How Do Atoms Combine with Each Other?

A couple of millennia ago, the Greeks believed that water was one of the four elements of nature, along with fire, air, and earth, and that all things were made from combinations of these elements. Today, we of course know that there are more than a hundred elements. And, in fact, water is not a single element but a combination of atoms of two elements, namely hydrogen (H) and oxygen (O). When two or more atoms of the same or different elements combine together, molecules are formed. Therefore, water is a molecule. The chemical formula for a water molecule (H2O) is probably the most widely quoted of all chemical formulas. A chemical formula is merely a molecule’s atomic recipe. Thus, for each molecule of water, two hydrogen atoms (subscript 2 behind H) are bound to one oxygen atom (no subscript, so 1 is implied).
 

From our previous description of the size of atoms you can imagine then that an ordinary glass of water must contain millions of water molecules. In fact, we can use water to tidy up our understanding of elements, atoms, and molecules. If we have an 8 ounce (oz) glass of pure water, we can say that the container is accommodating millions of molecules of water, and thus millions of atoms; however, only two elements are present, oxygen and hydrogen.

Atoms can link together or bond by two means. First, charged atoms can interact with oppositely charged atoms. Remember, as in so many aspects of life, opposites attract. Perhaps the best example of this kind of bonding is sodium chloride (NaCl) or common table salt. Here, the negatively charged chloride ions (Cl−) are attracted and electrically stick to positively charged sodium ions (Na+). You can also check your toothpaste for sodium fluoride (NaF) or toothpaste salt. By the way, the term salt is a general term that describes these types of electrical interactions

Na+ Cl− sodium chloride (table salt)
Na+ F− sodium fluoride (toothpaste salt)
 

Another way that atoms can bond with each other is by sharing electrons. This is a fascinating event whereby atoms share electrons between them to form a stable union. In Figure 1.3 and throughout this book you will see a straight line connecting atoms that are bonded in this manner. Probably the best examples of this type of bonding are the so-called organic molecules, which refers to those molecules that contain carbon atoms. Organic also refers to that which is living. Therefore, the most important molecules of life must be carbon based. In fact, a large portion of this book discusses organic molecules, such as proteins, carbohydrates, fats, cholesterol, nucleic acids, and vitamins.

Can Certain Atoms Have a Charge?

Atoms of certain elements naturally exist in a charged state, which means that they have either lost or gained electrons. It really is a matter of simple algebra. If an atom exists without an electron, it will have a single positive charge (1+) and if it exists without two electrons it will develop a double positive charge (2+). On the contrary, if an atom has an extra electron, it

will have a single negative charge (1−) and if an atom has two additional electrons it will have a double negative charge (2−). It is important to keep in mind that this isn’t random; some atoms are simply more stable in a charged state. Charged atoms are often called electrolytes because their charge gives them electrical properties as discussed further below. The processes of losing and gaining electrons are interrelated, as displayed in Figure 1.2. So, if one atom gains an electron, it is actually removing the electron from another atom which wants to give it up to become more stable. This activity is referred to as oxidation and reduction, whereby oxidation refers to the loss of an electron while reduction refers to the gain of an electron. You might be thinking that this may have

something to do with antioxidant nutrients, such as vitamins C and E and a whole host of others such as β-carotene and lycopene. If you were, then you are right and have the mind of a scientist. Furthermore, you may have heard the term oxidation used in reference to energy operations in our body (for example, oxidation of fat). Again, you would be on the right track—but we are getting ahead of ourselves.
 

Oxidation refers to when an atom or molecule loses an electron. Many elements important to nutrition and the proper functioning of our body exist naturally in a charged state. These elements include sodium, chlorine, potassium, iodine, magnesium, and calcium. The charge associated with an atom is often displayed in superscript next to the element’s symbol from the Periodic Table of Elements. For instance, sodium is written as Na+, potassium as K+ (both of which have given up an electron, while calcium is written as Ca2+ and magnesium as Mg2+ as they have given up two electrons. On the contrary, chlorine is written as Cl−, fluorine as F− and iodine as I− as they have gained an electron and thus a negative charge. Actually, we tend to refer to chlorine, fluorine, and iodine as chloride, fluoride, and iodide with respect to this electrical state.

What Is the Relationship Between Elements and Atoms?

Atoms are the building blocks of everything that exists. From the clothes on your back to the car you drive to the food you eat—everything is composed of atoms. Each individual atom belongs to only one element. This is to say that even though there are an incomprehensible number of atoms on this planet and the universe making up everything we know and are yet to know, all of these atoms belong to only one of a hundred or so
elements (see Appendix A). This is similar to each one of the billions of people living on this planet being native to only one of a hundred or so countries.
 

In a world where size is judged relative to the size of humans, the atom is indeed minuscule. It has been said that if we could line up a million atoms end to end they would barely cover the distance across the period at the end of this sentence. However, they do indeed exist even though you cannot see them with the naked eye.
 

All atoms have a similar blueprint to the image displayed in Figure 1.1. There are three principal particles called neutrons, protons, and electrons. Because they are smaller than the atom that they come together to form, they are often called subatomic particles. Protons bear a positive charge (+) while electrons have a negative charge (−) and neutrons do not bear any charge at all. By design an element has the same number of electrons as protons and is said to be neutral. However, as we’ll see next that isn’t how many atoms exist naturally.