Nursing Entrance Exam

9.2.5 The Periodic Table The periodic table contains the known chemical elements displayed in a special tabular arrangement based on their electron configurations, atomic numbers, and recurring chemical properties. The first semblance of a periodic table was by Antoine Lavoisier in 1789. He published a list, or table, of the 33 chemical elements known at that time. He grouped the elements into earths, non-metals, gases, and metals. In the following century, several chemists began looking for a better classification method, which led to the periodic table we use today. Structure of the Periodic Table The standard periodic table is comprised of 18 columns and seven rows that contain the main chemical elements. Under this table is a smaller one – 15 columns by two rows. The periodic table can be broken down into four rectangular blocks: the P block is by the right, S block is left, D block is at the middle, and the F block is underneath that. The elements in the blocks are based on in which sub-shell the last electron resides. The chemical elements on the table are arranged in order of increasing atomic number, which refers to the number of protons of the element. The periodic table can be used to study the chemical behavior of chemical elements, which makes it a widely used tool in chemistry. The periodic table contains only chemical elements; mixtures, compounds, or small atomic particles of elements are not included. A new period begins when an element has a new electron shell with a first electron. Columns are based on the configuration of electrons of the atom. Elements that have an equal number of atoms in a specific sub-shell are listed under the same column. For example, selenium and oxygen both have four electrons in their outermost sub-shell and so are listed under the P column. Elements with similar properties are listed in the same group although some elements in the same period can also share similar properties. Since the elements grouped together have related properties, one can easily predict the property of an element if the properties of the surrounding elements are alreadyknown. Rows are Periods: The rows of the periodic table are called periods. Elements on a row have the same number of electron shells, or atomic orbitals. Elements on the first row have just one atomic orbital, elements on the second row have two, and so on. Columns are Groups: Columns in the periodic table are called groups. The columns in the D, P, and S blocks are called groups. Elements within a group have an equal number of electrons in their outermost electron shell. The electrons on the outer shell are called valence electrons and there are the electrons that combine with other elements in a chemical reaction. The periodic table contains natural and synthesized elements. The elements up to californium are naturally existing elements (94) while the rest were laboratory synthesized. To date, chemists are still working to produce elements beyond the present 118 th element, ununoctium. Of the 118 elements, 114 have been officially recognized by the International Union of Pure and Applied

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