Science 122 Program 25 Atomic Theory

# Laws of Chemistry &Atomic TheoryProgram 25Lesson 4.3

## Coming Up

Before we're done with this program we will have learned about the laws of chemistry and how they led an opinionated schoolmaster named John Dalton to formulate a new theory of atoms based on the quantitative laws. We will learn about the law of combining volumes and the ensuing controversy which was finally resolved after Dalton's death by Avagadro's hypothesis with an elegance we have come to expect.

At the end of the program we will turn our attention to chemical symbols and equations.

## 2. Laws of Chemistry

### 2.3. Multiple Proportions

If two elements combine to form two or more different compounds, then a simple ratio exists between the two weights of one element that can combine with a fixed weight of the other

## 5. Law of Combining Volumes (Gay-Lussac's Law)

### 5.6. Dalton had worked with the gases on a weight basis and had worked out the relative weights of the atoms, but Gay-Lussac was convinced that the results are unrelated to weights, but rather a characteristic of the gaseous state

#### 5.6.1. Dalton believed the atoms were surrounded by caloric, so how could 3 or 4 volumes be compressed into two?5.6.2. There was no reliable model for the gaseous state of matter. Kinetic theory of gases was 40 years away

Italian of noble birth, practiced law but abandoned it to teach physics at the University of Turin due to his love of mathematics and physics.

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## 10. Summary and Conclusions

In this lesson we have seen how quantitative measures of chemicals in reactions led to basic laws, know today as The Laws of Conservation of Mass ,Definite Proportions, and Multiple Proportions . Dalton's atomic theory provides a rational and ingenuous explanation for the observed laws. Although Dalton's original version contained some errors, our modern atomic theory recognizes a few other basic laws which make the theory consistent. One of these is the Law of Combining Volumes, stated by Joseph Guy- Lussac, which notes that the volumes of products and reactants of reacting gases always occur in small integer ratios. Avagadro added the idea that equal volumes of gases contain equal numbers of molecules. Avagadro noted that certain elemental gases are diatomic.

With these laws chemists of the nineteenth century were able to calculate atomic weights very accurately by measuring the weight ratios of elements which reacted with either oxygen or hydrogen.

Further advances in chemical knowledge occurred when the modern system of chemical symbols was combined with a shorthand for describing chemical reactions. These equations provide an easy way to predict the weights of substances undergoing chemical reactions. These equations help us to understand many things about chemical reactions and properties, including the ability to predict the amounts of chemicals used in various reactions. They also help us to understand chemical changes in the world around us.

The large number of chemical substances which are know to us requires a system of naming. For simple compounds the naming is straightforward, but it works well even for the most complicated substances.

The confirmation of the atomic theory led to more questions about the nature of matter, specifically the relationship between the physical properties of atoms. Since matter is made of atoms, then atoms themselves should obey Newton's laws.