Early Ideas About Matter

Real-World Reading Link A football team might practice and experiment with different plays in order to develop the best-possible game plan. As they see the results of their plans, coaches can make adjustments to refine the team s play. Similarly, scientists over the last 200 years have experimented with different models of the atom, refining their models as they collected new data. 

Science as we know it today did not exist several thousand years ago. 

No one knew what a controlled experiment was, and there were few tools for scientific exploration. In this setting, the power of the mind and intellectual thought were considered the primary avenues to the truth. Curiosity sparked the interest of scholarly thinkers known as philosophers who considered the many mysteries of life. As they speculated about the nature of matter, many of the philosophers formulated explanations based on their own life experiences. 

While a number of Democritus s ideas do not agree with modern atomic theory, his belief in the existence of atoms was amazingly ahead of his time. However, his ideas were met with criticism from other philosophers who asked, What holds the atoms together Democritus could not answer the question. 

Aristotle Other criticisms came from Aristotle (384-322 b.c.), one of the most influential Greek philosophers. He rejected the notion of atoms because it did not agree with his own ideas about nature. One of Aristotle s major criticisms concerned the idea that atoms moved through empty space. He did not believe that empty space could exist. His ideas are also presented in Table 4.1. Because Aristotle was one of the most influential philosophers of his time, Democritus s atomic theory was eventually rejected. 

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Early Ideas About Matter Development of the Modern Atomic Theory The Discovery of Atomic Structure Atomic Numbers and Masses MiniLab 2.1 A Penny for Your Isotopes ChemLab Conservation of Matter... 

The Greek philosophers thought that air, earth, fire, and water were the elements that formed all matter. Notice how the properties hot, dry, cold, and wet are associated with each element. These early ideas about the elements were not completely swept aside until the 19th century. 

Matter comes in many shapes, sizes, and colors that are interesting to look at and describe. Early chemists did little more than describe what they observed, and their chemistry was a descriptive science that was severely limited in scope. It became a much more useful science when chemists began to make quantitative measurements, do calculations, and incorporate the results into their descriptions. Some fundamental ideas about matter are presented in this chapter, along with some ideas about quantitative measurement, the scientific measurement system, and calculations. 

Early Ideas about the Building Blocks of Matter... 

You have seen how scientists in the late nineteenth and early twentieth century developed and modified the atomic model. Changes in this model resulted from both experimental evidence and new ideas about the nature of matter and energy. By 1913, chemists and physicists had a working model that pointed tantalizingly in a promising direction. During the third decade of the twentieth century, the promise was fulfilled. In the next section, you will learn how physicists extended the ideas of Planck, Einstein, and Bohr to develop an entirely new branch of physics, and a new model of the atom. 

The atom as an ultimate and indivisible particle of matter was a venerable and a viable scientific notion for many years before and after Daltoa For example, Newton s speculations about matter in the Queries at the end of his Opticks included Particles so very hard, as never to wear or break in pieces no ordinary Power being able to divide what God himself made one in the first Creation (Newton, I. Opticks, London, 1704 Query 31). This chapter describes ideas and scientific evidence from the late 19 and early 20 centuries about the contrary notion, the divisibility of atoms. It is about the notion that the ultimate pieces of matter themselves have pieces. It focuses on the electron and the nucleus, with a few words about the proton and neutron as well it does not treat constituent pieces of nucleons and more exotic particles. 

As early as 400 BCE, a few people believed in an atomic theory, which states that atoms are the building blocks of all matter. Yet until recently, even scientists had never seen evidence of atoms. Experimental results supporting the existence of atoms did not appear until more than 2000 years after the first ideas about atoms emerged. The first of these experimental results indicated that all chemical compounds share certain characteristics. 

Element The most fundamental form of matter at a chemical level. The great range of ideas about elements and what substances should be considered elements has driven chemical research for much of the history of civilization. Early thinkers generally assumed that there was a small number of elements (from 1 to 5), but today we recognize about 110 naturally occurring and artificial elements found on the Periodic Table of Elements. 

By the early 1800s, the Law of Conservation of Matter (Section 1-1) and the Law of Definite Proportions (Section 1-5) were both accepted as general descriptions of how matter behaves. John Dalton (1766-1844), an English schoolteacher, tried to explain why matter behaves in such systematic ways as those expressed here. In 1808, he published the first modern ideas about the existence and nature of atoms. Dalton s explanation summarized and expanded the nebulous concepts of early philosophers and scientists more importantly, his ideas were based on reproducible experimental restdts of measurements by many scientists. These ideas form the core of Dalton s Atomic Theory, one of the highlights in the history of scientific thought. In condensed form, Dalton s ideas may be stated as follows ... 

The Greek philosophers are the first people on record to have thought deeply about the nature of matter. As early as 600 b.c., these scholars wanted to know the why of things. However, they were immersed in the philosophical thought of their day that held that physical reality is an imperfect representation of a more perfect reality. As a result, they did not emphasize experiments on the imperfect physical world as a way to understand it. According to Plato (428-348 b.c.), reason alone was the superior way to unravel the mysteries of nature. Remarkably, Greek ideas about nature led to some ideas similar to modem ones. 

The next great development in physics was again an outgrowth of Einstein s ideas. Dirac was not satisfied with the fact that early quantum mechanics did not fit into the framework of relativity theory, The velocities of electrons in ordinary atoms are so small compared to the speed of light that the neglect of relativity theory did not matter much. Rut what about wave mechanics of particles that move much faster Dirac was able in 1927 to unite relativity with quantum mechanics. 

D. E. Koshland and J. T. Edsall have recorded their own experiences in early protein research. Koshland stresses the value of his induced fit theory,192 while Edsall describes his long career at Harvard after two years with Hopkins at Cambridge.193 Fruton has also described the work of T. B. Osborne (1859-1928), noted for his analyses of amino-acids from seed proteins.194 The idea that enzymes might be proteins was a matter of heated debate among chemists from about 1915, including arguments between Willstatter and James Sumner, who in 1926 isolated the enzyme urease and showed it to be a protein.195 However, while it is most important to emphasize protein chemistry, the contributions made to protein science by physics... 

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