In this page we are going to discuss about structure of the atom cobcept . The outermost shell of an atom is called its Valence shell. It is the decisive shell during a chemical reaction. The electrons of only this outermost shell are involved during chemical combinations; electrons are either given out from the outermost shell, or accepted into the outermost shell, or shared with the electrons in the outermost shell of another element.
|Alkali Metal .||Atomic Number||Electronic configuration||Number of Valence Electrons|
Ex 1 : The electronic configurations of some of the elements are detailed below. How many valence and core electrons do the
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.
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.
Ex 1: Determine the valency of oxygen (O - 8).
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.
Number of valence electrons = 7Valency = 8 - 7 = 1Valence shell = M