Understanding Atoms and Ions: Protons, Neutrons, Electrons

In this lesson, we're going to talk about how to calculate the number of protons, neutrons, and electrons in an atom and in an ion. So let's use sodium as an example. And on a periodic table, you might see something that looks like this. The smaller of the two numbers is the atomic number. which is also equal to the number of protons. The larger of the two numbers is known as the average atomic mass. Now sometimes you might see a problem that's written this way. They may tell you to find the number of protons, neutrons, and electrons for this particular element. Now in this format, The atomic number is on the bottom. The number on the top, notice that it's not the same as 22.99. In fact, it's rounded. This is not the average atomic mass, but rather it is the mass number. So this is a specific isotope of sodium. If you average all of the isotopes of sodium on Earth, you're going to get this number. So because that number is close to 23, this is the most abundant isotope of sodium on the earth. So in addition to sodium 23, you also have sodium 24 and there's also sodium 22. But as we said before, because the average atomic mass was 22.99, this is the most abundant isotope. which is also the most stable one on the Earth. The other forms of sodium, they're not stable and they're not very common, but these are other isotopes of sodium. Now, what you need to know is that the atomic number is associated with the identity of the element. So, sodium always has an atomic number of 11. Now, the mass number can change, and it will change for different isotopes. So, that number can vary. But the identity of the element is dependent on the atomic number. Now let's talk about the formulas that we need in order to calculate the number of protons, neutrons, and electrons. So let's start with the number of protons. This is always equal to the atomic number. That's it. So sodium always has 11 protons. Now the number of neutrons is the difference... between the mass number and the atomic number. And then the number of electrons is equal to the atomic number minus the charge of the species. So for an atom, let's say like aluminum, which doesn't have a charge, the charge is zero. The electrons will thus be equal to the atomic number. So for an atom, the number of electrons and protons are the same because the atom is neutral. But if we have an ion, let's say a positively charged cation, then the number of electrons will change. In this case, there's going to be three more protons than electrons. Or if we have an anion, like the phosphide anion. there's going to be three more electrons than protons. So for ions, the number of electrons and protons are different, but for atoms, which are electrically neutral, the number of protons and electrons are the same. So let's start with this example. Go ahead and calculate the number of protons, electrons, and neutrons for this element. So the number of protons is equal to the atomic number, which is the smaller of the two values, so that's going to be 11. The number of neutrons is the difference between the mass number, which is 23, and the atomic number, which is 11. So it's 23 minus 11, and that gives us 12. So we have 11 protons, 12 neutrons. Now for the number of electrons, it's equal to the atomic number, which is 11, minus the charge. Now there's no charge For this particular element, it's an atom, not an ion, so the charge is zero. So we have 11 electrons. So as we can see, for electrically neutral atoms, the number of protons and electrons are the same. Now let's consider another example. Aluminum 27 with a 3 plus charge. So here we have an ion. Go ahead and calculate the number of protons, neutrons, and electrons in this ion. So we can see that the atomic number is 13 and the mass number is 27. So the number of protons is always equal to the atomic number, which is 13 in this example. Now the number of neutrons is the difference between the mass number and atomic number. So it's 27 minus 13 which gives us 14. Now for the number of electrons, it's going to be the atomic number, which is 13, minus the charge on the ion, which is positive 3. So 13 minus 3 is 10. So for positively charged cations, there's going to be more protons than electrons. So because it has a positive 3 charge, there's 3 more protons than electrons. Now let's try a negatively charged anion. So this is the sulfide ion and let's calculate the number of protons, neutrons, and electrons. So we have an atomic number of 16 and a mass number of 33. So the number of protons, just like before, is equal to the atomic number, so that's 16. The number of neutrons is the difference between the mass number and atomic number, so 33 minus 16, so we have 17 for this example. And finally, the number of electrons is the atomic number, which is 16, minus the charge, which is negative 2. So 16 minus negative 2 is the same as 16 plus 2. So we get 18 electrons. Thus, for negatively charged ions or anions, you're going to have more electrons than protons. For an ion with a negative 2 charge, there's 2 more electrons than protons. Now, let's try a different example, or at least one that's presented in a different way. Find the number of protons. neutrons and electrons in silicon 29. So in this example we need to write this in a format that we're familiar with. So silicon 29 that tells us that the mass number is 29. But what about the atomic number? Well we need to use the periodic table. So if you go to it, if you don't have one you can go to google images, you'll find that silicon is the 14th element in the table. So it has an atomic number of 14. Now, there was no charge indicated in this problem, so we're going to assume that we're dealing with an atom and not an ion. Thus, we have 14 protons, because that's the atomic number, and the number of neutrons is going to be the mass number. minus the atomic number, so that's 29 minus 14, which gives us 15. Finally, the number of electrons is going to be the atomic number minus the charge, so it's 14. So for all atoms, the number of protons and electrons are the same. Now let's work on a challenge problem. So let's see if you truly understand the lesson in this video. So we have a cation with a 4 plus charge and it has 26 neutrons and 18 electrons. What is the identity of the element? Feel free to pause the video if you want to try it. By the way, for those of you who haven't done so already, feel free to subscribe to this channel and don't forget to click on that notification bell. Now let's begin working on this problem. So right now we're going to say that the unknown element is element X. So we know it has a 4 plus charge, and the number of neutrons is 26, the number of electrons is 18. In order to determine the identity of the element, what do we need to know? Remember, the atomic number identifies the element. So if we can determine the number of protons, we can... identify the unknown element. And so that's what we need to do in this example. Now, which of the three formulas that we wrote in the beginning can help us here? Is it this one? The number of protons is equal to the atomic number. Now, this is not going to help us because we know neither of these. Could we use this? The number of neutrons is equal to the mass number minus the atomic number. Now we have the number of neutrons, but we don't know the mass number or the atomic number. So the formula that is going to be helpful is the third one. The number of electrons is equal to the atomic number minus the charge. Because we know the charge and the number of electrons. With that, we can calculate the atomic number. So there's 18 electrons. I'm just going to write A for atomic number, and the charge is positive 4. So this becomes A minus 4. So we need to add 4 to both sides, and so the atomic number is 22. And the number of protons is equal to the atomic number, which is 22. Now, if we wish to calculate the mass number, we can. The number of neutrons was the difference between the mass number and the atomic number. If you rearrange that equation, you'll find that the mass number is the neutrons plus the atomic number. Or you could say it's the neutrons plus the protons, because the protons is the same as the atomic number. So it's 26 plus 22, which is 48. Now granted, that last step... wasn't really necessary, but I decided to do it anyway for those of you who were curious on how to get it. But let's focus on this number. So if you go to the periodic table and look for element 22, let me get mine real quick, you'll find that this corresponds to titanium. So this is the titanium 4 plus ion, and this is the answer. So titanium is the unknown element. And that's how you can identify any unknown element for these types of problems. Once you identify the number of protons, you can use a periodic table to identify the missing element.

The smaller of the two numbers is the atomic number. which is also equal to the number of protons. The larger of the two numbers is known as the average atomic mass.

Now sometimes you might see a problem that's written this way. They may tell you to find the number of protons, neutrons, and electrons for this particular element. Now in this format, The atomic number is on the bottom. The number on the top, notice that it's not the same as 22.99. In fact, it's rounded.

This is not the average atomic mass, but rather it is the mass number. So this is a specific isotope of sodium. If you average all of the isotopes of sodium on Earth, you're going to get this number. So because that number is close to 23, this is the most abundant isotope of sodium on the earth. So in addition to sodium 23, you also have sodium 24 and there's also sodium 22. But as we said before, because the average atomic mass was 22.99, this is the most abundant isotope.

which is also the most stable one on the Earth. The other forms of sodium, they're not stable and they're not very common, but these are other isotopes of sodium. Now, what you need to know is that the atomic number is associated with the identity of the element.

So, sodium always has an atomic number of 11. Now, the mass number can change, and it will change for different isotopes. So, that number can vary. But the identity of the element is dependent on the atomic number. Now let's talk about the formulas that we need in order to calculate the number of protons, neutrons, and electrons. So let's start with the number of protons.

This is always equal to the atomic number. That's it. So sodium always has 11 protons. Now the number of neutrons is the difference...

between the mass number and the atomic number. And then the number of electrons is equal to the atomic number minus the charge of the species. So for an atom, let's say like aluminum, which doesn't have a charge, the charge is zero. The electrons will thus be equal to the atomic number.

So for an atom, the number of electrons and protons are the same because the atom is neutral. But if we have an ion, let's say a positively charged cation, then the number of electrons will change. In this case, there's going to be three more protons than electrons. Or if we have an anion, like the phosphide anion. there's going to be three more electrons than protons.

So for ions, the number of electrons and protons are different, but for atoms, which are electrically neutral, the number of protons and electrons are the same. So let's start with this example. Go ahead and calculate the number of protons, electrons, and neutrons for this element. So the number of protons is equal to the atomic number, which is the smaller of the two values, so that's going to be 11. The number of neutrons is the difference between the mass number, which is 23, and the atomic number, which is 11. So it's 23 minus 11, and that gives us 12. So we have 11 protons, 12 neutrons.

Now for the number of electrons, it's equal to the atomic number, which is 11, minus the charge. Now there's no charge For this particular element, it's an atom, not an ion, so the charge is zero. So we have 11 electrons.

So as we can see, for electrically neutral atoms, the number of protons and electrons are the same. Now let's consider another example. Aluminum 27 with a 3 plus charge. So here we have an ion. Go ahead and calculate the number of protons, neutrons, and electrons in this ion.

So we can see that the atomic number is 13 and the mass number is 27. So the number of protons is always equal to the atomic number, which is 13 in this example. Now the number of neutrons is the difference between the mass number and atomic number. So it's 27 minus 13 which gives us 14. Now for the number of electrons, it's going to be the atomic number, which is 13, minus the charge on the ion, which is positive 3. So 13 minus 3 is 10. So for positively charged cations, there's going to be more protons than electrons. So because it has a positive 3 charge, there's 3 more protons than electrons.

Now let's try a negatively charged anion. So this is the sulfide ion and let's calculate the number of protons, neutrons, and electrons. So we have an atomic number of 16 and a mass number of 33. So the number of protons, just like before, is equal to the atomic number, so that's 16. The number of neutrons is the difference between the mass number and atomic number, so 33 minus 16, so we have 17 for this example. And finally, the number of electrons is the atomic number, which is 16, minus the charge, which is negative 2. So 16 minus negative 2 is the same as 16 plus 2. So we get 18 electrons. Thus, for negatively charged ions or anions, you're going to have more electrons than protons.

For an ion with a negative 2 charge, there's 2 more electrons than protons. Now, let's try a different example, or at least one that's presented in a different way. Find the number of protons.

neutrons and electrons in silicon 29. So in this example we need to write this in a format that we're familiar with. So silicon 29 that tells us that the mass number is 29. But what about the atomic number? Well we need to use the periodic table. So if you go to it, if you don't have one you can go to google images, you'll find that silicon is the 14th element in the table. So it has an atomic number of 14. Now, there was no charge indicated in this problem, so we're going to assume that we're dealing with an atom and not an ion.

Thus, we have 14 protons, because that's the atomic number, and the number of neutrons is going to be the mass number. minus the atomic number, so that's 29 minus 14, which gives us 15. Finally, the number of electrons is going to be the atomic number minus the charge, so it's 14. So for all atoms, the number of protons and electrons are the same. Now let's work on a challenge problem. So let's see if you truly understand the lesson in this video.

So we have a cation with a 4 plus charge and it has 26 neutrons and 18 electrons. What is the identity of the element? Feel free to pause the video if you want to try it. By the way, for those of you who haven't done so already, feel free to subscribe to this channel and don't forget to click on that notification bell.

Now let's begin working on this problem. So right now we're going to say that the unknown element is element X. So we know it has a 4 plus charge, and the number of neutrons is 26, the number of electrons is 18. In order to determine the identity of the element, what do we need to know?

Remember, the atomic number identifies the element. So if we can determine the number of protons, we can... identify the unknown element. And so that's what we need to do in this example.

Now, which of the three formulas that we wrote in the beginning can help us here? Is it this one? The number of protons is equal to the atomic number. Now, this is not going to help us because we know neither of these. Could we use this?

The number of neutrons is equal to the mass number minus the atomic number. Now we have the number of neutrons, but we don't know the mass number or the atomic number. So the formula that is going to be helpful is the third one.

The number of electrons is equal to the atomic number minus the charge. Because we know the charge and the number of electrons. With that, we can calculate the atomic number.

So there's 18 electrons. I'm just going to write A for atomic number, and the charge is positive 4. So this becomes A minus 4. So we need to add 4 to both sides, and so the atomic number is 22. And the number of protons is equal to the atomic number, which is 22. Now, if we wish to calculate the mass number, we can. The number of neutrons was the difference between the mass number and the atomic number.

If you rearrange that equation, you'll find that the mass number is the neutrons plus the atomic number. Or you could say it's the neutrons plus the protons, because the protons is the same as the atomic number. So it's 26 plus 22, which is 48. Now granted, that last step... wasn't really necessary, but I decided to do it anyway for those of you who were curious on how to get it.

But let's focus on this number. So if you go to the periodic table and look for element 22, let me get mine real quick, you'll find that this corresponds to titanium. So this is the titanium 4 plus ion, and this is the answer. So titanium is the unknown element.

And that's how you can identify any unknown element for these types of problems. Once you identify the number of protons, you can use a periodic table to identify the missing element.

Transcript for:Understanding Atoms and Ions: Protons, Neutrons, Electrons

Transcript for:
Understanding Atoms and Ions: Protons, Neutrons, Electrons