The Periodic Table
Section 1: Understanding The Periodic Table
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The periodic table is a table of chemical elements arranged in order of their relative atomic numbers.
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The vertical columns are called ‘groups’ and the horizontal rows are called ‘periods’.
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Elements in the same group have the same number of electrons in their outermost shell and hence, have similar chemical properties.
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Elements in the same period have the same number of energy levels or electron shells.
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The atomic number on the periodic table represents the number of protons an atom of that element has. It is also called the proton number.
Section 2: The Groups of The Periodic Table
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Group 1 elements, the alkali metals, are very reactive metals.
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Group 2 elements, the alkaline earth metals, are reactive but less so than Group 1.
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Group 7 elements are the halogens, which are very reactive non-metals.
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Group 8 elements (Group 0 according to UK labelling) are the noble gases, which are very unreactive.
Section 3: Some Special Groupings
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Transition metals are found in the middle of the periodic table, between Group 2 and Group 3.
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Lanthanides and actinides are special groups of metals located at the bottom of the Periodic Table.
Section 4: Understanding Patterns in the Periodic Table
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As you move down a group, the elements become more metallic and reactivity increases (for metals) and decreases (for non-metals).
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As you move across a period to the right, elements become less metallic and the reactivity of metals decreases and reactivity of non-metals increases.
Section 5: Predicting Element Properties
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By understanding an element’s position on the periodic table, you can predict its physical and chemical properties:
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Metals (left and centre) are often solid at room temperature, good conductors of heat and electricity, and tend to lose electrons in chemical reactions.
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Non-metals (right) are often gases or brittle solids at room temperature, poor conductors of heat and electricity, and tend to gain electrons in chemical reactions.
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The number of outer electrons (also known as Valence electrons) determines how that element will react.
Section 6: Periodic Trends
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Atomic radius decreases across a period from left to right, and increases down a group.
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Ionic radius also follows the same trend as the atomic radius.
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Ionization energy (the energy required to remove an electron from an atom) increases from left to right across a period and decreases down a group.
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Electronegativity (a measure of the ability of an atom to attract electrons) too increases from left to right across a period, and decreases down a group.