Chemistry 101: Elements, Compounds, and Mixtures
- In This Quick Guide:
- The World of Elements
- Chemical Compounds
- Mixtures
- Colloids: Our Weird Friends
One of the things we chemists like to do is to organize everything into categories. This makes our lives easier because it allows us to remember the properties of classes of things rather than to remember the specific and individual properties of everything we come across. When dealing with materials, we typically classify things as being either elements, compounds, or mixtures.
The World of Elements
Elements are defined as substances that cannot be chemically decomposed into simpler substances. To understand what this somewhat confusing definition means, let’s discuss an example.
Gold is an element, as are all of the substances on the periodic table. If I have a block of gold, I can do a lot of things to it—I can melt it, I can dent it, and so forth. One thing I can’t do, however, is break the gold atoms down into simpler materials. As an element, the gold atoms are, for our purposes, indestructible.
Each of the boxes on the periodic table represents one of our elemental friends.
I’m not even going to try to tell you how many elements there are because new ones are being discovered all the time. At this point, 112 elements have been named, but there are several others that have been discovered that we still haven’t figured out what to call.
Chemical Compounds
Chemical compounds are materials which consist of elements bonded to one another in defined proportions. To understand this, let’s take the example of water, H2O.
When we talk about water, we’re always talking about H2O. Water never has the formula H4O or anything else—no matter what, it always has two atoms of hydrogen and one atom of oxygen. Because it always has the proportion of 2 H to 1 O, and because the hydrogen and oxygen atoms are chemically bonded to one another, water is a chemical compound.
Unlike an element, a compound can be broken down into simpler materials through the use of chemical reactions. For example, through a process known as electrolysis, water can be broken down into hydrogen gas (H2) and oxygen gas (O2).
Mixtures
Mixtures are materials that contain more than one type of element or compound. One example of a mixture is salt water—because it contains both water (H2O) and salt (NaCl), it’s a mixture. Other mixtures you may have come across include chicken noodle soup, pie, and the Dallas Cowboys.
Though there are a lot of different mixtures, we can further break down the classification of mixtures to include two different subcategories: homogeneous mixtures and heterogeneous mixtures. Let’s take a look at each:
- Homogeneous mixtures are mixtures in which the components are completely and evenly mixed with one another. An example of this is salt water. If you take a small portion of salt water from one side of a glass and another small portion of salt water from the other side of the glass, both will have identical ratios of salt to water. Other homogeneous mixtures you may be familiar with include air (where various gases are evenly mixed with one another), fruit punch (where sugar and various other compounds have been dissolved in water), and stainless steel (in which iron and various other elements are entirely mixed with each other).
- Heterogeneous mixtures are unevenly combined mixtures. If you take one sample of a heterogeneous mixture and another sample from a different part of the mixture, the two won’t be identical to one another. For example, if you were to take several samples from chunky peanut butter, in one you might find a brown paste and in another you might find a hunk of peanut. Frequently, you can tell a heterogeneous mixture from a homogeneous mixture because you can see that they contain different components, as is the case with stuffed animals, the Lincoln memorial, and punk rock legend Milo Aukerman.
Colloids: Our Weird Friends
Somewhere between homogeneous and heterogeneous mixtures lie the colloids. Colloids are heterogeneous mixtures which appear completely uniform in composition, but really just have one type of particle suspended in another without having been dissolved.
How does this happen? Well, let’s imagine that we have placed some very, very tiny particles of solid into water. If these particles are small enough, the water molecules that are in the liquid will hit them from all directions, keeping them from falling to the bottom of the container. Though the particles may be heavier than water, these collisions with the water molecules keep them from sinking.
Depending on what type of materials you have, there are several types of colloids:
- Aerosols are formed when liquid or solid particles are suspended in a gas. Cigarette smoke is an example of an aerosol.
- Foams are formed when gases are suspended in a liquid or solid. One tasty example of a foam is whipped cream.
- Emulsions are formed when particles of one liquid are suspended in another. Butter, for example, is an emulsion.
- Sols occur when solid particles are suspended in a liquid. Blood is an unpleasant example of a sol.
The best way to tell a colloid from a solution is to shine light on it. If the material seems cloudy, it’s a colloid, and if it’s clear, it’s a solution. This phenomenon is frequently exploited in horror movies where a minor character shines a light into a smoky room, only to be horribly killed.
Because we chemists like to make our lives easier, we classify materials as being either elements, compounds, or mixtures. Though each of these classes of materials have different properties, each of them is also vital to the study of chemistry. As you continue in your chemical studies, knowledge of these materials will come in very handy.
by Ian Guch, author of The Complete Idiot’s Guide to Chemistry, Third Edition
