Introduction to the Periodic Table

The percent isotopic abundances must total 100%, and the fractional isotopic abundances must total 1. If we let/ represent the fractional abundance of Br, then the fractional abundance of Br is 1 —/. Therefore, we may write 

An atomic mass of 79.901 u irrmlies that the percent isotopic abundance of Br is 50.817%. Therefore, the percent isotopic abundance of Br is (100 50.817)% =49.183%. 

The percent isotopic abundance of Br is 50.516%, and the percent isotopic abundance of Br is 

These results indicate that the percent isotopic abimdance of Br varies between 50.516% and 50.817%. Because of this variation, the atomic mass of bromine is best expressed as an atomic mass interval. When a representative value of the atomic mass of Br is required, we wordd use the conventional atomic mass (Table 2.2) 

PRACTICE EXAMPLE A The masses and percent isotopic abundances of the three naturally occurring isotopes of silicon are Si, 27.9769265325 u, 92.223% Si, 28.976494700 u, 4.685% °Si, 29.973377017 u, 3.092%. Calculate the weighted-average atomic mass of silicon. 

The horizontal rows in the table are referred to as periods. The first period consists of the two elements hydrogen (H) and helium (He). The second period starts with lithium (Li) and ends with neon (Ne). 

The vertical columns are known as groups. Historically, many different systems have been used to designate the different groups. Both Arabic and Roman numerals have been used in combination with the letters A and B. The system used in this text is the one recommended by the International Union of Pure and Applied Chemistry (lUPAC) in 1985. The groups are numbered from 1 to 18, starting at the left. 

The numbers at the left of the rows are the period numbers. The black line separates the metals from the nonmetals. (Note A complete periodic table Is given Inside the front cover.) 

Other periodic tables label the groups differently, but the elements have the same position. 

You ll have to wait until Chapter 7 to learn why the second digit of some group numbers are In bold type. 

AIMS To learn about various features of the periodic tabie. To iearn some of the properties of metais, nonmetais, and metaiioids. 

In any room where chemistry is taught or practiced, you are almost certain to find a chart called the periodic table hanging on the wall. This chart shows all of the known elements and gives a good deal of information about each. As our study of chemistry progresses, the usefulness of the periodic table will become more obvious. This section will simply introduce it. 

Notice that elements 110 through 112, and element 114, have unusual three-letter designations beginning with U. These are abbreviations for the systematic names of the atomic numbers of these elements. Regular names for these elements will be chosen eventually by the scientific community. 

Mendeleev actually arranged the elements in order of increasing atomic mass rather than atomic number. 

Throughout the text, we wiii highiight the iocation of various eiements by presenting a smaii version of the periodic tabie. 

OBJECTIVES To learn about various features of the periodic table. 

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Almost all chemistry classrooms have a chart called the periodic table hanging on the wall. It shows all the chemical elements and contains a great deal of useful information about them. As we continue our study of chemistry, we will learn much more about the periodic table. For now let s begin with the basics. 

A simple version of the periodic table is shown in Table 3.5. Notice that in each box there is the symbol for the element and, above it, a number called the atomic number. For example nitrogen is 

The elements are placed in the table in order of increasing atomic number in a particular arrangement designed by Dimitri Mendeleev in 1869. Flis arrangement organizes the elements with similar chemical properties in columns called families or groups. An example of this is the column in the margin. 

These elements are all gases and nonreactive. The group is called the noble gases. Other groups with special names are the alkali metals (under lA on the table), alkaline earth metals (Group 2A), and halogens (Group 7A). 

Some groups of elements have special names. 

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This introduction to the periodic table only touches the surface of its usefulness. In the next section, you will discover how an element s electron configuration, which you learned about in Chapter 5, is related to its position on the periodic table. 

Lesson 1 Lesson 2 Lesson 3 -Introduction to the Periodic Table. -Variations in atomic and ionic radii across Period 3. -Variations in melting points and electrical conductivities across Period 3 Regular instruction - expository, questioning and group discussion. 

This introduction to the periodic table touches only the surface of its usefulness. You can refer to the Elements Handbook at the end of your textbook to learn more about the elements in the various groups. 

Elementary chemical concepts and an introduction to the periodic table are clearly explained in the early chapters of ... 

Increased emphasis on atomic structure as the foundation of chemistry is achieved hy moving the atomic structure chapter to an earlier position, Chapter 4. That chapter includes an early, brief introduction to the periodic table. The key concept of chemical periodicity is then elaborated in more detail in Chapter 5. Instructors that wish to use an atoms first approach can easily start with Chapters 4 and 5, then return to stoichiometry concepts in Chapters 2 and 3. Because much of chemistry involves chemical reactions, we have introduced chemical reactions in a simplified, systematic way early in the text (Chapter 6). This placement allows us to build solidly on the ideas of atomic structure and chemical periodicity from the preceding two chapters. 

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