Compounds and Mixtures

Often times, matter that you see around you in everyday life isn't just a pure element. Just look around in your house and you more than likely wouldn't find any Sodium sitting around, but you most likely have table salt (sodium chloride) in your kitchen. How is that there are more substances out there than there are elements? The answer is that elements can combine to form chemical compounds and mixtures.

Atomic Number and Atomic Mass

What is it that makes element different from another? Earlier, we said that elements in the same group on the periodic table usually have similar properties. Let's take a look at a specific group, group 11.  As you can see here, copper (Cu), silver (Ag), and gold (Au) all reside in the same group. These elements do, in fact, have similar properties (all metals, shiny, malleable, conduct electricity well), but we all know that they are very different elements. Take, for instance, their colors. Copper is seen in coins, wires, pipes, and a ton of other things and has a brownish hue to it. Silver has that nice grey color that's, well, silvery. Gold has that familiar rich yellowish color. What makes these 3 similar elements different from each other and other elements? This answer can be very complicated depending on the context of why it's asked, but for our purposes the answer is simple; they all have different numbers of protons in their atomic nucleus.

Law of Mass conservation and Law of Definite Proportions

Let's say that you've built a house out of Legos. After completing your masterpiece using blocks of different sizes, shapes and colors, you found that you're whole house weighs 1 pound. After marveling at your creation for a bit, you decide you want a bridge instead of a house, so you use all the pieces from the house and make yourself a bridge. How much would this bridge weigh? It seems intuitive to say that the bridge would weigh 1 pound also. Since you used the same blocks used in the house, their weights would have to be equal.

This is he basic idea that describes the Law of Mass Conservation.

Different Kinds of Properties

All elements and compounds have properties. Properties are just things we use to describe matter. Examples of properties of elements and compounds are color, volume, absorption of light, temperature, and odor. There are many ways you can describe matter, and all properties are classified in two ways...

Intensive and Extensive

Properties are either intensive or extensive depending of whether the property changes with the amount of the substance.
Values of intensive properties don't change no matter how much of a substance you have. Examples are melting point, boiling point, density, and malleability.
Extensive properties do change with the amount of the substance. Examples: volume, area, momentum, and mass.

Physical and Chemical
Properties can also be classified as being either physical or chemical. This depends on whether the property changes the chemical makeup of the substance.
Physical properties are ones that don't change the chemical makeup of a substance. Examples are temperature, mass, solubility, brittleness, density, and viscosity.
Chemical properties are ones that you notice when a substance undergoes a chemical reaction, changing it's chemical makeup. Examples: rusting, combustibility, and toxicity.  

Groups of the Periodic Table

There is an amazing amount of order that is in the periodic table. The more you learn about chemistry the more amazing it seems that the elements have been arranged in such a way. There are many similar properties that are observed across certain elements, and some of the properties are very evident in the groups (columns) of the periodic table. Let's take a look.

Elements and the Periodic Table

Everything that you see around you is composed of one or more of the known elements. But what are these elements?

An element is a fundamental substance that can't be broken down further through chemical or physical means. This means that there is a base unit of elements, ans that is the atom. Atoms cannot be chemically changed, and are the tiniest unit of an element. We'll talk more about atoms in a later post.

What we're focusing on here, is being able to read the periodic table of elements.