Welcome, my dear students, to our Chapter 2, Part 1 video lecture from our two-semester General Chemistry series. After today's lecture, you should be able to define the following terms from the periodic table. Define neutrons, protons, and electrons.
Write chemical symbols for elements, including isotopes. Calculate elements'atomic weights from their relative isotopic abundances. And define empirical versus molecular formulas. Are you ready? Let's begin.
But before we get started, I wanted to share with you a humorous chemistry cat of the day from QuickMeme.com. Tell a potassium joke? Okay. Alright.
Let's continue. Today I'll be teaching you more about elements and the periodic table. Did you know, for example, that there are over 114 elements known?
83 are stable and found in nature, though many of these are very rare. 7 are found in nature, but are radioactive, and 24 or more are not naturally found on Earth. Two or three of these might be found in stars.
Now, elements can be organized according to their properties on a magical chart called the periodic table, which is found in the back of our... class textbook. So here's what the periodic table looks like. Now in spite of being somewhat unassuming in appearance, this table contains a wealth of information critical for understanding everything about the physical world around us. And this information took humankind many centuries of research to discover.
Now one thing I want to clarify is this. If we zoom in on this section of the periodic table, you'll note that going from elements 56 to 57, suddenly the periodic table moves down to this block, located here. And then as we scroll across this row, we get to element number 70, and then number 71 goes back up over here. You'll see the same thing happens when we look at element 88. Moving to 89, we also go back down here. We then scroll across the row, get to element 102, and find that number 103 continues back over here.
What the heck? I mean, what's going on? Well, as it turns out, this block section of the periodic table...
actually belongs here. The problem is that if we include this block section right here, which is called the F block, and the periodic table like we see on this slide, it makes the table really wide and kind of hard to see on a regular sheet of paper. So that's why the F block is usually drawn below everything else, as seen here.
But you should remember that if we draw it out properly, the F block would actually appear as seen right here. even though it's typically drawn beneath the other blocks. You might ask then, well, why do we even separate the elements into blocks like this at all anyway? Why don't we just put them on the periodic table alphabetically or something?
The reason is that these elements are all sorted on the periodic table in a very specific way according to their individual chemical properties. These other blocks, by the way, are called the S, D, and P blocks. But that's not really important that right now. It will become very important during the later chapter.
I did want to point out that the first row of the F block is called the lanthanides, and the second row is called the actinides. As I mentioned before, the typical textbook periodic table looks kind of boring, but it doesn't have to be this way. If you'd like to see a more exciting version of the periodic table, I recommend going to this link right here at PeriodicTable.com, where we can see a really cool interactive periodic table.
that looks like this. As you can see, if you point at any one of the elements on this periodic table, it'll show you a photograph of what that element looks like in its natural state, and it will show some information about that element's history. Now for some neat periodic table vocabulary.
As we look across the periodic table, it's important for you to remember that each column in the periodic table is called a group. Atoms that are in the same group or column as each other have similar properties. Similarly, each row in the periodic table is called a period.
Now to something else. You'll notice that each element on the periodic table is assigned a number called an atomic number, which corresponds to which box it appears in on the table. Hydrogen's atomic number is 1, for example.
Helium's is 2, lithium's is 3, and so forth. You'll also frequently see that in each element's box there's another number called the element's atomic mass. That's it. Hydrogens is 1.00794.
Heliums is 4.0026. Lithiums is 6.941, and so on. What in the world are these two sets of numbers, and what do they mean? Well, don't worry, I'll tell you. Though that will have to wait for a little bit later.
This brings us to our first lecture-based question. Based on what we've seen in the previous slide, Which pair of elements would you expect to exhibit the greatest similarity in their physical and chemical properties? We'll now continue. Each group or column on the periodic table has a different name.
Now that being said, there are four specific group names that I require you, my students, to memorize. These names are the alkali metals, which are the elements in column or group 1A, the alkaline earth metals, which are found in column or group 2A, The halogens, which are column or group 7A, and the noble gases, which are column 8A. This brings us to our next chapter problem. The elements in groups 1A, 6A, and 7A are called what, respectively?
Now, although I didn't tell you the name of the elements in column 6A, I'm betting that you can look it up. As I mentioned earlier, the periodic table is structured so that the elements are organized according to their chemical properties. One thing that is essential to remember is this.
Elements found on the right side of the periodic table are called non-metals. They're shown in blue colored here. And they have very specific and similar chemical properties to each other. The majority of elements found in this large gray section over here are called metals.
And they also have similar properties to each other. The elements who straddle the line between nonmetals and metals are called metalloids. They're highlighted in yellow here. Metalloids have some of the properties that metals have and some of the properties that nonmetals have.
Hence, they kind of straddle the intermediary line between the two different families of elements. I now wish to teach you more about atoms. Atoms are tiny, about 10 to the negative tenth meters in diameter. Atoms are tiny, about 10 to the negative tenth meters in diameter. In fact, they are so tiny that if all of the atoms in your body were increased in size to be just one inch in diameter, you'd bump your head on the moon.
As it turns out, there are a huge number of atoms in even a small sample of an element. For example, a one-half carat diamond, which is made up primarily of nothing but zillions and zillions of carbon atoms, has five times ten to the twenty-first atoms in it. Now if these atoms were all lined up in a single file line, even at their regular atomic size, that line would be so long that it would stretch all the way from the Earth to the Sun.
And believe it or not, there are actually even smaller particles located inside atoms. I'm going to teach you about three of them, with which you will shortly become familiar. The first is the neutron.
Neutrons are located inside atoms nuclei, or the atoms nucleus. Neutrons have no charge, and their mass is around 1.00867 amu. Now, just so you guys know, an amu is an abbreviation for an atomic mass unit, which is equal to 1 twelfth the mass of a carbon atom.
The second subatomic particle I will teach you is protons. Protons are also located inside atoms'nuclei. They have a plus one charge, and their mass is about the same as that of neutrons, 1.00728 amu.
The last subatomic particle I will teach you is electrons. They're located in a type of orbit around the atom's nuclei. Their charge is negative 1, and their mass is very, very, very small.
For simple mathematical purposes, we often discount the mass of electrons as if their masses were actually zero.