Matter particle theory

The reason why classical mechanics is inadequate at the sub-atomic level is because it ignores quantum effects. Not only matter, but also radiation is discontinuous at the sub-microscopic level. Matter occurs as separate atoms and radiation as small packets, quanta or photons. At this level the two descriptions become identical - matter behaves like radiation and radiation behaves like matter. This is appropriate since matter and energy are interconvertible according to the relativistic relationship, E = me2. Wave and particle theories must therefore merge at the quantum level. 

Most of the universe is composed of plasma, a state of matter that exists at incredibly high temperatures (>5000°C). Under normal conditions, matter on Earth can only exist in the other three physical states, namely, the solid, liquid, or gaseous states. As you learned in an earlier course, the particle theory describes matter in all states as being composed of tiny invisible particles, which can be atoms, ions, or molecules. In this section, you will learn how these particles behave in each state. You will also learn about the forces that cause their behaviour. 

In previous courses, you learned about the properties of the different states of matter. You may recall that both solids and liquids are incompressible. That is, the particles cannot squeeze closer together, or compress. The incompressible nature of solids and liquids is not due to the fact that particles are touching. On the contrary, the particle theory states that there is empty space between all particles of matter. 

Another property of states of matter is their motion. According to the particle theory, all particles that make up matter are in constant motion. 

The particle theory of matter does not discuss the kinetic energy of particles. Kinetic energy is important, however, when describing the unique properties of gases. 

The particulate nature of matter is fundamental to almost every topic in chemistry. It involves the particle theory (often now called the kinetic molecular theory), which is the basis of explanations of atomic structure, bonding, molecules, much of solution chemistry and chemical reactions, equilibrium and chemical energetics. Because bonding (which involves atomic structure) and chemical reactions are covered in other chapters in this book, this chapter restricts itself to the particle theory of matter. Where useful, interesting aspects outside the particle theory are mentioned but the focus is fixed on the notion that all matter is composed of discrete, energetic particles that are separated by space. 

The idea that all substances can be separated into tiny indivisible particles called atoms, molecules and ions is widely accepted. Students are familiar with atoms and molecules per favour of the popular media and stylised atoms are the logo for several science TV programs (Johnston, 1990). Children are aware of atoms and molecules well before particle theory is taught in school (Lee et al., 1993). But this is where the similarity between science and student preconceptions ends because students consistently attribute the macroscopic properties of matter to its sub-microscopic particles (Albanese Vicenti, 1997). Similar alternative conceptions, which have given rise to the naive or attribution theory, have been reported in several studies. Seven features, that comprise commonly held alternative conceptions by school students, are now described. 

All science is based on a number of postulates. Quanmm mechanics has also elaborated a system of postulates that have been formulated to be as simple as possible and yet to be consistent with experimental results. Postulates are not supposed to be proved-their justification is efficiency. Quantum mechanics, the foundations of which date from 1925 and 1926, still represents the basic theory of phenomena within atoms and molecules. This is the domain of chemistry, biochemistry, and atomic and nuclear physics. Further progress (quantum electrodynamics, quantum field theory, and elementary particle theory) permitted deeper insights into the structure of the atomic nucleus but did not produce any fundamental revision of our understanding of atoms and molecules. Matter as described by non-relativistic quantum mechanics represents a system of electrons and nuclei, treated as pointlike particles with a definite mass and electric... 

An activity which illustrates this general point in relation to particle theory (the topic of Chapter 2) is included in a publication available from SEP (the Science Enhancement Programme, details of which are given in the Other resources section at the end of this introduction). The first of two group-work tasks in this activity Judging models in science asks students to consider two types of particle models - particles like tiny hard billiard balls particles as molecules with soft electron clouds - and to consider which model better explains a range of evidence based on the observable properties of matter. Students will find that each model is useful for explaining some phenomena, but neither fits all the evidence - and of course both models are stiU found useful in science. 

Because the extent of localization of the dressed photon is equivalent to the nanometric particle size, the long-wavelength approximation, which has always been employed for conventional light-matter interaction theory, is not valid. This means that an electric dipole-forbidden state in the nanometric particle can be excited as a result of the dressed photon exchange between closely placed nanometric particles, which enables the operation of novel nanophotonic devices. Details of such devices will be reviewed in Sect. 1.4. 

In 1924 Louis de Broglie (1892-1987) introduced ideas which were to revolutionise our concept of the electron and other fundamental particles. The quantum theory had proposed that electromagnetic radiation was particulate in some of its properties, but only a wave theory could explain diffraction. De Broglie proposed that both the wave and particle theories should be accepted. He also suggested that matter should be regarded as not only particulate in nature, but should also be considered to have a wave nature as well. The validity of this viewpoint was demonstrated in 1927 with Davisson and Germer s experimental observation of the diffraction of electrons by crystals. 

Paradigm shifts - the sub-atomic particle theory of matter... 

Historically, one of the key examples of this is the evaluation hy Einstein of the significance of Brownian motion, which led to the substantiation of the ideas behind the atomic theory of matter. Atomic theory was under challenge at the time from well-established and prestigious names within the scientific community. The phenomenon of Brownian motion and its interpretation was one major factor in the acceptance of the theory. Yet this acceptance involved interpretation of the unseen atomic world - the motion of sub-microscopic atoms and molecules - in terms of the motion of the seen world - the motion of smoke or dust particles under the microscope. 

The modern view of matter developed from John Dalton s theory which, for the first time, combined the abstractions of atom and element into a single practically useful concept, albeit at the cost of unwanted diversity. Resolution of the dilemma, by postulating hydrogen as the common building block of more complex atoms, was resisted so fiercely that the alleged author, William Prout, had to publish his proposal anonymously. The importance of number was at the heart of his hypothesis. Despite experimental evidence which contradicted the notion, Prout s hypothesis was not without support and remained alive until its final vindication in the discovery of isotopes and atomic number, which ironically also signalled the demise of atomic particle theory. 

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