Atoms and Molecules

Is It really true???

Quantum Theory, in physics, description of the particles that make up matter and how they interact with each other and with energy. Quantum theory explains in principle how to calculate what will happen in any experiment involving physical or biological systems, and how to understand how our world works. The name “quantum theory” comes from the fact that the theory describes the matter and energy in the universe in terms of single indivisible units called quanta (singular quantum). Quantum theory is different from classical physics. Classical physics is an approximation of the set of rules and equations in quantum theory. Classical physics accurately describes the behavior of matter and energy in the everyday universe. For example, classical physics explains the motion of a car accelerating or of a ball flying through the air. Quantum theory, on the other hand, can accurately describe the behavior of the universe on a much smaller scale, that of atoms and smaller particles. The rules of classical physics do not explain the behavior of matter and energy on this small scale. Quantum theory is more general than classical physics, and in principle, it could be used to predict the behavior of any physical, chemical, or biological system. However, explaining the behavior of the everyday world with quantum theory is too complicated to be practical.

Quantum theory not only specifies new rules for describing the universe but also introduces new ways of thinking about matter and energy. The tiny particles that quantum theory describes do not have defined locations, speeds, and paths like objects described by classical physics. Instead, quantum theory describes positions and other properties of particles in terms of the chances that the property will have a certain value. For example, it allows scientists to calculate how likely it is that a particle will be in a certain position at a certain time.

Quantum description of particles allows scientists to understand how particles combine to form atoms. Quantum description of atoms helps scientists understand the chemical and physical properties of molecules, atoms, and subatomic particles. Quantum theory enabled scientists to understand the conditions of the early universe, how the Sun shines, and how atoms and molecules determine the characteristics of the material that they make up. Without quantum theory, scientists could not have developed nuclear energy or the electric circuits that provide the basis for computers.

Quantum theory describes all of the fundamental forces—except gravitation—that physicists have found in nature. The forces that quantum theory describes are the electrical, the magnetic, the weak, and the strong. Physicists often refer to these forces as interactions, because the forces control the way particles interact with each other. Interactions also affect spontaneous changes in isolated particles.

Why does salt dissolve in water and not gasoline?

This is a case of like dissolves like.

Water and salt both consist of what we call polar molecules. This means electrons in the molecule are not equally shared between the atoms of the molecule, causing a partial charge on the molecule's atoms.

Water, for instance, contains two hydrogen atoms and one oxygen atom. The electrons in the water molecule spend more time around the oxygen atom than around the hydrogen atoms.

Since electrons are negatively charged, the oxygen part of the molecule is partially negatively charged and the hydrogen parts of the atom are partially positively charged.

In salt, which is made of sodium and chlorine, the shared electrons spend almost all of their time on the chlorine side, making the chlorine negatively charged, and very little time on the sodium side, making the sodium positively charged.

When salt is put into water, the positively charged side of water molecules surround the negatively charged chlorine, and the negatively charged side of the water molecules surrounds the positively charged sodium. This breaks the sodium chloride bond and the salt is dissolved.

Gasoline contains non-polar molecules, which means the atoms in those molecules share electrons equally.

This also means there is no partial charge on those molecules to be attracted to the charges on the sodium or chlorine molecules of salt. Therefore, salt doesn't dissolve in gasoline.

ATOMS & MOLECULES

1. What is the World made up of?

The world is made up of all sorts of things. Just look around you. There are houses, cars, trees, and people. All these things are different shapes, sizes, and colors. Look closely at some of them. They are made from different materials. Some are hard and cold. Others are soft and warm. They may be wet or dry, rough or smooth. All these things look and feel different to us.

The different things in the world have two things in common. They are all made up of something, which means they have substance, and they all take up space. Anything that takes up space and has weight is called matter. So a pencil, a book, a house, a tree, the air and everything around you is matter. You are matter, too. Earth is all matter, and so are the stars through out the universe and the dust that drifts between them.



2. What is matter?

Imagine you could divide a drop of water or a grain of sand. Imagine you can divide them again and again, until the pieces are so small that you can no longer see them. Scientists can divide these tiny particles of matter even smaller under a powerful microscope. They divide them again and again, until the particles are so small that they can no longer be seen clearly, even under the microscope. Whatever in the end makes up matter is so small that we cannot see it. But everything in the world – animals, vegetables, minerals, solids, liquids, and gases – is made of matter.


Space and energy

Because space has no substance and obviously does not take up space, it does not qualify as matter. Neither does energy, which is the ability to do work.

However, matter and energy are not completely separate. Most scientists believe that matter and energy are two aspects of the same thing, like liquid water and ice are two aspects of water.

ATOMS AND MOLECULES!!!

Atoms and molecules

ATOMS AND MOLECULES!!!


Introduction
The molecular structure hypothesis - that a molecule is a collection of atoms linked by a network of bonds - was forged in the crucible of nineteenth century experimental chemistry. It has continued to serve as the principal means of ordering and classifying the observations of chemistry. The difficulty with this hypothesis was that it was not related directly to quantum mechanics, the physics which governs the motions of the nuclei and electrons that make up the atoms and the bonds. Indeed there was, and with some there still is, a prevailing opinion that these fundamental concepts, while unquestionably useful, were beyond theoretical definition. We have in chemistry an understanding based on a classification scheme that is both powerful and at the same time, because of its empirical nature, limited.
Reformulation of physics that enables one to pose and answer the questions "what is an atom in a molecule and how does one predict its properties?" These questions were posed in my laboratory where it was demonstrated that this new formulation of physics, when applied to the observed topology of the distribution of electronic charge in real space, yields a unique partitioning of some total system into a set of bounded spatial regions. The form and properties of the groups so defined faithfully recover the characteristics ascribed to the atoms and functional groups of chemistry. By establishing this association, the molecular structure hypothesis is freed from its empirical constraints and the full predictive power of quantum mechanics can be incorporated into the resulting theory - a theory of atoms in molecules and crystals.
The theory recovers the central operational concepts of the molecular structure hypothesis, that of a functional grouping of atoms with an additive and characteristic set of properties, together with a definition of the bonds that link the atoms and impart the structure. Not only does the theory thereby quantify and provide the physical understanding of the existing concepts of chemistry, it makes possible new applications of theory. These new applications will eventually enable one to perform on a computer, in a manner directly paralleling experiment, everything that can now be done in the laboratory, but more quickly and more efficiently, by linking together the functional groups of theory. These applications include the design and synthesis of new molecules and new materials with specific desirable properties.
The theory of atoms in molecules enables one to take advantage of the single most important observation of chemistry, that of a functional group with a characteristic set of properties. This document outlines and illustrates the topological basis of the theory and its relation to the quantum mechanics of an open system.

Atoms and Molecules

Welcome to the world of atoms and molecules