How Atoms Differ

Look at the periodic table on the inside back cover of this textbook. As you can see, there are more than 110 different elements. This means that there are more than 110 different kinds of atoms. What makes an atom of one element different from an atom of another element You know that all atoms are made up of electrons, protons, and neutrons. Thus, you might suspect that atoms somehow differ in the number of these particles. If so, you are correct. 

Remember that because all atoms are neutral, the number of protons and electrons in an atom must be equal. Thus, once you know the atomic number of an element, you know both the number of protons and the number of electrons an atom of that element contains. 

Atomic number = number of protons = number of electrons 

For instance, an atom of lithium, atomic number of 3, contains three protons and three electrons. How many electrons does an atom of element 97 contain  

The atomic number of an element equals the positive charge contained in its nucleus. 

QOnilES The number of protons and the mass number define the type of atom. 

Real-World Reading Link You are probably aware that numbers are used every day to identify people and objects. For example, people can be identified by their Social Security numbers and computers by their IP addresses. Atoms and nuclei are also identified by numbers. 

As shown in the periodic table of the elements inside the back cover of this textbook, there are more than 110 different elements. What makes an atom of one element different from an atom of another element  

Not long after Rutherford s gold foil experiment, the English scientist Henry Moseley (1887-1915) discovered that atoms of each element contain a unique positive charge in their nuclei. Thus, the number of protons in an atom identifies it as an atom of a particular element. The number of protons in an atom is referred to as the atomic number. 

It is important to be able to obtain usefiil information from the periodic table. Starting with the simplest element, hydrogen, the periodic table represents each element in a box. 

Atoms have no net electrical charge because they contain equal numbers of electrons and protons. Thus, positive charges (protons) and negative charges (electrons) balance out. Electrons, protons, and atomic number are related as follows. 

Identify the atom containing the following number of protons. 

Atoms of which element contain 18 protons and 18 electrons  

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Chemists are satisfied how atoms of the different elements could form from the initial enormous energy of the big bang explosion, without, however, the need to concern themselves with the reason for its origin. Atoms subsequently can combine into molecules, which in turn build increasingly complex systems and materials, including those of the living systems. This is the area of interest for chemists. 

Display water as a ball-and-spoke model. How many different vibrations are there Explain. One after the other, animate these vibrations. For each, record the vibrational frequency and provide a description of the atomic motions. What appears to be easier (lower frequency), motions primarily associated with bond stretching or with angle bending ... 

How many different products containing two carbon atoms are possible in the reaction of chlorine with ethane Do any of the products exist as optical isomers ... 

From an understanding of how atoms join to make molecules, chemists can explain why two compounds that seem so similar have profoundly different reactivity patterns. We describe how atoms link together in Chapters 9 and lO. Meanwhile, remember that chemists try to visualize chemical reactions at the molecular level. Contemporary chemists also manipulate individual atoms to make elaborate structures, as described in our Box. 

In this section, we will present the basis developed to explain the structure of solids. That is, the concepts that were perfected in order to accurately describe how atoms or ions fit together to form a solid phase. This work was accomplished by many prior workers who established the rationale used to define the structure of a symmetrical solid. As you will recall, we said that the basic difference between a gas, liquid and that of a solid lay in the orderliness of the solid, compared to the other phases of the same material. 

How many different ground states may an atom have ... 

O IfflD Explain how the quantum mechanical model of the atom differs from the atomic model that Bohr proposed. 

How does the arrangement of electrons around the central atom differ in PI3 and CII3 Draw the Lewis structures for these compounds to answer this question. 

There are a host of physical questions that cannot be easily answered just by knowing the rates listed in Fig. 6.13. For example, once an Ag atom is deposited on the surface, how long will it be (on average) before that Ag atom visits a site adjacent to a Pd surface atom How many different Pd surface sites will an Ag atom visit per unit time on the surface What is the net diffusion coefficient of Ag atoms on this surface To answer these questions, we need a tool to describe the evolution in time of a set of Ag atoms on the surface. 

The coefficient of the symmetry element, in the top line, tells how many different equivalent operations of this type occur. However, not all symmetry elements of the same type are always equivalent. Thus, in the symmetry group of benzene, the thirteen C2 operations fall into three distinct classes the one dyad perpendicular to the molecular plane, the six that pass through opposite atoms in the ring, and the six that pass in between the atoms, through the centers of the bonds. Each of these operations is equivalent only to the others within the same class. 

Atoms rarely exist as individual units. Atoms combine with each other to produce the familiar substances of everyday life. Chemistry is largely the study of how atoms combine to form all the different forms of matter. The reason atoms combine involves the subject of chemical bonding, which is explored in Chapter 7. In this chapter, the grouping of atoms into different types of compounds is examined. In the first half of the chapter, chemical nomenclature is discussed. Some of the basic rules for naming compounds are presented. Atoms combine and are rearranged through chemical reactions. The last half of the chapter examines the basic process of chemical reactions and classifies several different types of reactions. 

Let us first examine what happens to a crystal when we remove, add, or displace an atom in the lattice. We will then describe how a different atom, called an impurity (regardless of whether or not it is beneficial), can fit into an established lattice. As shown by Eq. (1.36), point defects have equilibrium concentrations that are determined by temperature, pressure, and composition. This is not true of all types of dimensional defects that we will study. 

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