Periodic Table of Elements

Transcription

1 Periodic Table of Elements A periodic table is a tabular display of elements organized by their atomic numbers, electron configurations, and chemical properties. LEARNING OBJECTIVES Explain how properties of elements vary within groups Describe arrangement of elements in the periodic table Explain how properties of elements vary across periods KEY POINTS A periodic table is a useful framework for analyzing chemical behavior. Such tables are widely used in chemistry and other sciences. The periodic table lists all the elements, with information about their atomic weights, chemical symbols, and atomic numbers. A group, or family, is a vertical column in the periodic table. Groups usually have more significant periodic trends than do periods and blocks. The vertical columns (groups) of the periodic table are arranged such that all its elements have the same number of valence electrons. All elements within a certain group thus share similar properties A period is a horizontal row in the periodic table. Elements in the same period show trends in atomic radius, ionization energy, electron affinity, and atomic numbers. KEY TERMS atomic number

2 The number, equal to the number of protons in an atom, that determines its chemical properties. Symbol: Z group A vertical column in the periodic table, which signifies the number of valence shell electrons in an element's atom. period A horizontal row in the periodic table, which signifies the total number of electron shells in an element's atom. atomic orbital The quantum mechanical behavior of an electron in an atom describing the probability of the electron's particular position and energy. ionization energy the amount of energy required to remove an electron from an atom or molecule in the gas phase electron affinity the amount of energy released when an electron is added to a neutral atom or molecule to form a negative ion Element Symbols The periodic table is structured as an 18 X 7 grid, positioned above a smaller double row of elements. The periodic table only lists chemical elements, and includes each isotope of each element within one cell. In the

3 typical periodic table, each element is listed by its element symbol and atomic number. For example, "H" denotes hydrogen, "Li" denotes lithium, and so on. Most elements are represented by the first letter or first two letters of their English name, but there are some exceptions. Two notable exceptions include silver and mercury. The symbol for silver is "Ag" from Latin argentum, which means "gray" or "shining." The symbol for mercury is "Hg" from the Latinized Greek hydrargyrum, which means "water-silver." Many periodic tables include the full name of element as well and color-code the elements based on their phase at room temperature (solid, liquid, or gas).

4 The periodic table The periodic table is a tabular display of all the chemical elements. The atoms are grouped in order of increasing atomic number.

5 The periodic table is a tabular display of the chemical elements. The elements are organized based on their atomic numbers, electron configurations, and recurring chemical properties. In the periodic table, elements are presented in order of increasing atomic number (the number of protons). The rows of the table are called periods; the columns of the s- (columns 1-2 and He), d- (columns 3-12), and p-blocks (columns 13-18, except He) are called groups. (The terminology of s-, p-, and d- blocks originate from the valence atomic orbitals the element's electrons occupy. ) Some groups have specific names, such as the halogens or the noble gases. Since, by definition, a periodic table incorporates recurring trends, any such table can be used to derive relationships between the properties of the elements and predict the properties of new, yet-to-be-discovered, or synthesized elements. As a result, the periodic table provides a useful framework for analyzing chemical behavior, and such tables are widely used in chemistry and other sciences.

6 Blocks in the Periodic Table A diagram of the periodic table, highlighting the different blocks

7 History of the Periodic Table Although precursors exist, Dmitri Mendeleev is generally credited with the publication, in 1869, of the first widely recognized periodic table. Mendeleev designed the table in such a way that recurring ("periodic") trends in the properties of the elements could be shown. Using the trends he observed, he even left gaps for those elements that he thought were "missing. " He even predicted the properties that he thought the missing elements would have when they were discovered. Many of these elements were indeed later discovered, and Mendeleev's predictions were proved to be correct. Rows and Periods The element symbol is always almost accompanied by other information such as atomic number and atomic weight. Atomic number describes the number of protons in one atom of that element. For example, an atom of oxygen contains 8 protons. Elements are listed in order of increasing atomic number from left to right. Each row of the periodic table is called a period and each column of the periodic table is called a group (or family).

8 Some groups have specific names like the halogens or noble gases. Elements within the same period or group have similar properties. Groups A group, or family, is a vertical column in the periodic table. Groups usually have more significant periodic trends than do periods and blocks, which are explained below. Modern quantum mechanical theories of atomic structure explain group trends by proposing that elements in the same group generally have the same electron configurations in their valence (or outermost, partially filled) shell. Consequently, elements in the same group tend to have shared chemistry and exhibit a clear trend in properties with increasing atomic number. However, in some parts of the periodic table, such as the d-block and the f-block, horizontal similarities can be as important as, or more pronounced than, vertical similarities. Periods A period is a horizontal row in the periodic table. Although groups generally have more significant periodic trends, there are regions where horizontal trends are more significant than vertical group trends, such as

9 in the f-block, where the lanthanides and actinides form two substantial horizontal series of elements. Elements in the same period show trends in atomic radius, ionization energy, and electron affinity. Atomic radius usually decreases from left to right across a period. This occurs because each successive element has an added proton and electron, which causes the electron to be drawn closer to the nucleus, decreasing the radius. The periodic table

10 Here is the complete periodic table with atomic numbers, groups, and periods. Each entry on the periodic table represents one element, and compounds are made up of several of these elements. Determining Chemical Properties using the Periodic Table Chemical properties of each element are determined by the element's electronic configuration, and particularly by its outermost valence electrons. An element's location in the periodic table is largely dependent on its electrons; the number of valence shell electrons determines its group, and the type of orbital in which the valence electrons lie in determines the element's block. In addition, the total number of electron shells an atom determines which period it belongs to. Because of its structure, the periodic table has become an extremely useful tool for assessing and predicting elemental and chemical trends.

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