Nuclear Symbols and Isotopes Explained

So now that we've talked about ions and we've talked about isotopes and we've defined the atomic mass and we've defined the atomic number, we're going to take a look at how chemists symbolize this or shorthand it. And so we use nuclear symbols, as we already said, the atomic number, the z-numbers, the number of protons in the nucleus. The mass number or the A number is the number of protons plus the number of neutrons or the Z number plus the number of neutrons if you want to get technical. Okay remember isotopes are the atoms of the same element which means atoms with the same Z number but with different numbers of neutrons in their nuclei. And we can symbolize this by putting the A number over the Z number and X is the element symbol from off the periodic table. And we've got a couple examples at the bottom that will go into more detail when we take a look at nuclear because if you'll notice we've got a hydrogen with a mass of one, hydrogen with a mass of two, and hydrogen with a mass of three. The D and the T represent actually deuterium and tritium. Actually, the isotopes of hydrogen with a mass of two and the hydrogen with a mass of three are the only two isotopes on the whole periodic table that chemists actually give a separate name to. We're going to find out how we name them. Basically, we're just going to take the elemental name, put a dash in the mass number. So we have uranium-235 and uranium-238. The uranium-238 is not really that much of a problem. The uranium-235 is what's used in nuclear power plants and atomic bombs. Again, we'll take a look at that as the last topic at the end of this course. So what you may want to do is take a second. in your slot notes and make a note that the mass number goes on the upper left and the atomic number goes on the lower left of our symbol. And then the charge is on the upper right. Remember I talked about with Benjamin Franklin rubbing the glass rod and getting a negative charge. So the problem is, is we're not used to gaining and losing negative numbers. You didn't even learn about negative numbers until later on in your academic career. So I find that to kind of keep this straight, because sometimes if you try and just do it in your head, you can get it backwards, that the charge is always equal to the number of protons minus the number of electrons. The interesting thing about this formula is I can swap any of those two and come up with the answer. So if I wanted the electrons, I would take the number of protons minus the charge. If I wanted the protons, I would take the charge minus the number of electrons and it would give me the protons. So this is a real simple equation, and it kind of helps us keep that straight. So let's take a look at a couple examples. So it says determine the number of protons, neutrons, and electrons. And so I've given you the symbol. And so by default or definition, the atomic number or the mass, sorry, the mass number is going to be 16 because it's always on the top. The atomic number is going to be on the bottom, so it's going to be 8, and this is international convention. In all chemistry classes it's this way. So we now know the atomic number is equal to the number of protons. If we know the atomic number plus the number of neutrons equals the mass number, we can do the mass number minus the atomic number. The big number minus the small number gives us eight. It's not always going to be half. And because there is no charge, this is a neutral atom. And so the protons is going to be equal to the number of protons. It's not always going to be equal to the number of protons. And very seldom is it equal to the number of protons. So more typically you're going to get oxygen with a 2 minus or a minus 2 charge. Notice the difference between the two. So if you'll notice the mass number stays the same and the atomic number stays the same because it's the same element. Okay this is an ion. It's an anion because it's got a negative charge. So the protons stay the same. The neutrons stay the same. What difference is the number of electrons? And so what we find is protons minus the charge gives us the number of electrons. So 8 minus, again, we've got to be careful because those electrons are negatively charged. So 8 minus a negative 2 is 10. not six. So we've got to be real careful. All because Benjamin Franklin said the electrons had a negative charge. At least he didn't just call it blue or red. Then we'd really have a whole lot of fun trying to figure this out. So let's change it up one more time. And we're going to do a different element. So notice we've got a different mass number. and we have a different atomic number. Our protons is now equal to 56. We've got a new atomic number. Our neutrons mass number minus atomic number 137 minus 56. Notice that's greater than half. And if you'll notice this is a cation because it's positively charged. So if we do 56 minus a positive 2, we end up with 54 as the number of electrons. So let's take a look at a couple of questions. Okay. Number 10, in what ways are isotopes of a given element always different? In what ways are they the same? Well, they're different in their mass numbers because they got... different numbers of neutrons but they always have the same atomic number because it's the number of protons that gives an atom its identity it's the number of protons that define what type of atom that you're looking at so number 11 it says write the symbol for each of the following ions and I only picked 11a okay so we want an ion with a 1 plus charge and atomic number 55 and a mass number of 133 well let's see the atomic number gives us the identity so I'm gonna pick on 55 because that's gonna tell us which atom on the periodic table and so you go to your periodic table and you find atomic number 55 and what you're gonna find is it's cesium The mass number is 133, so that goes on above the 55, and it's got a one plus charge. Now sometimes you'll see this written as plus one instead of one plus, and that's fine. It all depends on how you're defining that number and what's happening. So if you write it as plus one or one plus, both of those are absolutely right as far as we're concerned in our class. Number 16, determine the number of protons, neutrons, and electrons in the following isotopes that are used in medical diagnoses. So atomic number 9, protons, it's the atomic number 9. If we look on the periodic table, it's fluorine because it's going to ask us to name the element. And the number of neutrons, the mass number minus the atomic number gives us 9. This one happens to be half. and the electrons protons again notice that nine minus a negative one is ten electrons and fluorine is used in what's called a fluoroscope um which is used in medical diagnoses that causes things to glow so they're easier to see on x-rays In number 17, let's see, we have an atomic number of 26 mass. Oh, we need the atomic number to tell us that it's iron and give us the number protons. Neutrons, mass number minus the atomic number, 58 minus 26. Notice that's greater than half. and the electrons protons minus the charge so we've got atomic number of 26 minus and it gives us a plus 2 or 2 plus charge so we end up with 24 electrons number 18 it gives us the symbol and it wants the number of protons. So the protons is equal to the atomic number. The neutrons, 10 minus 5 is 5. And because there is no charge on this, the protons is equal to the number of electrons. At this point, we've talked about the atomic masses, which is the number of protons plus the number of neutrons. But if you'll notice, your periodic table doesn't have whole numbers for atomic masses. There's actually some decimals, like helium is 4.003 and carbon is 12.01. So what we find is because we have those isotopes, we... don't have an even amount of them so we need to take what's called a weighted average and how we find that is we use what's called a mass spectrometer um and basically what they do is they ionize the atoms and then they accelerate them and then they measure how fast they can turn on the right hand side is what's called a hap site it's what i used when i was in the navy um but not and that use can actually determine the identity of molecules by their masses by breaking them apart in different pieces and how fast they'll actually come out of a column. But the point behind this is we now have the technology where we can measure the individual masses of atoms. And so our atomic masses are actually weighted averages. So in order to... find that weighted average or that decimal, we need to know both the masses of the isotopes and their abundance in nature. And we call that mass spectrometry. And the two pieces of equipment I showed you on the previous slide can help us do that. So this is one of our areas where we can basically look at something in the macroscopic world and understand the microscopic world. So. what we find is the atomic mass is the mass of an atom and atomic mass units. And by definition, an atomic mass unit is 1 12th of a carbon 12 atom. So if we use the mass spectrometer in order to figure this out, what we find is hydrogen has a mass of 1.2 or hydrogen 1 has a mass of 1.008. And oxygen-16 has an atomic mass of 16.00. So what we find is the numbers that we have on the periodic table, notice our carbon is 12.01, is an average atomic mass or actually a weighted. So if you'll notice the carbon that's in your body is about 98.90% carbon-12 and 1. point one zero percent carbon 13 so if we were to take the weighted average of all the carbon in your body we'd end up with an atomic mass of about twelve point oh one so let's take a look at lithium the nice about lithium it's only got two isotopes so it makes it relatively simple to kind of get an idea of the concept of this okay so if we take a look at lithium we got lithium 6 and lithium 7 And if we use a mass spectrometer, what we find is lithium-6 is specifically 6.015, and lithium-7 is specifically 7.016. Both of those out to four significant figures. And then we can figure out the percent or the abundance, 7.42 and 92.58. So we just can't take the atomic masses, the 6.015 and the 7.016, add them together and divide by two. we need to do what's called a weighted average. Well there's a formula for that and that can get kind of intimidating. But ultimately what we find is if we take each mass times its percent over 100 and add them the two together we end up with 6.941 instead of about 6.5 if we were just to average the two together. And what we find is on your periodic table that's in your references, if you take a look at lithium, it's got a mass of 6.94. OK, your periodic table basically takes everything out to four significant figures. And that makes our numbers a little bit easier to deal with when we go to do some of our calculations. So let's take a look at an atom that has three different isotopes. And if you'll notice, we just take the mass, the 19.99 amu times 90.92 over 100, and we do the 20.99, and we do the 21.99 times this percent, we get 20.169. And if you look on the periodic table, that's pretty most likely the element is neon. So this can actually be used as an intrinsic property to identify the atom. And a couple slides back, that piece of equipment that I showed you that had the computer next to it, that's what it does is it actually will try to figure out what the elements or more specifically what the compounds are. It was one of the pieces of equipment that I used when I was in my last reserve unit in the Navy that we would use it to collect samples and identify what molecules were present in either the water, soil, or air. the limitations is is the molecules had to be small enough so you could vaporize them and so this engine ends sections 2.3

Okay remember isotopes are the atoms of the same element which means atoms with the same Z number but with different numbers of neutrons in their nuclei. And we can symbolize this by putting the A number over the Z number and X is the element symbol from off the periodic table. And we've got a couple examples at the bottom that will go into more detail when we take a look at nuclear because if you'll notice we've got a hydrogen with a mass of one, hydrogen with a mass of two, and hydrogen with a mass of three.

The D and the T represent actually deuterium and tritium. Actually, the isotopes of hydrogen with a mass of two and the hydrogen with a mass of three are the only two isotopes on the whole periodic table that chemists actually give a separate name to. We're going to find out how we name them. Basically, we're just going to take the elemental name, put a dash in the mass number.

So we have uranium-235 and uranium-238. The uranium-238 is not really that much of a problem. The uranium-235 is what's used in nuclear power plants and atomic bombs.

Again, we'll take a look at that as the last topic at the end of this course. So what you may want to do is take a second. in your slot notes and make a note that the mass number goes on the upper left and the atomic number goes on the lower left of our symbol.

And then the charge is on the upper right. Remember I talked about with Benjamin Franklin rubbing the glass rod and getting a negative charge. So the problem is, is we're not used to gaining and losing negative numbers. You didn't even learn about negative numbers until later on in your academic career.

So I find that to kind of keep this straight, because sometimes if you try and just do it in your head, you can get it backwards, that the charge is always equal to the number of protons minus the number of electrons. The interesting thing about this formula is I can swap any of those two and come up with the answer. So if I wanted the electrons, I would take the number of protons minus the charge.

If I wanted the protons, I would take the charge minus the number of electrons and it would give me the protons. So this is a real simple equation, and it kind of helps us keep that straight. So let's take a look at a couple examples. So it says determine the number of protons, neutrons, and electrons. And so I've given you the symbol.

And so by default or definition, the atomic number or the mass, sorry, the mass number is going to be 16 because it's always on the top. The atomic number is going to be on the bottom, so it's going to be 8, and this is international convention. In all chemistry classes it's this way.

So we now know the atomic number is equal to the number of protons. If we know the atomic number plus the number of neutrons equals the mass number, we can do the mass number minus the atomic number. The big number minus the small number gives us eight. It's not always going to be half.

And because there is no charge, this is a neutral atom. And so the protons is going to be equal to the number of protons. It's not always going to be equal to the number of protons.

And very seldom is it equal to the number of protons. So more typically you're going to get oxygen with a 2 minus or a minus 2 charge. Notice the difference between the two.

So if you'll notice the mass number stays the same and the atomic number stays the same because it's the same element. Okay this is an ion. It's an anion because it's got a negative charge.

So the protons stay the same. The neutrons stay the same. What difference is the number of electrons?

And so what we find is protons minus the charge gives us the number of electrons. So 8 minus, again, we've got to be careful because those electrons are negatively charged. So 8 minus a negative 2 is 10. not six.

So we've got to be real careful. All because Benjamin Franklin said the electrons had a negative charge. At least he didn't just call it blue or red.

Then we'd really have a whole lot of fun trying to figure this out. So let's change it up one more time. And we're going to do a different element.

So notice we've got a different mass number. and we have a different atomic number. Our protons is now equal to 56. We've got a new atomic number. Our neutrons mass number minus atomic number 137 minus 56. Notice that's greater than half. And if you'll notice this is a cation because it's positively charged.

So if we do 56 minus a positive 2, we end up with 54 as the number of electrons. So let's take a look at a couple of questions. Okay.

Number 10, in what ways are isotopes of a given element always different? In what ways are they the same? Well, they're different in their mass numbers because they got... different numbers of neutrons but they always have the same atomic number because it's the number of protons that gives an atom its identity it's the number of protons that define what type of atom that you're looking at so number 11 it says write the symbol for each of the following ions and I only picked 11a okay so we want an ion with a 1 plus charge and atomic number 55 and a mass number of 133 well let's see the atomic number gives us the identity so I'm gonna pick on 55 because that's gonna tell us which atom on the periodic table and so you go to your periodic table and you find atomic number 55 and what you're gonna find is it's cesium The mass number is 133, so that goes on above the 55, and it's got a one plus charge. Now sometimes you'll see this written as plus one instead of one plus, and that's fine.

It all depends on how you're defining that number and what's happening. So if you write it as plus one or one plus, both of those are absolutely right as far as we're concerned in our class. Number 16, determine the number of protons, neutrons, and electrons in the following isotopes that are used in medical diagnoses. So atomic number 9, protons, it's the atomic number 9. If we look on the periodic table, it's fluorine because it's going to ask us to name the element.

And the number of neutrons, the mass number minus the atomic number gives us 9. This one happens to be half. and the electrons protons again notice that nine minus a negative one is ten electrons and fluorine is used in what's called a fluoroscope um which is used in medical diagnoses that causes things to glow so they're easier to see on x-rays In number 17, let's see, we have an atomic number of 26 mass. Oh, we need the atomic number to tell us that it's iron and give us the number protons.

Neutrons, mass number minus the atomic number, 58 minus 26. Notice that's greater than half. and the electrons protons minus the charge so we've got atomic number of 26 minus and it gives us a plus 2 or 2 plus charge so we end up with 24 electrons number 18 it gives us the symbol and it wants the number of protons. So the protons is equal to the atomic number. The neutrons, 10 minus 5 is 5. And because there is no charge on this, the protons is equal to the number of electrons.

At this point, we've talked about the atomic masses, which is the number of protons plus the number of neutrons. But if you'll notice, your periodic table doesn't have whole numbers for atomic masses. There's actually some decimals, like helium is 4.003 and carbon is 12.01. So what we find is because we have those isotopes, we... don't have an even amount of them so we need to take what's called a weighted average and how we find that is we use what's called a mass spectrometer um and basically what they do is they ionize the atoms and then they accelerate them and then they measure how fast they can turn on the right hand side is what's called a hap site it's what i used when i was in the navy um but not and that use can actually determine the identity of molecules by their masses by breaking them apart in different pieces and how fast they'll actually come out of a column.

But the point behind this is we now have the technology where we can measure the individual masses of atoms. And so our atomic masses are actually weighted averages. So in order to...

find that weighted average or that decimal, we need to know both the masses of the isotopes and their abundance in nature. And we call that mass spectrometry. And the two pieces of equipment I showed you on the previous slide can help us do that. So this is one of our areas where we can basically look at something in the macroscopic world and understand the microscopic world. So.

what we find is the atomic mass is the mass of an atom and atomic mass units. And by definition, an atomic mass unit is 1 12th of a carbon 12 atom. So if we use the mass spectrometer in order to figure this out, what we find is hydrogen has a mass of 1.2 or hydrogen 1 has a mass of 1.008. And oxygen-16 has an atomic mass of 16.00.

So what we find is the numbers that we have on the periodic table, notice our carbon is 12.01, is an average atomic mass or actually a weighted. So if you'll notice the carbon that's in your body is about 98.90% carbon-12 and 1. point one zero percent carbon 13 so if we were to take the weighted average of all the carbon in your body we'd end up with an atomic mass of about twelve point oh one so let's take a look at lithium the nice about lithium it's only got two isotopes so it makes it relatively simple to kind of get an idea of the concept of this okay so if we take a look at lithium we got lithium 6 and lithium 7 And if we use a mass spectrometer, what we find is lithium-6 is specifically 6.015, and lithium-7 is specifically 7.016. Both of those out to four significant figures.

And then we can figure out the percent or the abundance, 7.42 and 92.58. So we just can't take the atomic masses, the 6.015 and the 7.016, add them together and divide by two. we need to do what's called a weighted average.

Well there's a formula for that and that can get kind of intimidating. But ultimately what we find is if we take each mass times its percent over 100 and add them the two together we end up with 6.941 instead of about 6.5 if we were just to average the two together. And what we find is on your periodic table that's in your references, if you take a look at lithium, it's got a mass of 6.94.

OK, your periodic table basically takes everything out to four significant figures. And that makes our numbers a little bit easier to deal with when we go to do some of our calculations. So let's take a look at an atom that has three different isotopes.

And if you'll notice, we just take the mass, the 19.99 amu times 90.92 over 100, and we do the 20.99, and we do the 21.99 times this percent, we get 20.169. And if you look on the periodic table, that's pretty most likely the element is neon. So this can actually be used as an intrinsic property to identify the atom. And a couple slides back, that piece of equipment that I showed you that had the computer next to it, that's what it does is it actually will try to figure out what the elements or more specifically what the compounds are. It was one of the pieces of equipment that I used when I was in my last reserve unit in the Navy that we would use it to collect samples and identify what molecules were present in either the water, soil, or air.

the limitations is is the molecules had to be small enough so you could vaporize them and so this engine ends sections 2.3

Transcript for:Nuclear Symbols and Isotopes Explained

Transcript for:
Nuclear Symbols and Isotopes Explained