Moles counting atoms

How much is a mole Why is Avogadro s number used when counting atoms but not in counting everyday amounts ... 

The mole is literally the chemist s dozen. Just as egg farmers and grocers use the dozen (a unit of 12) to count eggs, chemists use the mole (a much larger number) to count atoms, molecules, or formula units. When farmers think of two dozen eggs, they are also thinking of 24 eggs. 

The mole is used to help us count atoms and molecules. The relationship between moles, number of particles, and the Avogadro constant is... 

How can you use this relationship to relate mass and moles The periodic table tells us the average mass of a single atom in atomic mass units (u). For example, zinc has an average atomic mass of 65.39 u. One mole of an element has a mass expressed in grams numerically equivalent to the element s average atomic mass expressed in atomic mass units. One mole of zinc atoms has a mass of 65.39 g. This relationship allows chemists to use a balance to count atoms. You can use the periodic table to determine the mass of one mole of an element. 

Using the mole concept and the periodic table, you can determine the mass of one mole of a compound. You know, however, that one mole represents 6.02 x 1023 particles. Therefore you can use a balance to count atoms, molecules, or formula units ... 

The meaning of a chemical formula was discussed in Chapter 5, and we learned how to interpret formulas in terms of the numbers of atoms of each element per formula unit. In this chapter, we will learn how to calculate the number of grams of each element in any given quantity of a compound from its formula and to do other calculations involving formulas. Formula masses are presented in Section 7.1, and percent composition is considered in Section 7.2. Section 7.3 discusses the mole—the basic chemical quantity of any substance. Moles can be used to count atoms, molecules, or ions and to calculate the mass of any known number of formula units of a substance. Section 7.4 shows how to use relative mass data to determine empirical formulas, and the method is extended to molecular formulas in Section 7.5. 

The situation is similar in counting atoms, but much more difficult. Individual atoms cannot be seen to be counted, nor can they be weighed in the ordinary manner. Still, if the mass of 1 atom can be determined (in amu, for example) the number of atoms in a mole can be calculated. Historically, what chemists have done in effect is to weigh very large numbers of atoms of different elements where the ratio of atoms of the elements is known they have gotten the ratio of the masses of individual atoms from the ratio of the mass of the different elements and the relative numbers of atoms of the elements. 

Define mole, and explain why this unit is used to count atoms. 

If you could count two atoms every second, how long would it take you to count a mole of atoms Assume that you counted continually 24 hours every day. How does the time you calculated compare with the age of Earth, which is estimated to be 4.5 X 10 years old ... 

If you missed 16, go to Elements Moles and Counting Atoms, page 114. 

In the arithmetic of chemistry, a lot of calculations come down to counting atoms and molecules. The international unit for the amount of substance isn t the kilogram (which is used for mass), it s the mole. Chemists need to think in terms of numbers of particles, and this is what the mole allows. The mole is a very large number 6.022 x 1023. It is the number of carbon-12 atoms in exactly 12.00 grams of that isotope. It is such an important number in chemistry that it has its own special name, Avogadro s number, named after Amadeo Avogadro (1776-1856), one of the most famous early scientists. 

If you want to count atoms, Avogadro s number must be part of the solution. Keep in mind that 1 mole of any element represents 6.022 x 1023 atoms of that element. This fact provides the necessary equality to develop two conversion factors. In terms of iron, Fe ... 

Step 1. Count the number of moles of atoms of each element on both product and reactant side. 

QQI2KES Chemists use the mole to count atoms, molecules, ions, and formula units. 

Because samples of matter typically contain so many atoms, a unit of measure called the mole has been established for use in counting atoms. For our purposes it is most convenient to define the mole (abbreviated mol) as the number equal to the number of carbon atoms in exactly 12 grams of pure... 

Modern techniques that allow us to count atoms very precisely have been used to determine this number as 6.022137 X 10 (6.022 X 10 will be sufficient for our purposes). This number is called Avogadro s number to honor his contributions to chemistry. One mole of something consists of 6.022 X 10 units of that substance. Just as a dozen eggs is 12 eggs, a mole of eggs is 6.022 X 10 eggs. 

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