Periodic table, 18

Periodic table Groups Alkali metals Alkaline earth metals Halogens Noble gases Transition metals Metals Nonmetals 

In any room in which chemistry is taught or practiced, you are almost certain to find a chart called the periodic table hanging on the wall. This chart shows all of the known elements and gives a good deal of information about each one. As our study of chemistry progresses, the usefulness of the periodic table will become more obvious. This section will simply introduce it. 

68 Chapter 3 Chemical Foundations Elements, Atoms, and Ions 

Note that the elements are listed on the periodic table in order of increasing atomic number. They are also arranged in specific horizontal rows and vertical columns. 

The elements were first arranged in this way in 1869 by Dmitri Mendeleev, a Russian scientist. Mendeleev arranged the elements in this way because of similarities in the chemical properties of various families of elements. For example, fluorine and chlorine are reacfive gases fhaf form similar compounds. 

The periodic table is an extremely useful tabulation of the elements. It is constructed so that each vertical column contains elements that are chemically similar. The elements in the columns are called groups, or families. (Elements in some groups can be very similar to one another. Elements in other groups are less similar. Eor example, the elements of the first group resemble one another more than the elements of the fourth group from the end, headed by N.) Each row in the table is called a period (Eig. 3-1). 

There are three distinct areas of the periodic table—the main group elements, the transition group elements, and the inner transition group elements (Fig. 3-2). We will focus our attention at first on the main group elements, whose properties are easiest to learn and to understand. 

The periods and the groups are identified differently. The periods are labeled from 1 to 7. Some reference is made to period numbers. The groups are referred to extensively by number. Unfortunately, the groups have been labeled in three different ways (Table 3-2)  

Classical Main groups are labeled lA through VIIA plus 0. Transition groups are labeled IB through VIII (although not in that order). 

Amended Main groups and transition groups are labeled lA through VIII and then IB through VIIB plus 0. 

This is not the periodic table supplied on the AP exam. The one in this book has family and period labels. Become familiar with these labels so that you can effectively use the unlabeled one. You may wish to add labels to the one supplied with the AP exam. 

Each square on this table represents a different element and contains three bits of information. The first is the element symbol. You should become familiar with the symbols of the commonly used elements. Secondly, the square fists the atomic number of the element, usually centered above the element. This integer represents the number of protons in the element s nucleus. The atomic number will always be a whole number. Thirdly, the square fists the elements mass, normally centered underneath the element symbol. This number is not a whole number because it is the weighted average (taking into consideration abundance) of all the masses of the naturally occurring isotopes of that element. The mass number can never be less than the atomic number. 

Elements bordering the stair-stepped line (B, Si, Ge, As, Sb, Te) are classified as metalloids. Metalloids have properties of both metals and nonmetals. Their unusual electrical properties make them valuable in the semiconductor and computer industry. 

The rest of the elements, to the right of the metalloids, are called nonmetals. Nonmetals have properties that are often the opposite of metals. Some are gases, are poor conductors of heat and electricity, are neither malleable nor ductile, and tend to gain electrons in their chemical reactions to form anions. 

Another way to group the elements on the periodic table is in terms of periods and groups (families). Periods are the horizontal rows, which have consecutive atomic numbers. The periods are numbered from 1 to 7. Elements in the same period do not have similar properties in terms of reactions. 

A FIGURE 2.13 The Periodic Table Main-Group and Transition Elements The elements in the periodic table fall into columns. The two columns at the left and the six columns at the right comprise the main-group elements. Each of these eight columns is a group or family. 

The properties of main-group elements can generally be predicted from their position in the periodic table. The properties of the elements in the middle of the table, known as transition elements, are less predictable. 

The group 1A elements, called the alkali metals, are all reactive metals. A marblesized piece of sodium explodes violently when dropped into water. Lithium, potassium, and rubidium are also alkali metals. 

The group 2A elements, called the alkaline earth metals, are also fairly reactive, although not quite as reactive as the alkali metals. Calcium, for example, reacts fairly vigorously when dropped into water but does not explode as dramatically as sodium. Other alkaline earth metals include magnesium (a conunon low-density structural metal), stfontium, and barium. 

For example, lithium, a metal with 3 electrons, tends to lose 1 electron, forming a 1-1- cation that has the same number of electrons (2) as helium. Chlorine, a nonmetal with 17 electrons, tends to gain 1 electron, forming a 1— anion that has the same number of electrons (18) as argon. 

The number of protons plus neutrons in an atom is termed the mass number. The number of protons (whieh also equals the number of eleetrons) is the atomie number. When elements are arranged in order of their atomie numbers and then aiuanged in rows, with a new row starting after eaeh noble gas, the seheme is termed the periodie table. A simplified version is shown in Table 3.2. 

Eleetronegativities inerease aeross a period to a maximum with Group VII, the halogens, for whieh reaetivity deereases from top to bottom of the table. Elements in Group 0 are unreaetive 

Chemieal equations are used to deseribe reaetions between eompounds. The formulae of the reaetants are written on the left-hand side of the equation and the formulae of the produets on the right. If a number of moleeules of one kind take part in the reaetion the number is written as a eoeffieient in front of the formulae. The two sides of the equation must balanee. 

To illustrate, both hydrogen and ehlorine have a valeney of one. Elemental hydrogen eonsists of two hydrogen atoms linked to form a moleeule of hydrogen written as H2. Elemental ehlorine eomprises moleeules of two atoms, CI2. One moleeule of hydrogen ean reaet with one moleeule of ehlorine to produee two moleeules of hydrogen ehloride  

Whereas some atoms have only one valency, others have several, e.g. sulphur has valencies of two, four and six and can form compounds as diverse as hydrogen sulphide, H2S (valency two), sulphur dioxide, SO2 (valency four) and sulphur hexafluoride, SF6 (valency six). Clearly some compounds comprise more than two different elements. Thus hydrogen, sulphur and oxygen can combine to produce sulphuric acid, H2SO4. From the structure it can be seen that hydrogen maintains its valency of one, oxygen two and sulphur is in a six valency state. 

The early nineteenth century saw a rapid advance in analytical chemistry in which many new elements were identified and attempts were made to classify them. J.W. Dobereiner found triads of elements such as Cl, Br, I and Li, Na, K that had similar chemical properties and noticed that the atomic weight of the middle element was close to the average of the other two. In 1869 Mendeleyev proposed the periodic law in which the elements arranged according to the magnitude of atomic weights show a periodic change of properties.  

List of Some of the More Important Common Elements 

Element Symbol Atomic Number Atomic Mass Significance 

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CH2CI-CO-CH3. Colourless lachrymatory liquid b.p. 119°C. Manufactured by treating propanone with bleaching powder or chlorine. It is used as a tear gas and is usually mixed with the more potent bromoacetone. chloro acids Complex chloroanions are formed by most elements of the periodic table by solution of oxides or chlorides in concentrated hydrochloric acid. Potassium salts are precipitated from solution when potassium chloride is added to a solution of the chloro acid, the free acids are generally unstable. 

The definitive reference series in inorganic chemistry although the complete periodic table is not covered. 

This missing synuuetry provided a great puzzle to theorists in the early part days of quantum mechanics. Taken together, ionization potentials of the first four elements in the periodic table indicate that wavefiinctions which assign two electrons to the same single-particle fiinctions such as... 

The most recent comprehensive text concentrating on the entire Periodic Table. Individual elements are also covered from time to time in monographs and reviews, e.g. in Progress in NMR Spectroscopy. 

Nuclei with spin about tliree-quarters of the periodic table, have a quadnipolar moment and as a... 

The group IV semiconductor materials are fourfold coordinated covalent solids from elements in column IV of tire periodic table. The elemental semiconductors are diamond, silicon and gennanium. They crystallize in tire diamond lattice. 

The usual acceptor and donor dopants for Al Ga As compounds are elements from groups II, IV and VI of the periodic table. Group II elements are acceptors and group VI elements are donors. Depending on the growth conditions. Si and Ge can be either donors or acceptor, i.e. amphoteric. This is of special interest in LEDs. 

Reference to the modern periodic table (p. (/)) shows that we have now completed the first three periods—the so-called short periods. But we should note that the n = 3 quantum level can still accommodate 10 more electrons. 

Note. The electronic configuratioa of any element can easily be obtained from the periodic table by adding up the numbers of electrons in the various quantum levels. We can express these in several ways, for example electronic configuration of nickel can be written as ls 2s 2p 3s 3d 4s. or more briefly ( neon core ) 3d 4s, or even more simply as 2. 8. 14. 2... 

Chemical properties and spectroscopic data support the view that in the elements rubidium to xenon, atomic numbers 37-54, the 5s, 4d 5p levels fill up. This is best seen by reference to the modern periodic table p. (i). Note that at the end of the fifth period the n = 4 quantum level contains 18 electrons but still has a vacant set of 4/ orbitals. 

The detailed electronic configurations for the elements atomic numbers 5 5-86 can be obtained from the periodic table and are shown below in Table 1.5. 

Chemical, physical and spectroscopic data all suggest a periodic table as shown on p. (/T. 

The periodic table also contains horizontal periods of elements, each period beginning with an element with an outermost electron in a previously empty quantum level and ending with a noble gas. Periods 1, 2 and 3 are called short periods, the remaining are long periods Periods 4 and 5 containing a series of transition elements whilst 6 and 7 contain both a transition and a rare earth senes,... 

When Mendeleef devised his periodic table the noble gases were unknown. Strictly, their properties indicate that they form a group beyond the halogens. Mendeleef had already used Group VIIl to describe his transitional triads and the noble gases were therefore placed in a new Group O. 

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