydrogen, which has a diameter of about 0.1 nanometers, while larger atoms like uranium can be about 0.3 nanometers wide. However, most of the atom's volume is empty space, with the nucleus, which contains the protons and neutrons, being much smaller than the overall size of the atom, and electrons orbiting this nucleus at relatively large distances.