Atoms- Smallest Unit of Matter - Online Tutor, Practice Problems & Exam Prep

Atoms, the smallest units of matter, consist of protons, neutrons, and electrons. The atomic number defines an element by the number of protons, while the mass number is the total of protons and neutrons. Electrons occupy energy shells, with the outermost being the valence shell, crucial for chemical bonding. The octet rule states that atoms are more stable when their valence shells are full, influencing their reactivity. Key elements in life, represented by CHNOPS (carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur), form the basis of biological structures and functions.

Atoms- Smallest Unit of Matter

In this video, we're going to begin our lesson on atoms, which are the smallest unit of matter. Now the term matter is used by scientists to refer to anything that takes up space and has mass. This includes all living organisms like me and you, but also non-living things too like rocks, oceans, and the device that you're watching this video through. Pretty much anything that takes up space and has mass will be matter. Matter is really, really broad and it's going to be at the top here of our lesson for that reason.

It includes living and non-living things. Now all matter, regardless of if it's living or non-living, is going to be made up of at least one chemical element, and that's exactly what we're saying right here. It's going to be made up of at least one chemical element. Now the term chemical element is defined as a pure substance that's made up of only one type of atom. And so, over here in our image, you can see that all matter is made up of at least one chemical element and chemical elements are made up of atoms.

The atom can therefore be defined as the smallest unit of an element. Now, because atoms make up elements and chemical elements make up matter, we can also define the atom as the smallest unit of matter and that's exactly what we're saying right here and up above in our title. Once again, atoms are going to make up both living and non-living matter. So let's take a look down below at our example image to get a better idea of some of these concepts. Notice on the far left over here, we're showing you an image of a diamond and of a honeybee on this plant.

Now, the diamond and the honeybee, because they both take up space and have mass, are both considered types of matter. Now the diamond of course is going to be non-living matter whereas the honeybee and the plant are going to be living matter. Now if we zoom into the diamond here, which you can see is the diamond structure that we're showing you over here, which is made up of all of these Cs that we see here. And these Cs represent a type of element and so it's made up of just one type of element, which is the element carbon, which is abbreviated with just a C. Now if we zoom into one of these chemical element symbols, one of these Cs, what you'll see is that it is a carbon atom.

And so here on the far right, we're showing you a representation of a carbon atom. Now in our next video, we're going to talk more about the structures and properties of atoms. But for now, you should notice that non-living matter like diamond is going to be made up of at least one chemical element and the smallest part of a chemical element is going to be the atom itself. Similarly, down below with the honeybee and the plant, when we zoom into one of its chemical structures, you can see that it's going to have a sugar like, for example, glucose is a sugar that can be found in these living organisms. And what you'll notice is that this glucose structure over here actually has multiple types of elements.

In fact, it has 3 types of elements. It has the same carbon element as the diamond, but then it also has the element oxygen and the element hydrogen, and you can see those throughout this glucose structure here. Now if we zoom into just one of the chemical element symbols of hydrogen here, what you'll see is that the smallest unit of this element is a hydrogen atom. And so this is the representation of the hydrogen atom. Once again, we'll talk more about the components of the atom and the properties of the atom moving forward in our course.

But for now, this here concludes our introduction to how atoms are the smallest unit of matter. And once again, the biggest takeaway is that all matter is going to be made up of chemical elements and the smallest unit of a chemical element is the atom. So I'll see you guys in our next video.

Atomic Structure

In this video, we're going to talk about atomic structure or the structure of atoms. Now, atoms are made up of 3 subatomic particles, each with their own characteristic charge, mass, and location within the atom. Notice over here we have this table that gives you information on the 3 subatomic particles that make up an atom. And so those 3 subatomic particles are protons, neutrons, and electrons. When it comes to the electric charge of a proton, it's actually going to be plus one, so it has a positive charge, and you can think that the p here in proton is for the p in positively charged.

When it comes to the electric charge of the neutron, the neutron is going to be, as its name implies, neutral, meaning that it has a neutral electric charge of 0, and so its electric charge is going to be 0. When it comes to the electron and its electric charge, it's going to have a negative one electric charge. And so the way that you can think about it is electron kinda sounds like getting electrocuted, and getting electrocuted is definitely not something positive, it's something negative, and that's how you can remember that it's going to have a negative one charge. When it comes to the mass of subatomic particles, they are so incredibly small that it doesn't really make a lot of sense to measure their mass in pounds or ounces or kilograms or grams even. They're so small that scientists have come up with a new unit to measure their mass, and that unit is called the atomic mass unit or AMU for short.

Protons have an atomic mass unit of 1. Neutrons also have an atomic mass unit of 1. However, electrons are going to be different. Electrons have a mass that is so incredibly small that it's practically negligible, meaning that we can pretty much ignore its mass and just round it off to say that it is 0. And so we can go ahead and say that the electron has an atomic mass unit of 0.

In terms of the location of these subatomic particles within the atom, you can see that the proton is found within the nucleus of the atom. The neutron is also found within the nucleus of the atom. However, the electrons, once again, are going to be different. Instead of being found within the nucleus, the electrons are going to be found orbiting the nucleus or revolving around the nucleus. If we take a look at our image over here, you can see that we're showing you the image of a carbon atom right here.

Notice that the nucleus is indicated with the purplish background. Within the nucleus, we have these positively charged protons that look like this, and then we also have these neutral, gray, circles that represent the neutrons, and both the protons and the neutrons are found packed within the nucleus of the atom, just like what we see here. However, notice that the electrons, which are these little, blue circles, are not found within the nucleus. Instead, the electrons are going to be found orbiting the nucleus in these electron shells that we see here. We'll talk more about these electron shells as we move forward in our course, but for now, what you should know are the subatomic particles, our protons, neutrons, and electrons, you should know their characteristic electric charge, their characteristic atomic mass unit, and the location of each subatomic particle.

This here concludes our introduction to atomic structure and as we move forward, we'll be able to get some practice. So I'll see you all in our next video.

Atoms- Smallest Unit of Matter Example 1

Alright. So here we have an example problem that wants us to fill in the sentence here using one of these 5 potential answer options down below. And it says that negatively charged particles of atoms with almost no mass are called either electrons, protons, neutrons, ions, or polymers. Now, so far, at this point in our course, we have not yet introduced ions or polymers. However, later in our course, we definitely will talk about these two terms, but because we have not yet introduced these two terms, we should have been able to figure out that these 2 are not going to be the correct answer for this problem.

So now we're between either electrons, protons, or neutrons, which are the 3 subatomic particles of a typical atom. Recall that the 'p' in protons can remind us that this subatomic particle is positively charged. So you can think the 'p' in protons is for the 'p' in positively charged. And so, because protons are positively charged, they are not going to be negatively charged, and so we can eliminate answer option b. And also recall that neutrons, as their name implies, are neutral, and neutral means that it has a net charge of 0 and so it will not be negatively charged; it will have a charge of 0.

So once again, we can eliminate neutrons, and of course this only leaves the electrons which is the correct answer for this example problem. And so electrons are negatively charged and recall that electrons kinda sounds like getting electrocuted, and getting electrocuted is something negative, and so that can remind us that electrons are negatively charged. And also, electrons have almost no mass, and so we can pretty much say that their mass is about equal to 0. And so, we can go ahead and, indicate that a here is the correct answer to this example problem. And that concludes this example, so I'll see you guys in our next video.

A proton ___________:

• A. Has one positive charge.
• B. Has one AMU.
• C. Is found in the nucleus of the atom.
• D. Only a and b are true.
• E. a, b, and c are true.

Elements of Life

In this video, we're going to talk about the elements of life. And so what's interesting to note is that of all of the known elements that exist in the universe, only a small subset of those elements is found in living organisms. Now the periodic table of elements, which I'm sure you guys have probably heard of before in your previous courses, is a table that arranges all of the known elements that exist based on their chemical properties. And so if you take a look down below at our image, what you'll notice is we're showing you a periodic table of elements showing you all of the known elements that exist. Now once again, living things do not utilize all of these elements.

Instead, they only utilize a small subset of them. In fact, about 97% of the mass of most living organisms, which is the vast majority of the mass, is made up of just 6 elements, which are carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. And if you take the chemical symbols for each of these elements, it spells the word CHNOPS. And so if you can remember CHNOPS, then you'll be able to remember these 6 elements that make up the vast majority of most living organisms. Because these 6 elements make up the vast majority of most living organisms, they are referred to as bulk elements, which we're showing you down below here in the periodic table.

So notice that the bulk elements are highlighted in blue. And so you can see the positions of these 6 elements that make up the vast majority of life: hydrogen, carbon, nitrogen, oxygen, phosphorus, and sulfur. And so, if you arrange them in the right way, it'll spell out that word CHNOPS. Now what you'll also notice is that we've got these other elements that are highlighted in this yellowish color, and these are referred to as the trace elements.

And so as the name implies with trace elements, these are required for life. However, they're only required in trace amounts or in very small amounts. And so if you take a look down below, notice once again that the trace elements that are required for life, however they're required in very, very small amounts, are highlighted in yellow throughout our table here. And so you don't need to memorize all of these trace elements. Don't worry about doing that.

Instead, what you should be aware of is that there are some trace elements that are required in small amounts, and you should be more familiar with the bulk elements, which again, you can remember just by remembering CHNOPS. And so this here concludes our lesson on the elements that are required for life and we'll be able to get some practice as we move along through our course. And so I'll see you all in our next video.

Atomic Properties

Alright. So here in this video, we're going to talk about some atomic properties. Each atom of an element has unique properties, and we're going to talk about 3 specific properties that you all should be familiar with. Now, the very first property that you all should be familiar with is the atomic number.

The atomic number is defined pretty simply. It's a straightforward idea. All it is is the total number of protons in the nucleus of an atom. To get the atomic number, count up the total number of protons, and that's it. The atomic number, or the total number of protons, is actually what defines each element.

If we change the total number of protons in the nucleus of an atom, then we change the element that it falls under. However, if we change the other subatomic particles like neutrons or electrons, then we do not change the element. Only changing the number of protons or only changing the atomic number will change the element, and that's why the atomic number, or the number of protons, defines each element. Let's take a look at our example down below to clear some of this up. We're taking a look at the atomic properties of a carbon atom, more specifically, the carbon atom that we're showing you right over here.

If we want to determine the atomic number, which is once again just the number of protons in the nucleus, all we need to do is count up the total number of protons in this nucleus over here. When we do that, what we'll see is that there are a total of 6 protons in the nucleus, which means that the atomic number of this atom is 6. The protons are here in red, and we're just counting up the number of red circles here, and there are 6 of them, which is why the atomic number is 6. So that's pretty straightforward.

If we were to add a 7th proton in here, then we would be changing the element, and it would no longer be carbon. Instead, it would be nitrogen. The number of protons in the nucleus defines the element. If we were to add another neutron here, pretend this were a gray circle, if we were to add another neutron then it would still be a carbon atom. If we were to add another electron, revolving around the nucleus, then it would also still be a carbon atom, and so, the number of electrons and neutrons do not affect the type of element that it is.

Moving on, what we have next is the mass number, and the mass number is also a pretty straightforward idea. It's really just the mass of the nucleus of a single atom.

If we want to take the mass of the nucleus, then we need to consider the subatomic particles that are inside of the nucleus, which we know are both protons and neutrons as well. The mass number is going to be the total number of protons and neutrons found in the nucleus. Once again, let's take a look at our example down below. We already know the number of protons, and so if we count the number of neutrons, the number of gray circles here in the nucleus, what you'll count is that there are a total of 6. So, to calculate the mass number, all we need to do is total up the two. We have 6p+6neutrons=12, and so this is going to be the mass number that we just defined up above here.

Last but not least, what we have here is the atomic mass, which is also sometimes referred to as the atomic weight.

The atomic mass or atomic weight sounds kind of similar to this mass number idea, and really they are very similar. However, there's one big difference, and this is the idea that the atomic mass or atomic weight, instead of being the mass of the nucleus of 1 atom, it's actually going to be an average total mass of all of the atoms of an element. It is an average, whereas the mass number is not an average; it's the mass of just one atom. Now, in your textbooks, you'll see a periodic table view that looks somewhat like this for the elements. The first number you'll see here is 12.011. This number here is what we refer to as the atomic mass or atomic weight that we just talked about, which is once again an average total mass of all of the atoms of an element, which is why it looks like a strange number here with the 0.011. We'll be able to understand this idea of atomic mass or atomic weight much better later in our course once we start talking about isotopes.

You'll also note that the atomic number tells us the total number of protons in the nucleus, which we know is 6 here for the carbon atom. You'll also note that the chemical symbol is always going to be shown here. For carbon, the chemical symbol is C, and the element name is usually provided as well which is carbon. This here concludes our introduction to these atomic properties of atomic number, mass number, and atomic mass or atomic weight.

We'll be able to get some practice applying these concepts moving forward in our course, so I'll see you all in our next video.

Atoms- Smallest Unit of Matter Example 2

Alright. So here we have an example problem that wants us to complete the sentence here using one of these 5 potential answer options down below. And it says that the atomic number of an element is equal to the number of neutrons only, neutrons plus electrons, protons plus electrons, protons only, or protons plus neutrons. Now, of course, we know from our last lesson video that the atomic number is going to be exactly equal to the number of protons only that are found in the nucleus. And so this here is our atomic number, and it is the correct answer to this example problem.

Now, of course, protons plus neutrons might sound familiar, but that's because this is referring to the mass number or the mass of the nucleus of an atom. But it's not the same thing as the atomic number, so that's why it's not correct. The protons plus electrons are going to dictate the net charge of the atom because remember protons are positively charged and electrons are negatively charged, and so the balance of protons and electrons, which are oppositely charged, is going to dictate the overall net charge of the atom. But once again, option b here is not going to be the atomic number. And then neutrons only and neutrons plus electrons, they, once again are not going to be the atomic number.

So that concludes this example problem and I'll see you in our next video.

The average oxygen atom has a mass number of 16 and an atomic number of 8. This means that the number of neutrons in this oxygen atom is:

• A. 24.
• B. 8.
• C. 16.
• D. 4.
• E. 2.

Electron Orbitals & Energy Shells

In this video, we're going to continue to talk about atoms by focusing on their electron orbitals and energy shells. Now, electron orbitals are really defined as three-dimensional regions around the nucleus of an atom where electrons can be found. Although electron orbitals are three-dimensional regions, they can still be envisioned in two dimensions as energy shells. In our course, we're mainly going to focus on the energy shell aspect. You'll learn more about the three-dimensional shapes of electron orbitals in a chemistry class.

Let's take a look at our example image here of the carbon atom on the far left to get a better understanding of this idea of energy shells. What you'll notice is that the chemical symbol in the middle represents the nucleus of this carbon atom, but revolving around the nucleus are black circles, two of them, representing energy shells. Energy shells are just the two-dimensional representation of the electron orbitals, which are three-dimensional regions. These energy shells contain electrons, depicted as blue circles that orbit around the nucleus of the atom. Typically, an atom could have multiple energy shells as illustrated in our image below.

If we focus on the carbon atom, notice that it has two energy shells. The one that is closer to the nucleus and a second energy shell further from the nucleus. The energy shells closer to the nucleus are lower in energy than those more distant from the nucleus. Distant shells, being higher in energy, are more reactive. These higher energy shells are what scientists focus most of their attention on when looking at chemical bonds, which we'll discuss more in another video. The energy shell furthest from the nucleus is the highest in energy and the one that tends to form chemical bonds. This leads us to the concept of valence electrons, defined as the electrons in the outermost energy shell, also known as the valence shell. Electrons in the valence shell, in this case, the furthest shell, are termed valence electrons, and are higher in energy and more reactive. The other electrons closer to the nucleus are not as high in energy and are less likely to form chemical bonds with other atoms.

Below the atom, the chemical symbol is displayed. To the top left of the chemical symbol, we can show the mass number, which represents the total number of protons and neutrons. To the bottom left of the chemical symbol, the atomic number, which is the total number of protons in the nucleus. For the carbon atom shown here, it has 6 protons in its nucleus, symbolized by the letter C, and also has 6 electrons, maintaining a neutral net charge since the number of protons balances out with the number of electrons.

All the atoms we are showcasing here also have a neutral net charge. The first energy shell always holds a maximum of 2 electrons and the second energy shell holds up to 8 electrons. Upon examining the carbon atom further, the first energy shell holds 2 electrons and any additional electrons are in a different energy shell. Similarly, the hydrogen atom, which has an atomic number of 1, meaning it has one proton and no neutrons, has just one electron requiring only one energy shell. The nitrogen atom, having 7 protons and electrons, fills its first energy shell with 2 electrons, with the remaining electrons occupying the second shell which holds up to 8 electrons.

The oxygen atom, with an atomic number of 8 and a mass number of 16, indicating 8 neutrons, positions its first two electrons in the first energy shell, with the other electrons in the second shell holding 6 electrons. The phosphorus atom, with an atomic number of 15 and a mass number of 31, and the sulfur atom, with an atomic number of 16 and a mass number of 32, follow similar electron arrangements with their first and second energy shells.

This concludes our lesson on electron orbitals and energy shells, and we will be able to get some practice applying these concepts in our next few videos. I'll see you in the next one.

How many valence electrons does an atom with five total electrons have?

• A. 5.
• B. 7.
• C. 3.
• D. 2.
• E. 1.

Which of the following is true about electron energy shells?

• A. They represent regions around the nucleus in which the electrons orbit.
• B. The shells closest to the nucleus contain electrons with higher energy.
• C. They contain electrons of the same energy.
• D. a and b only.
• E. a and c only.

Octet Rule

In this video, we're going to introduce the Octet Rule. Now, the Octet Rule is really just a rule of thumb that says that atoms are more stable and less reactive when their valence shells are fully occupied. Recall from our last lesson video that the first energy shell will hold up to a maximum of just 2 electrons, but the second energy shell will hold up to a maximum of 8 electrons, and really this 8-electron maximum is where this octet is coming from with the octet rule. Most of the simple atoms that we'll be talking about in our biology course are going to apply to this octet rule. But really, the main takeaway here of the octet rule is that atoms are going to be less reactive when their outer valence shells are fully occupied.

So let's take a look at our image down below to get a better idea of this octet rule. Notice that here in the middle what we have is an electron. These little blue circles that you see throughout our image represent electrons, and this represents some electron that wants to react. On the left, we have an atom, and on the right, we have another atom. Notice that the dinner table here, with the Thanksgiving turkey, represents the nucleus of these atoms, and revolving around the nucleus what we have are the electrons. We're specifically focusing on the second energy shell here which we know holds up to a maximum of 8 electrons. Notice that the electrons that have an open slot in their energy shells are going to be more likely to react.

You can see that this atom over here, because it does have an open slot that's available, says, "Yeah, there is a spot for you here," and so it will react with other electrons from other atoms. However, this atom over here, notice, has a full octet of electrons, and because it is full, it says, "Nope, we're full," and they do not react with other electrons from other atoms. So, the idea once again is that atoms are going to be less reactive when their valence shells are full, like this one has a full octet in its second shell, so it's going to be much less reactive and it will not react with other electrons that want to react. That's the main takeaway here of the octet rule, and we'll be able to get a little bit of practice in our next few videos. So, I'll see you guys there.

Atoms- Smallest Unit of Matter Example 3

Alright. So here we have an example problem that says according to the octet rule, electron distribution in each shell of a neutral nitrogen atom with an atomic number of 7 is which one of these 4 potential answer options down below? Where the first number of each answer option suggests the total number of electrons in the first energy shell, and the second number of each answer option represents the total number of electrons in the second energy shell. And so really what we need to do is draw ourselves a little sketch of a neutral nitrogen atom, which once again has an atomic number 7. So let's go ahead and say that this green circle here represents the nucleus of our nitrogen atom, which once again we know has an atomic number of 7, so we know that it has 7 positively charged protons in its nucleus.

But then it tells us that the nitrogen atom is neutral, which means that it's going to have an overall net charge of 0, which means that the positively charged protons are going to be balanced out perfectly with the number of negatively charged electrons. So if there are 7 positively charged protons there must be 7 negatively charged electrons in order to make this nitrogen atom neutral. So we have to draw a total of 7 electrons. Considering that we can go ahead and draw our first energy shell, and we know that the first energy shell holds a maximum of 2 electrons. So we can go ahead and fill this first energy shell here with 2 electrons as we see here, and then the other electrons need to go into the next shell.

So, we can go ahead and draw our second energy shell and of course, we can put the remaining electrons here. So we know that there must be a total of 7 electrons. We've already got 2, so we got to put 5 more in the second shell. So we can go ahead and put 1, 2, 3, 4, and 5 electrons in this outer shell. So once again, there's a total of 7 electrons here that balance out the 7 protons, which makes this nitrogen atom neutral.

And so now all we need to do is take a look at the answer options and once again we can see that the first energy shell here has a total of 2 electrons not one electron as option a and option d indicate. So we can go ahead and eliminate answer option a and answer option d just based on that. However, when we look at answer option b and answer option c notice that they both suggest the first energy shell has 2 electrons, which once again is correct. We can see the first energy shell does have 2 electrons. So then we need to look at the second number which is really how these two answers differ and you can see that the second energy shell when you count them up there is a total of 5 electrons not 4 electrons.

So we can go ahead and eliminate answer option b here. We can eliminate answer option b and go ahead and indicate that answer option c here, that is the correct answer for this example problem. And the reason for that is once again, the 2 here indicates the number of electrons in the first energy shell, which you can see there's one here and the other is right here. And then the second number of 5 indicates the number of electrons in the second energy shell. And, once again there are 5 when you count those up.

So c here is the correct answer to this example, and I'll see you guys in our next practice video.

A neon atom (Ne) is unreactive for which of the following reasons?

• A. It has 7 valence electrons.
• B. It has 8 valence electrons.
• C. Its valence shell is full of electrons.
• D. It has 20 valence electrons.
• E. b and c only.

How many electrons does an Oxygen atom need to fulfill the octet rule by filling its valence shell?

• A. 8.
• B. 4.
• C. 1.
• D. 2.
• E. 6.

Here’s what students ask on this topic:

What is the atomic structure of an atom?

An atom consists of three main subatomic particles: protons, neutrons, and electrons. Protons, which have a positive charge, and neutrons, which are neutral, are located in the nucleus at the center of the atom. Electrons, which have a negative charge, orbit the nucleus in regions called electron shells or energy levels. The number of protons in the nucleus defines the atomic number of the element, while the sum of protons and neutrons gives the mass number. Electrons in the outermost shell, known as valence electrons, play a crucial role in chemical bonding and reactivity.

What are the key elements in living organisms?

The key elements in living organisms are carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S), collectively remembered by the acronym CHNOPS. These elements make up about 97% of the mass of most living organisms. Carbon is the backbone of organic molecules, hydrogen and oxygen are essential for water and organic compounds, nitrogen is a key component of amino acids and nucleic acids, phosphorus is found in nucleic acids and ATP, and sulfur is present in some amino acids and vitamins.

What is the octet rule in chemistry?

The octet rule is a principle that states atoms are more stable and less reactive when their outermost electron shell, or valence shell, is fully occupied by eight electrons. This rule applies mainly to the main-group elements. Atoms will often gain, lose, or share electrons to achieve a full valence shell, leading to the formation of chemical bonds. For example, in a water molecule (H₂O), oxygen shares electrons with hydrogen atoms to complete its valence shell, resulting in a stable configuration.

How do protons, neutrons, and electrons differ in terms of charge and mass?

Protons have a positive charge (+1) and a relative mass of 1 atomic mass unit (AMU). Neutrons are neutral, with no charge, and also have a mass of 1 AMU. Electrons have a negative charge (-1) and a much smaller mass, approximately 1/1836 of a proton's mass, which is often considered negligible. Protons and neutrons are located in the nucleus, while electrons orbit the nucleus in energy shells.

What is the significance of the atomic number and mass number?

The atomic number of an element is the number of protons in the nucleus of an atom, which defines the element. For example, carbon has an atomic number of 6, meaning it has 6 protons. The mass number is the total number of protons and neutrons in the nucleus. For instance, a carbon atom with 6 protons and 6 neutrons has a mass number of 12. The atomic number determines the element's identity, while the mass number provides information about its isotopes.