Elements A First Look at the Periodic Table

Check The individual portions seem right 100 amu X 0.50 = 50 amu. The portions should be almost the same because the two isotopic abundances are almost the same. We rounded each portion to four significant figures because that is the number of significant figures in the abundance values. This is the correct atomic mass (to two decimal places), as shown in the list of elements inside front cover). 

An atom has a central nucleus, which contains positively charged protons and uncharged neutrons and is surrounded by negatively charged electrons. An atom is neutral because the number of electrons equals the number of protons. An atom is represented by the notation zX, in which Z is the atomic number (number of protons), A the mass number (sum of protons and neutrons), and X the atomic symbol. An element occurs naturally as a mixture of isotopes, atoms with the same number of protons but different numbers of neutrons. Each isotope has a mass relative to the mass standard. The atomic mass of an element is the average of its isotopic masses weighted according to their natural abundances and is determined by mass spectrometry. 

At the end of the 18 century, Lavoisier compiled a list of the 23 elements known at that time by 1870, 65 were known by 1925, 88 today, there are 114 and still counting These elements combine to form millions of compounds, so we clearly need some way to organize what we know about their behavior. By the mid-19 century, enormous amounts of information concerning reactions, properties, and atomic masses of the elements had been accumulated. Several researchers noted recurring, or periodic, patterns of behavior and proposed schemes to organize the elements according to some fundamental property. 

Each element has a box that contains its atomic number, atomic symbol, and atomic mass. The boxes lie in order of increasing atomic number (number of protons) as you move from left to right. 

At this point in the text, the clearest distinction among the elements is their classification as metals, nonmetals, or metalloids. The staircase line that runs from the top of Group 3A(13) to the bottom of Group 6A(16) in Period 6 is a dividing line for this classification. The metals (three shades of blue) appear in the large lower-left portion of the table. About three-quarters of the elements are metals, including many main-group elements and all the transition and inner 

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Isotopes and Atomic Masses Elements A First Look at the Periodic Table... 

Let us first take a brief look at the periodic table, which helps us to organize many properties of the elements, including their chemical reactions. 

Look at the periodic table. There is a darker stairstep line dividing it into right and left portions. The elements to the left of this line are called metals, whereas those to the right are called nonmetals, with the exception of the column of elements on the right-hand border of the table. These elements in the last column are neither metals nor non-metals but rather are called noble gases. Helium (He), the familiar gas used to fill up balloons, is the first of these noble gases. 

Look at the periodic table hanging on the wall of your classroom or the one inside the back cover of your textbook. Notice that the elements are numbered from 1 for hydrogen, 2 for helium, through 8 for oxygen, and on to numbers above 100 for the newest elements created in the laboratory. At first glance, it may seem that these numbers are just a way of coimting elements, but the numbers mean much more than that. Each number is the atomic number of that atom. The atomic number of an element is the number of protons in the nucleus of an atom of that element. It is the number of protons that determines the identity of an element, as well as many of its chemical and physical properties, as you will see later in the course. 

Iron as a transition element Why is iron a transition metal To understand this we need to look at the periodic table of elements, where iron occupies a central position in the first row of d block elements. The properties of these elements are transitional between the metallic behaviour of the s-block elements and the variable valency of the p-block. But the variable valency of the transition metals is entirely different to that of the p-block elements. Whereas the latter have valencies that increase in steps of... 

The periodic table of elements is divided into horizontal rows and vertical colunuis. Elements in a particular column have similar chemical behaviom. Looking at the periodic table, the metals are in Row 2 (lithium, beryllium), Row 3 (sodimn, magnesium, aluminium), Row 4 (potassium, K through to gallium, Ga), Row 5 (rubidimn through to tin), Row 6 (caesium to bismuth) and Row 7 (francium to actinium). There are two special series of metals from atomic number 58-71 and 89-103. The first are the rare earth metals and the second the radioactive metals (those beyond 92 do not occur naturalfy). Nos 90 and 92 occur naturally and are used for atomic power. The rest of the elements in the table ate non-metals. Some have some metal-like properties and are called metalloids, e.g. nos 5, 14, 32, 33, 51, 52, 84 and 85. 

There are 109 elements in existence, and more than 13 million compounds. Many of the elements are familiar to us. Examples include various metals such as iron, copper, aluminum, and lead. Also familiar are elements that are not metals (nonmetals). Examples of these are helium, hydrogen, oxygen, and iodine. For convenience, all elements have been assigned symbols. A symbol consists of one or two letters, the first a capital letter and the second, if used, a lower case letter. These letters are derived from either the English name or the Latin name of the element. For example, Al is the symbol for aluminum, and I is the symbol for iodine. In these two examples, the symbol is either the first letter or the first two letters of the English name. The symbol Fe represents iron and is derived from its Latin name ferrum. Other examples are Cu (from cuprum, the Latin word for copper), Na (from natrium, the Latin word for sodium), and Pb (for plumbum, the Latin word for lead). All 109 elements are listed in a table that chemists have developed, known as the periodic table. The periodic table contains the names and symbols of all the elements, as well as some numeric information. This numeric information will become important to us as our study of chemistry proceeds. However, for the present discussion, let us take a look at the periodic table and especially notice the names and symbols. An example of a periodic table is presented in Figure 1.2. 

Specific interest in the periodic table and the elements has produced a number of recent books. One of the first serious examinations of the history of the elements was done by May Elvira Weeks. Discovery of the Elements (1968), an updated version with material from Henry M. Leicester, can still be found in libraries. Richard Morris s The Last Sorcerers The Path from Alchemy to the Periodic Table (2003) is an excellent book, while Paul Strathern s Mendeleyev s Dream (2000) is a nontechnical look at the hunt for order among the elements that reads almost like a novel. More technical material on matter theory can be found in Antio Clericuzio, Elements, Principles, and Corpuscles A Study of Atomism and Chemistry in the Seventeenth Century (2000) David M. Knight, Atoms and Elements. A Study of Theories of Matter in England in the Nineteenth Century (1967) and Mary Jo Nye, From Chemical Philosophy to Theoretical Chemistry Dynamics of Matter and Dynamics of Disciplines 1800-1950 (1993). 

This part uses the element hydrogen as a guide to the concepts of the periodic table. This small and simple atom serves as the first step in your journey through the periodic table. We present all of the elements from the alkali and alkaline earth metals, to the main group elements, and even the span of transition metals that connect one side of the periodic table to the other. You also get a good look at the mysterious, rare, and exotic lanthanide and actinide elements. 

Before looking more closely at the periodic table, we briefly explore two theories that explain why the properties of elements recur in a periodic fashion. The first theory is called the Bohr model for the atom, after Bohr (1885-1962), and it links the macroscopic observation-that certain elements have similar properties that recur-to the microscopic reason-that the atoms comprising the elements have similarities that recur. 

The modern periodic table first appeared as a page for a chemistry textbook, written by a teacher who thought his students needed an easy way to look at the elements. The shape of the table made it world-famous, for all the reasons mentioned. The carefully stacked rows and columns made a simple list into a useful tool and a snapshot of how matter is organized on Earth and throughout the universe. 

First things first, you need to understand the nature of elements, and their oxidation states (number of bonds). Every single element is capable of forming chemical bonds with other elements (with the exception of a few noble gases ). The oxidation states are what determines how many bonds a particular element can form, and to what other elements. When elements combine, they form chemical compounds. All of the atoms within a chemical compound show specific oxidation states. Oxidation states are not really states, but definitions of bonding, which are dictated by each individual element. Each element can form any where from either 0 to 7 bonds. These numbers represent the number of bonds the element can form (look at a modem periodic table, such that included in the Merck Index —the oxidations states are written in the upper left comer of each element). These numbers clearly indicate the number of bonds each element is capable of forming. 

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