Lecture, Wednesday, August 21, 2002

We covered lots of definitions (see lecture outline for Wednesday, August 21, 2002) in class. We discussed the elements in the periodic table, their symbols, their formulas and their standard state or phase. Standard state means the phase of the element at 25 degrees Celsius and 1 atmosphere of pressure (atmosphere pressure). You have to know the spelling of the the first twenty elements and 20 common elements. The common elements I mentioned, so far, in class were; Fe, Cu, Br, Rb, Mo, Ag, Sn, I, Cs, Ba Au, Hg, Pb and U. There are some more that I will mention in class. So you have to be able to spell the names of these elements, and know the formula of each (that we would use in a chemical equation).

Symbols and formulas for the elements can be the same, and are for most substances, but that is not always the case. You need to know those elements with a formula that is different than their symbol. The elements with formulas that differ from their elements were; hydrogen, nitrogen, oxygen, fluorine, phosphorus, sulfur, chlorine, bromine and iodine.

You also have to know the standard state phase of ALL elements in the periodic table. This is not too big a job to learn. Memorize the elements that are gases and liquids, then everyone else is a solid.

We view several reactions (see Lecture Graphics for Wednesday, August 21, 2002). You will need to know these reactions for our first exam. What do I mean by 'know these reactions'?

You will have to be able to describe what happened in the reaction, and you will need to write a balanced chemical equation which describes what happens in a symbolic way. For example, we observed the reaction between iron and sulfur.

Description:

Dark/black iron powder was mixed with yellow sulfur powder. The two elements did not react upon mixing. This was apparent because a magnet was used to separate the iron from the sulfur after the two elements were mixed. When the iron and sulfur were mixed they formed a heterogeneous mixture. One could see lumps of sulfur in the mixture. Some of the mixture was added to a test tube and the test tube was heated. In the test tube you could see some change. The mixture darkened, and you could see some bubbling, caused by the melting sulfur. The test tube was heated red hot. After the sample had cooled the mixture was removed and it appeared to look different that the initial mixture. It was a solid mass, instead of a powdered mixture. The color was different. When a magnet was brought close to the material, no elemental iron appeared on the poles of the magnet. A new compound had been formed.

The chemical equation that symbollically represents this reaction is,

Fe(s) + S₈(s) ---> FeS(s)

8Fe(s) + S₈(s) ---> 8FeS(s)

Another form of iron was also probably formed in this reaction,

12Fe(s) + S₈(s) ---> 4Fe₃S₂(s)

But the first reaction is enough for our purposes.

We observed several other reactions in class. You should be able to write a brief description and write a balanced chemical equation for those reactions also.

We also looked at some video showing examples of homogeneous and heterogeneous mixtures. These are also located at the Lecture Graphics link.

I mentioned, only briefly, the term physical properties, but we spent the lecture discussing physical properties of several elements and compounds. The lecture notes for Wednesday's class and our textbook discuss physical properties in more details. I'll expect you to review that material so you can do Problem Set 1.1 and PS1.2. If you have questions, e-mail me or drop by my office hours.

A student came up after class and asked about chemical properties. How to tell the chemical properties for a substance. Chemical properties have to do with whether a substance reacts with another substance or not. For example, iron metal reacts with sulfur. So each of those elements has a chemical property relative to their reaction with the other. So a chemical property of iron would be its ability to react with sulfur when heated. Sulfur has the chemical property of reacting with iron when heated.

Now here it gets interesting. We can use our intuition to extend some of the chemical properties of both of these elements. The element oxygen is above iron in the periodic table. Therefore, we might guess that iron would react with oxygen. to form a similar compound (FeO or Fe₃O₂). And that does happen. Similarly if sulfur reacts with iron, we might guess that is would react with other metals also. That in fact happens, although we will need more experience to predict what the formulas of the compounds would be when sulfur combined with other metals.

Are you suppose to know all the physical and chemical properties of every element and compound. Let me assure you the answer is NO! But I will expect you to know those properties of substances discussed/covered in class, problem sets and laboratory. But even for those substances I would not expect you to know the boiling point or melting point...that sort of specific detail (although you'd better know that for water), but color and phase, relative density are important.

To help you find physical properties and chemical properties of the elemetns there s a very nice Periodic Table maintained by Mark Winter. The information at this site will help you on PS1.

After Wednesday's class you should be able to do PS1.1, PS1.2 and most if not all of PS1.3. remember in PS1.3 that you must provide a reason.

We did not get to the discussion on Atomic Theory and Microscopic Model of Matter. However, we are covering that in the ICE#1 in laboratory this week. Also BLB show similar pictures depicting the microscopic model of matter in Section 1.2. Check out the lecture notes on Atomic Theory. There are some links that will be useful. You may also find the additional notes link useful that is at the bottom of the Lecture notes for Wednesday.

So our first lecture down. As you can see I did not cover everything in the lecture notes in class on Wednesday. That is likely to continue to happen. I will still hold you responsible for the material in the lecture notes. If you have questions over content covered in the lecture notes that I did not (or thought I'd not) cover during lecture you are welcome to drop by and visit me or send an e-mail. Sometime I will discuss the missed material in the next lecture, sometimes I'll simply tell you to review the material in the notes and the textbook and see me if you have questions.