Representative elements, periodic table

Period (in the periodic table) Periodic table Representative element Transition element (or metal)... 

Figure 1.1 The position of carbon in the periodic table. Other elements commonly found in organic compounds are shown in the colors typically used to represent them.

The modern periodic table represents a pinnacle of the achievement of many nineteenth- and twentieth-century chemists, and is a clear visual expression of our understanding of the structure of the atom. It is not only beautiful, however - it is also supremely useful. It offers a simple key to predicting a wealth of physical and chemical data about the elements and their compounds. It is possible to predict the properties and behavior (biogeochemically, as well as chemically) of hundreds of compounds, from a knowledge of a few. It is the key to understanding modern chemistry. 

The two periods at the bottom of the periodic table represent two special groups that fall between the s and d blocks. The period beginning with lanthanum (La) is called the lanthanides. The next period beginning with actinium (Ac) is the actinides. Elements in these two periods form the f-block. 

At this moment more than 100 kinds of atoms are known. The exact number is open to debate because the atoms with an atomic number of 85 or higher are no longer stable, i.e. these atoms are radioactive. When an atom is radioactive it emits certain kinds of radiation which can for example contain protons, electrons and neutrons. Every kind of atom represent a kind of element, all of which can be arranged in a table according to the increasing atomic numbers and the similarities in properties. This table is called the periodic table of elements, abbreviated PT. Similarities in properties are mainly caused by the same number of atoms in the outermost shell. 

The atomic mass that is given in the periodic table represents the average mass of all the naturally occurring isotopes of the element. It takes into account their isotopic abundances. 

The periodic table. The elements in the A groups are the representative elements. The elements shown in pink are called transition metals. The dark line approximately separates the nonmetals from the metals. The elements that have both metallic and nonmetallic properties (semimetals) are shaded in blue. 

The atomic mass unit (amu), which is represented with the symbol u, is based on a particular isotope of carbon, called carbon-12. Carbon-12 is considered to have a mass of exactly 12 u, and all of the other elemental isotopes are measured relative to that isotope. The atomic masses, shown on the periodic table, represent a weighted average of the masses of the naturally occurring isotopes of each element. For example, some periodic tables show an atomic mass of 1.00794 u for hydrogen, despite the fact that no particular isotope of hydrogen has a mass number equal to that value. 

It is often useful to refer to whole blocks of elements on the periodic table. The elements in groups 1, 2, and 13 through 18 (the A groups) are sometimes called the representative elements. They are also called the main-group elements. The elements in groups 3 through 12 (the B groups) are often called the transition metals. The 28 elements at the bottom of the table are called inner transition metals. 

The mass in grams of one mole of substance is called molar mass. Each element has its own unique molar mass. For example, carbon s molar mass is 12.011 g/mol, and magnesium s molar mass is 24.3050 g/mol. To see why these elements have different molar masses, we need to remember that the atoms of different elements contain different numbers of protons, neutrons, and electrons, so they have different masses. The atomic masses given in the periodic table represent the different weighted average masses of the naturally occurring atoms of each element. 

Identify A period 3 representative element is part of the rough material on the side of a match box used for lighting matches. Table 6.10 shows the ionization energies for this element. Use the information in the table to infer the identity of the element. Explain. 

Elements above lead (atomic numbers 83 and above) on the Periodic Table are radioactive (see Figure 9.2). Other elements may have one or more radioactive isotopes. Some elements occur naturally, while others are manmade. Each symbol on the Periodic Table represents one atom of that element. An atom is made up of a nucleus with varying numbers of electrons in orbits circling around the nucleus (see Figure 9.3). Located inside the nucleus are protons and neutrons. Protons in the nucleus of an atom represent the atomic number of that element. Neutron numbers may vary within the same type of element or from one element to another, but the number of protons must stay the same. The atom is the smallest part of an element that normally exists so any particle of an element that is smaller than an atom is commonly referred to as a subatomic particle. 

Figure 2.12 I The data from Figure 2.11 are presented here in a different form. The shading of the boxes in the periodic table represents the density of each element darker shading indicates higher density. The general trends in density are apparent as you look across a row or down a column.

Dmitri Mendeleev devised the first periodic table of elements, arranged by repetitions he recognized in the properties of elements. The current periodic table is organized in sequence of increasing atomic number. Elements in the same vertical column or group have similar properties. In columns 1, 2, and 13-18, representative elements extend above the rest. The elements found in columns 3-12 are transition eiements. Elements 58-71 and 90-103 are inner transition elements. 

The inner electron configuration for any element is the electron configuration of the noble gas that immediately precedes that element in the periodic table. Represent the inner configuration with the S5nnbol for the noble gas in brackets. 

FIGURE 2.9 Pie Periodic Table Each element is represented by its symbol and atomic number. Elements in the same column have similar properties. 

Le Poidevin makes special mention of the periodic system and of Mendeleev s prediction of new elements. He sets out to discover why Mendeleev was so confident that the elements he predicted actually existed. Le Poidevin claims that this is not a question about Mendeleev s confidence in the periodic law but rather about an implicit conceptual move. If one grants that the gaps in the periodic table represented genuine possibilities, elements that could exist, why did Mendeleev assume that the possibilities would actually be realized ... 

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. 

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