This video is on the atom and isotopes. Starting with elements and compounds. Elements consist of only one type of atom, and they cannot be broken down into anything smaller. So, for example, take any element on the periodic table.
Let's take oxygen. Oxygen is only composed of oxygen atoms. There is nothing else. You cannot split...
or break oxygen atoms down into anything else. An atom is the smallest unit of matter. A compound consists of more than one type of atom, and that can be broken down into its elements. So again, an element, let's take oxygen.
I have a 2 there because it's diatomic, it's special. A compound is more than one element. Let's take water, for example.
So I can break water apart into H and O. through electrolysis, but O is just O. Atoms have a very small, very dense, and very positive nucleus. That's one word that's not here, a positive nucleus.
The reason it is positive is because it contains protons and neutrons. Protons have a positive charge. Neutrons... have a neutral charge, they don't have any charge.
And then electrons, which is outside of the nucleus, have a negative charge. So an electron cloud is the region where the electrons are most likely to be found. And I will show you a picture in one of the next slides of what an atom would look like here. So if this is your atom, You have your very small nucleus consisting of protons and neutrons.
And then your electron cloud, notice how much bigger your electron cloud is than your nucleus. Your electrons are floating out here. Recall in a neutral atom, the number of protons equals the number of electrons.
So in this picture, looks like protons are the blue spheres. It looks like there are six protons. So there would be six electrons out here in a neutral atom. Most of the atom's mass comes from the protons and the neutrons.
So the electrons have a very small, negligible mass. Most of the volume of the atom comes from the electrons. And again, if you look back at the picture, we can see that the electrons take up a lot of room.
This whole cloud is from the electrons. And the charge is determined by the protons and the electrons. Again, protons positive, electrons negative.
Neutrons are neutral, so they don't play a part in the charge. If your protons equal your electrons, you have a neutral atom. If I have four pluses, and four minuses, they cancel.
On the periodic table, you will see many boxes, 118 of them. The number at the top is called your atomic number. That is the number of protons that an element has.
If you change the number of protons, you change the element altogether. In the middle, that would be your atomic symbol. This element AU is gold. And at the bottom is your atomic mass.
And that is the average mass of the atoms of an element. It takes all of what's called the naturally occurring isotopes, and it does a weighted average, which we will do those calculations. Our periodic table, a lot of times...
We'll round the atomic mass to two decimal places. So as you can see here, we have two decimal places. So for gold, notice the two spots there.
So, we're going to fill in the blanks with either protons, neutrons, or electrons. Blank and blank are located in the nucleus. is the protons and the neutrons. Again, that is why the nucleus is positively charged, because it has those positive protons, and it has the neutrons at no charge. Blank have a negligible mass, that is your electrons.
Most of the mass of the atom comes from the protons and the neutrons. We know that protons are positive, and electrons are negative. Calcium, atomic number 20, is a major constituent of bones and teeth.
How many protons and electrons are present in a neutral atom of calcium? Your atomic number tells you your protons. So that tells me that there are 20 protons.
Because it is neutral, I can say that there are also 20 electrons. What is the atomic number for each of these elements? You are just referring to the periodic table. So we're looking for phosphorus, sulfur, and chlorine. So phosphorus we can see is 15, sulfur is 16, and chlorine is 17. Again, they tell you the number of protons.
Isotopes. All atoms of an element contain the same number of protons and electrons. So if I have a sample of magnesium on the desk in front of me, all of the atoms comprised in that magnesium sample, they all have the same number of protons and electrons. Magnesium would be element number 12, so they would all have 12 protons and all have 12 electrons. However, They may contain different numbers of neutrons.
So what an isotope is, it's an atom with different numbers of neutrons. So you have carbon, for example. Carbon has three isotopes. Carbon-12, carbon-13, carbon-14. This is called hyphen notation, how it's written here.
There's two different notations, which we'll get to. Each isotope does something different. So carbon-14 dating, which you may have heard of, that is to age dinosaur fossils. In this specific case, this carbon happens to have eight neutrons and six protons. Carbon-13 isotope, I'm not sure what that does, but that has seven neutrons and six protons.
And carbon-12 would have six neutrons, six protons. Notice that in each case, the protons stay the same. Carbon always has six protons.
So how do we figure out these numbers? How do I figure out those numbers there? The mass number is the number of protons plus the number of neutrons. It's a very easy calculation.
So carbon, which we just talked about, 12, 13, and 14. If it has six protons and six neutrons, you just add them to get your mass number. Six and seven, six and eight. So this formula you need to know. Two different notations for isotopes.
You have the hyphen notation and the nuclear notation. So the hyphen notation, you have the element name. or the symbol, it does not matter, with a little dash, and then you have the mass number. So iodine-125 or just I-125.
That 125 is my mass number. I can get my atomic number of iodine from the periodic table. The nuclear symbol, slightly different, it has the mass number as a superscript. and it has the atomic number as a subscript, and then it has the element symbol. The nuclear symbol is a little bit nicer just because it gives you your atomic number, the 53. Up here, unless I had it memorized, I would have to look at the periodic table to tell me how many protons or what the atomic number was.
On the right here, you can see that I have hyphen notation. I'm going to write the nuclear notation to the left. So carbon 12, 12 is the mass number.
So I have my symbol with the mass number up top. The bottom is the atomic number. The atomic number of carbon is 6. Carbon 13, again, mass number. Atomic number would not change. It's still carbon and 14 with a 6 So depending on what you're given you can fill in accordingly So if I have my isotope barium 131 the number after the hyphen is my mass number The atomic number, I would look on my periodic table at barium.
I can do that for you. Barium is 56. That's my atomic number, which tells me my number of protons. And recall your little formula, mass number equals protons plus neutrons.
So to find the neutrons, I can just do my mass number minus my protons. So 131 minus 56 would give me 75. And working kind of backwards here, the second row, the atomic number is 80. So I know my protons are 80. My mass number is just my protons plus my neutrons. So 80 plus 117 is 197. And my isotope name, what element is it?
I look at my atomic number there. So element number 80 is mercury. I'm just going to use the symbol, dash, the mass number.