Introduction to the Modern Concept of Atomic Structure

If the atom were expanded to the size of a huge stadium, the nucleus would be only about as big as a fly at the center. 

What was it made of By 1919 Rutherford concluded that the nucleus of an atom contained what he called protons. A proton has the same magnitude (size) of charge as the electron, hut its charge is positive. We say that the proton has a charge of l-i- and the electron a charge of 1-. 

OBJECTIVE To understand some important features of subatomic particles. 

In this model the atom Is called a nuclear atom because the positive charge Is localized In a small, compact structure (the nucleus) and not spread out uniformly, as In the plum pudding view. 

A nuclear atom viewed in cross section. (The symbol means approximately.) This drawing does not show the actual scale. The nucleus is actually much smaller compared with the size of an atom. 

An important question arises at this point If all atoms are composed of these same components, why do different atoms have different chemical properties The answer lies in the number and arrangement of the electrons. The space in which the electrons move accounts for most of the atomic volume. The electrons are the parts of atoms that intermingle when atoms combine to form molecules. Therefore, the number of electrons a given atom possesses greatly affects the way it can interact with other atoms. As a result, atoms of different elements, which have different numbers of electrons, show different chemical behavior. Although the atoms of different elements also differ in their numbers of protons, it is the number of electrons that really determines chemical behavior. We will discuss how this happens in later chapters. 

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The Elements Symbols for the Elements Dalton s Atomic Theory Formulas of Compounds The Structure of the Atom Introduction to the Modern Concept of Atomic Structure Isotopes... 

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