• Chemistry deals with the properties of materials and the changes these materials undergo. (DLB, 7th Ed., Prentice-Hall)

• Chemistry is a physical science that deals with the composition, structure and properties of substances and the reactions they undergo. As a science, chemistry involves the intuitive and creative application of knowledge gained from experiment observation and theoretical descriptions.

• Anything that bites or scratches is biology

  Anything that stinks or pops is chemistry

  Anything that does not work is physics

In the definitions about terms like...materials, substances are used. The term matter could replace both of these words. The two distinguishing characteristics of matter is that matter is classified as anything that has mass and occupies space. While it is possible to list examples of matter, we might also say pretty much everything meets the criteria for matter, except, for example, energy and light. So examples of matter would include, the chairs we sit on and the air we breath. However, the heat we feel from burning natural gas is not matter. The natural gas that is burning, and the oxygen that is reacting with the natural gas are both examples of matter. But the heat, or light produced in the reaction is not.

OK, so we can recognize whether something is an example of matter, but we would also like to know something about the composition of matter (as indicated in the second definition of chemistry above). When we use the term composition we mean what is it made of, or what is in it? In terms of the nonchemist a friend might introduce us to a new food or drink, and we might ask (if we really like it, or if we really dislike it), "What is in that stuff?" We want to know somethng about the composition.

For a chemist matter is either pure or it is a mixture. If the sample is a pure substance that means it has a fixed composition and distinct physical and chemical properties. If the sample is not pure then the sample is a mixture. A mixture is a combination of two or more substances where each substances retains its chemical identity (its physical and chemical properties).

I've introduced some new terms...physical and chemical properties...and we'll hold for just a moment before explaining these concepts. I'd like to cover some more ideas related to pure substances and mixtures first as that will get us into elements, compounds, atoms and molecules.

An element is an example of matter which consists of only one kind of atom, either individually or combined into larger units. Atoms are the smallest particles of an element that retain the chemical properties of the element. When we think of an atom I'd like you to think of a spherical shaped object (like a ball). Since an element contains only one kind of atom it is classified as a pure substance.

Molecules are units of matter consisting of two or more atoms combined in a definite ratio. When the atoms are the same in a molecule the substance is an element. When the atoms are different the substance is considered a compound. Another way of defining a compound is a pure substance containing more than one kind of atom.

Chemists have a list of elements and a much, much longer list of compounds. The list of elements is found in the periodic table. The list of compounds is too long to even think about listing here. There are millions of compounds which contain the limited number of elements found in the periodic table.

So do you know any elements? Here are some names of some elements;

carbon, hydrogen, oxygen, gold, and mercury

In the periodic table the elements are listed by one or two letter combinations. The one or two letter combinations are referred to as the symbol for the element. For the elements listed about the symbols are;

I'll expect you to memorize the name and the symbols of the first 20 elements, plus about thirteen additional common elements. What are the common elements? Listen carefully in class. When you've memorized these element names (correct spellings) and symbols try the self-test.

Let's return to the five elements listed above and talk about them briefly. When we look at a sample of carbon we find it is a pure substance containing carbon atoms. Interestingly enough there are three different forms of carbon; diamond, graphite and fullerene. When an element exists in different forms/arrangements those different arrangements are called allotropes. So diamond, graphite and fullerene are three allotropic forms of carbon.

Hydrogen and oxygen are interesting because when we look at samples of these two elements we find molecules of hydrogen and molecules of oxygen. Recall that a molecule is matter consisting of two or more atoms. Hydrogen molecules contain two hydrogen atoms 'bonded' together. Oxygen molecules contain two oxygen atoms 'bonded' together. samples of gold and mercury, like carbon contain only atoms...no molecules of gold or mercury are found in samples of the elements.

So how do we communicate the difference between an element which contains only atoms and an element which contains only molecules. We use a formula to represent the nature of types of units (atoms or molecules) of which the element is composed. A chemical formula provides the symbol and a subscripted number to indicate the number of the atoms of the particular element. The subscript is always to the right of the element. Since graphie and diamond are composed of carbon atoms the symbol, C, and formula, C, are the same. The formula for hydrogen, H₂, and oxygen, O₂, is different from the symbol for these elements. Finally the formula and the symbol for gold and mercury are the same.

I'll expect you to know the formula for ALL of the elements in the periodic table. This is really not too bad. For the majority of the elements in the periodic table the symbol and the formula are the same, except for hydrogen, nitrogen, oxygen, fluorine, phosphorus, sulfur, chlorine, bromine and iodine. Can you find these formulas?

Try this Self-Test (just click on the image) before class.

A mixture is a combination of two or more substances where each substances retains its chemical identity (its physical and chemical properties). Mixtures are either heterogeneous or homogeneous. (I'll probably show you some examples in class.)

• heterogeneous mixtures do not have the same composition, properties or appearance.

• homogeneous mixtures do have the same composition, properties or appearance.

Matter is either a pure substance or a mixture. With all the different pure substances and mixtures how to we characterize the differences so we can know what is what. How is the element sulfur different from the element mercury? One way is to record the physical properties of the material. Physical properties are properties that can be measured and observed without changing the identity of the substance.

1. State(gas, liquid and solid) another example using water

2. Color

3. Melting Point (Important to note that a change in phase, which occurs at the boiling point or melting point of a substance does not necessarily mean a chemical change has occurred.)

4. Boiling Point

5. Density

6. Texture

7. Hardness

   Also important are

8. Mass

9. Volume

   but these properties have less to do with distinguishing between substances.

Examples of physical properties of matter.

	The obvious physical properties are that sulfur is a yellow solid (rhombic sulfur). Less obvious but which we can locate in a reference book or textbook is that sulfur has a melting point of 112.8 C and boils at 444.6 C. Several allotropic forms exist. Orthorombic sulfur density is 2.069 g/cm3, monoclinic (at 95 C) has a density of 1.94 - 2.01 g/cm3 .
	Silvery, heavy, moveable liquid. Its melting point is -38 C, boiling point is 356 C. It has a very high density at 13.5 g/cm3. Mercury is readily enhaled. It is not so much of a hazard when ingested. Spilled mercury should be cleaned up immediately to prevent long term, low-level exposure.
	Iodine is black looking solid at room temperature and readily sublimes to a violet vapor. The solid has a metallic luster and forms plates or scales. The vapor is corrosive with a sharp odor. Its melting point is 114 C, boiling point is 184 C and it has a density of 4.94 g/cm3. Iodine is not very soluble in hot or cold water, but it is soluble in solvents like alcohol, benzene and ether. Iodine is found in seawater. Ingestion of 2 to 4 grams have been known to be fatal.
	Nitrogen dioxide, NO2, is a brownish-red gas at room temperature. It is sealed in the glass tube to confine it and to protect us. Nitrogen dioxide is a poisonous gas. In the Merck Index Nitrogen dioxide is described as an 'insidious gas'. The gas can be fatal at a level of 200 ppm, and dangerous at 100 ppm. Its melting point is -9.3 C and it boils at 21 C. Its density is 3.3 grams/liter.

In class we looked at, and or discussed some physical properties of the following elements; nitrogen, oxygen, chlorine, bromine, lithium, sodium, potassium and mercury. Here are some additional pictures of these elements. (Remember you must know the Name and Password to access these Copyrighted pictures. If you missed class on friday or did not get this info, email me.)

I'll expect you to know the phase of ALL of the elements in the periodic table. This is the phase of every element at room temperature (25 degrees Celsius). So you will know at least physical property for every element. I'll expect you to know some other physical properties for some elements. For example of the elements above I'd epect you to recall their color as well as their phase. I would not expect you to remember details like boiling point or melting point, but I would like you to know that iodine sublimes.

Chemical properties for a pure substance are properties related to the chemical reactivity of the substance. Does the pure substance react with some other pure substance? What are some characteristic behaviors that help us decide whether a change is chemical or physical?

Experience and observation are essential in identifying chemical changes so we can determine chemical properties for a substance.

What should we look for to know a chemical change has occurred?

• a change in color;

• a solid forms;

• bubbles form (gas is produced);

• heat and/or flame is produced, or heat absorbed.

There are some changes which are not considered chemical. Freezing water, boiling water...not chemical changes, but physical changes. Why? The water is not changed. We started with water and we have water in the end. Adding a solid like sodium chloride to water and watching it dissolve is not a chemical change. Yes I know the sodium chloride disappears. But if we allow the water to evaporate we get the sodium chloride back. Most important for a chemical change is that new substances are formed. How do we tell if a new substance is formed? Well I guess we should use some fancy instruments to tell us the substance formed is different from the beginning substances. But we do not have these fancy instruments, so we'll use our eyes and our chemical intuition to tell us there is a chemical change. I'll be doing some chemical reactions in class so you can see a chemical change.

In class we viewed and discussed some chemical properties for the elements, lithium, sodium, potassium, rubidium, cesium, iron, aluminum, fluorine, bromine, oxygen, helium and neon. Here are some movies of the reactions of some of these elements. (Remember you must know the Name and Password to access these Copyrighted pictures. If you missed class on friday or did not get this info, email me.)

It was a gentleman by the name of John Dalton who organized a collection of experimental observations into a theoretical framework. Dalton, who was a meteorologist, had considerable experience with air and wind and the effects of temperature on the volume of a gas. The results of his study of air suggests that his observations could be understood if matter consisted of tiny particles, a sort of submicroscopic billiard ball. So Dalton proposed his atomic theory to explain his observations. Each element is made up of tiny, indivisible particles called atoms.

1. All atoms of a given element possess identical properties.

2. Atoms of different elements have different properties.

3. Chemical changes involve the combination, separation or rearrangement of atoms: atoms are neither destroyed, created or changed.

4. When atoms combine they do so in fixed ratios of whole numbers forming particles called molecules.

What is the microscopic model of the three phases of matter?

Here is an atomic level exercise from our first Problem Set.

(Note: To run the atomic level exercise the version of Netscape Navigator must be accessorized with the MacroMedia ShockWave Plugin. If Netscape displays a broken icon after clicking on the link above, then you need to download the plugin and install it. To download the plugin go to the Shockwave site and follow the instructions. The computers on campus should run the exercise no problem. If there is let me know. For those of you at home, download the plugin. There is a Mac and a PC version. So be sure to specify your platform when you are at the MacroMedia Web Site.)

Here are some additional notes about important terms you must understand, and be able to apply.