Chemical elements periodic table, 2,9, inside back cover

Information about an element s protons and neutrons is often summarized using the chemical notation shown in Figure 2.3. The letter X represents the atomic symbol for an element. (The atomic symbol is also called the element symbol.) Each element has a different atomic symbol. All chemists, throughout the world, use the same atomic symbols. Over the coming months, you will probably learn to recognize many of these symbols instantly. Appendix G, at the back of this book, lists the elements in alphabetical order, along with their symbols. You can also find the elements and their symbols in the periodic table on the inside back cover of this textbook, and in Appendix C. (You will review and extend your understanding of the periodic table, in section 2.2.)... 

Pure substances can themselves be divided into two types elements and compounds. Copper is an example of an element, a substance that cannot be broken down into simpler substances. The graphite in pencils is also an element—carbon. No chemical transformation can decompose graphite into simpler substances it is pure carbon. All known elements are listed in the periodic table in the inside front cover of this book and in alphabetical order on the inside back cover of this book. 

Carbon has two core electrons and four valence electrons (Table 1.2). Lithium and sodium each have one valence electron. If you examine the periodic table inside the back cover of this book, you will see that lithium and sodium are in the same column. Elements in the same column of the periodic table have the same number of valence electrons. Because the number of valence electrons is the major factor determining an element s chemical properties, elements in the same column of the periodic table have similar chemical properties. Thus, the chemical behavior of an element depends on its electronic configuration. 

For purposes of chemical bookkeeping, it is unnecessary to know the isotopic molar masses and isotopic distributions of the elements. All we need to know is the mass of one mole of an element containing its natural composition of isotopes. These molar masses usually are included in the periodic table, and they appear on the inside front and back covers of this textbook. 

Let s take a more detailed look at the periodic table and discover its great symmetry and usefulness. (Refer to the periodic table of chemical elements reproduced on the inside front and back covers of this book.)... 

Look at the periodic table hanging on the wall of your classroom or the one inside the back cover of your textbook. Notice that the elements are numbered from 1 for hydrogen, 2 for helium, through 8 for oxygen, and on to numbers above 100 for the newest elements created in the laboratory. At first glance, it may seem that these numbers are just a way of coimting elements, but the numbers mean much more than that. Each number is the atomic number of that atom. The atomic number of an element is the number of protons in the nucleus of an atom of that element. It is the number of protons that determines the identity of an element, as well as many of its chemical and physical properties, as you will see later in the course. 

Families of elements with similar chemical properties that lie in the same vertical column on the periodic table are called groups. Groups are often referred fo by the number over the column (see Figure 3.7). Note that the group numbers are accompanied by the letter A on the periodic table in Figure 3.7 and on the table inside the back cover of the text. For simplicity we will delete the A when we refer to groups in the text. 

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