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Valence Shell and Valence Electron, Basics of Valency _ Tutorvista

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  8/25/2014Valence Shell and Valence Electron, Basics of Valency | Tutorvista.com Basics of Valency  0  In this page we are going to discuss about structure of the atom  cobcept . The outermost shell of anatom is called its Valence shell . It is the decisive shell during a chemical reaction. The electrons of only this outermost shellare involved during chemical combinations; electrons are either given out from the outermost shell, or accepted into theoutermost shell, or shared with the electrons in the outermost shell of another element.  Example: K L MNa - 11 - 2 8 1Valence shell - MValence electrons - 1Core electrons - 2 + 8 = 10 Significance of Valence Electrons   Valence electrons of an atom are responsible for chemical reactions as they take part in them.Elements having same number of valence electrons in their atoms possess similar chemical properties. All alkali metalshave one valence electron in their atom. Thus, their chemical properties are similar.   AlkaliMetal . AtomicNumber Electronicconfiguration Number of ValenceElectrons  Lithium (Li) 3 2,1 1 Sodium (Na) 11 2,8,1 1 Potassium (K) 19 2,8,8,1 1   The number of the valence shell in an atom determines its position in the Periodic Table i.e. the period to which theelement belongs.Elements having 1, 2 or 3 electrons in the valence shell are metals. Exception is H and He. Elements having 4 to 7electrons in their valence shell are non-metals.   Examples :   Ex 1 : The electronic configurations of some of the elements are detailed below. How many valence and core electrons dothefollowing  8/25/2014Valence Shell and Valence Electron, Basics of Valency | Tutorvista.com have?(a) Al : 2, 8, 3(b) Mg: 2, 8, 2(c) Cl : 2, 8, 7(d) Ca : 2, 8, 8, 2 Solution : (a) Valence electrons = 3; core electrons = 10(b) Valence electrons = 2; core electrons = 10(c) Valence electrons =7; core electrons = 10(d) Valence electrons = 2; core electrons = 18 Ex 2 : Classify the following elements as metals or non-metals based on valence electrons: Solution : A - 2, 8, 2 - It is a metal as it has 2 valence electronsB - 2, 8, 6 - It is a non-metal as it has 6 valence electronsC - 2,6 - It is a non-metal as it has 6 valence electrons Ex 3:  Determine the period to which sodium (Na - 11) belongs. Solution:  Na - 11; 2, 8, 1Number of the valence shell - 3Therefore, sodium is placed in period 3 of the periodic table. Ex 4: Determine the period to which calcium (Ca - 20) belongs.  Solution :  Ca - 20; 2, 8, 8, 2Number of the valence shell - 4Therefore, sodium belongs to period 4 of the periodic table. Valency Valency is the combining capacity of an element. It is the number of electrons in an atom that actually take part in bondformation. For example, carbon atom with an atomic number 6 has 4 valence electrons.K LC 6  2 4Carbon atom is capable of forming 4 bonds. Hence its valency is four.   Calculation of Valency The number of valence electrons is the valency of the element.The valency of an element can also be calculated by finding the number of electrons required to complete octet (8)i.e., 8 - Number of valence electrons = Valency. Examples :Ex 1: Determine the valency of oxygen (O - 8). Solution : 0 - 8 : 2, 6Valency = 8 - Number of valence electrons= 8 - 6= 2 Ex 2 : Calculate number of valence electrons, the valency and valence shell of an atom whose atomic number is 17. Solution :   Electron configuration:   KLM287   Number of valence electrons = 7Valency = 8 - 7 = 1Valence shell = M  8/25/2014Valence Shell and Valence Electron, Basics of Valency | Tutorvista.com
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