Another Look at the Periodic Table

It is time for another look at the periodic table. Recall from Unit 1 that the larger of the two numbers in each square is called the atomic mass of the element. Molar mass is the sum of the atomic masses of all the atoms in the formula of a compound or molecule. Remember to round these atomic masses to the nearest whole number. 

We mentioned in Section 1.3 that chemists simplify the task of studying the enormous quantity of different material substances that exist by placing them into classifications and subclassifications. Let us now take another look at the periodic table and see what subclassifications chemists have used for the elements. 

A closer look at the periodic table points out some interesting trends. These trends not only help us predict how one element might perform relative to another, but also give us some insight into the important properties of atoms and ions that determine their performance. For example, examination of the melting points of the elements in Table 1.3 shows that there is a general trend to decrease melting point as we go down... 

Another way to look at the periodic table is to divide the elements into metals, nonmetals, and metalloids. Most of the elements in the table are metals. Metals are usually shiny and can be bent, hammered, or pulled into many different shapes without breaking into pieces. Metals are also good conductors, which means that heat and electricity can pass through them easily. Metals tend to give up electrons when they react with other elements. From this information, one could guess that most metals are found on the left side of the table, where the valence electron shells are mostly empty. 

Looking at the periodic table confirms that the average atomic mass of lithium is 6.94 u. The upcoming Sample Problem gives another example of how to calculate average atomic mass. 

As youYe wondering what in the world these activities have to do with nuclear chemistry, ponder this question What holds the nucleus of an atom together Shouldnh all those positively charged protons push one another apart Next, take a look at the Periodic Table and see what happens to the number of protons and neutrons in an atom as the atoms increase in atomic number. In the smaller atoms, the numbers are equal. What happens after they are no longer equal ... 

Look at the periodic table on the inside back cover of this textbook. As you can see, there are more than 110 different elements. This means that there are more than 110 different kinds of atoms. What makes an atom of one element different from an atom of another element You know that all atoms are made up of electrons, protons, and neutrons. Thus, you might suspect that atoms somehow differ in the number of these particles. If so, you are correct. 

Another way of looking at these data is shown on Table IV. For this period 186 different companies submitted a total of 1,056 PMNs. Here you also can see that 6 companies representing only 3% of the total accounted for 289 or 28% of all... 

As mentioned earlier, there is another region in the 5 /10/5 column that is sensitive to the changes in fresh feed flowrate Fqb- This is located at tray 12 in the reactive zone where the steady-state gain (Fig. 10.8) is fairly large. Figure 10.10 shows the relay-feedback test and step test results for tray 12. The ultimate gain and ultimate period from the relay-feedback test look reasonable (Table 10.2), and the step test shows no inverse response behavior for... 

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