Using Chemical Symbols

We have already used a few chemical formulas, comhinations of the symbols for the elements that represent the stable combinations of atoms in molecules for elemental hydrogen, H2O for water, and CjgHggOjj for 

Sometimes a line or lines are drawn between symbols to indicate which atoms are connected in molecules  

Theli nes in structural formulas represent chemical bonds, which we ll have much more to say about in Chapter 5. 

Organic compounds are so numerous and so important that they are the basis for an entire field of chemistry—organic chemistry (Chapters 12 and 14). Most compounds produced by living things, most medicines, and the components of most plastics are organic compounds. 

Formulas that show the connections in this way are known as structural formulas, whereas formulas that give just one symbol for each element present are called molecular formulas. The molecular formula for methane is GH, for example. Methane and the many millions of compounds that contain carbon combined with hydrogen— and often also with nitrogen, oxygen, phosphorus, or sulfur—are known as organic compounds. 

---

Chemical equations can also be written using chemical symbols. Chemical symbols are a shorthand way to write the name of an element. The chemical symbol for hydrogen is H, and the chemical symbol for oxygen is O. 

The reactant side of this chemical equation, using chemical symbols looks like this ... 

Remember that a chemical formula uses chemical symbols and numbers to show the kinds of atoms of each element that are joined together. The chemical formula for water is HaO. This means that two atoms of hydrogen are chemically joined to one atom of oxygen to make a molecule of water. A molecule is the smallest unit of a chemical compound that still has the same chemical properties of the compound. When there is only one atom in a molecule, such as the oxygen in water, the numeral 1 is not written but is just assumed to be there. 

Chemical formula A written expression using chemical symbols and numbers to show how atoms are joined. 

A chemical change or chemical reaction can be described by writing a chemical equation. A chemical equation uses chemical symbols to show what happens during a chemical reaction. 

Having discussed the masses of atoms and molecules, we turn next to what happens to atoms and molecules in a chemical reaction, a process in which a substance (or substances) is changed into one or more new substances. In order to communicate with one another about chemical reactions, chemists have devised a standard way to represent them using chemical equations. A chemical equation uses chemical symbols to show what happens during a chemical reaction. In this section we will learn how to write chemical equations and balance them. 

Use chemical symbols for the various elements to write the skeletal structure of the compound. To accomplish this, place the bonded atoms next to one another. 

The identity of products and reactants must he specified using chemical symbols. In some cases it is possible to predict the products of a reaction. More often, the reactants and products must be verified by chemical analysis. (Generally, you will be given information regarding the identity of the reactants and products.)... 

Use chemical symbols together with atomic number and mass number to express the subatomic composition of isotopes. (Section 2.3)... 

The different isotopes of an element are distinguished by their mass numbers. For example, Ihe three naturally occurring isotopes of uranium are uranium-234, uranium-235, and uranium-238, where Ihe numerical suffixes represent Ihe mass numbers. These isotopes are also labeled, using chemical symbols, as and 92U. The superscript is Ihe mass number the subscript is Ihe atomic number. 

A chemical reaction, as described in the third hypothesis of Dalton s atomic theory [Ml Section 2.1 ], is the rearrangement of atoms in a sample of matter. Examples include the rusting of iron and the explosive combination of hydrogen and oxygen gases to produce water. A chemical equation uses chemical symbols to denote what occurs in a chemical reaction. We have seen how chemists represent elements and compounds using chemical symbols. Now we wDl look at how chemists represent chemical reactions using chemical equations. 

---