Group The elements in a vertical

Group. The elements in a vertical column of the periodic table. (2.4) Half-cell reactions. Oxidation and reduction reactions at the electrodes. (19.2) Half-life. The time required for the concentration of a reactant to decrease to half of its initial concentration. (13.3) Half reaction. A reaction that explicitly shows electrons involved in either oxidation or reduction. (4.4)... 

Group (femily) The elements in a vertical column of the periodic table. 

SECTION 2.5 The periodic table is an arrangement of the elements in order of increasing atomic number. Elements with similar properties are placed in vertical columns. The elements in a column are known as a group. The elements in a horizontal row are known as a period. The metaiilc elements (metals), which comprise the majority of the elements, dominate the left side and the middle of the table the nonmetalllc elements (nonmetals) are located on the upper right side. Many of the elements that lie along the line that separates metals from nonmetals are metalloids. 

The periodic table arranges the elements in a way that shows many of their properties and relationships to each other.The horizontal rows are called periods, and the vertical columns are called groups.The groups, numbered 1 through 18, are Hsted at the top of each column right underneath in parentheses are former Roman numeral group names I through Vlll that are sometimes still used. Each element is represented by a letter symbol, with the fuU name printed at the top. The atomic number, which is the number of proto ns in the nucleus, is written above each element. 

As more elements were discovered in the 19th century chemists started to note similarities in their properties. Early attempts to order the elements in a regular fashion were hampered by various difficulties, especially the fact (only later realized) that atomic masses do not increase regularly with atomic number. Mendeleev published the first satisfactory form of the periodic table in 1869, and although many details of layout have evolved since then, his basic idea has been retained, of ordering elements horizontally in periods so that they fall in vertical groups with similar chemical properties. Mendeleev was forced to leave some gaps for elements not yet discovered, and his ability to predict their properties vindicated his approach. 

The elements in a group have the same number of outer energy level electrons. They are located vertically on the periodic table. 

A convenient way to compactly represent such behavior is to use tables. The arrangement of the elements in a table based on the periodic law is called a periodic table. In a modem periodic table, such as the one inside the front cover of this book, elements with similar chemical properties are found in vertical columns called groups or families. 

Each element may be represented by a one- or two-letter symbol. In the mid-nineteenth century, a Russian chemist, Dmitri Mendeleev, saw that elements could be arranged according to repeating patterns of properties. Mendeleev s arrangement has evolved into the periodic table of the elements that you can see inside the back cover of this Handbook. The vertical columns of elements are called groups or families. The elements in a group have similar properties. Horizontal rows on the periodic table are called periods. When a new period starts, the elements tend to repeat the properties of the elements above them in the previous period. The value of Mendeleev s table was that it correctly predicted the properties of elements that had not yet been discovered. 

Suffice it to say that Dobereiner s research established the notion of triads as a powerful concept, which several other chemists were soon to take up with much effect. Indeed, Do-bereiner s triads, which would appear on the periodic table grouped in vertical columns, represented the first step in fitting the elements into a system that would account for their chemical properties and would reveal their physical relationships. 

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

Look at the periodic chart opposite.1 The elements in the same vertical columns have very similar properties. For example, all the elements in Group I are metals that react with water to produce hydrogen. This is because the electrons in all the elements in Group I are arranged around the nucleus in a similar pattern. 

Similarity between quantum systems, such as atoms and molecules, plays a very important role throughout chemistry. Probably the best example is the ubiquitously known periodic system of the elements. In this system, elements are arranged both horizontally and vertically in such a way that in both directions, elements have a high similarity to their neighbors. Another closely related idea is that of transferability. In chemistry, one speaks of transferability of an entity when its properties remain similar between different situations. An example is the transferability of the properties of a functional group between one molecule and another. The main motto of using similarity in chemistry is the assumption that similar molecules have similar properties. 

The matrix also includes vertical columns in which elements are arranged somewhat according to similarities between their chemical and physical properties and those properties of the elements located just above and below them in the column, or group. Thus, the three somewhat similar elements in a group might be thought of as a triad. ... 

This book uses the vertical structure for listing the elements in groups 13 through 18 between periods 2 and 5. Therefore, the elements included as metallics, metalloids, nonmetals, and so on are arranged in a different order (vertical) according to their atomic numbers rather than following the zigzag line on the periodic table. 

Figure 12.3 Vertical distributions of Group 1 elements (excluding H) and Group 2 elements in the North Pacific. Data sources Li (Stoffyn-Egli and Mackenzie, 1984), Na (Millero and Leung, 1976), K (Riley and Tongudai, 1967), Rb (Spencer ef a/., 1970), Cs (Spencer ef a/., 1970),...

---