Question

1. what is the difference between valency andvalence electrons


2. explain how on moving left to right in the periodic table the valency first increases and then decreases .explain with examples

Answer 1

Ans-1->The combining capacity of an atom is called its valency. Actually it can be defined as the number of electrons that an atom may lose (or) gain during a chemical reaction (or) the number of electrons shared. Ex: In water molecule H₂O (H - O – H)   Valency of Hydrogen is ‘ 1 ‘ (as it combines with Oxygen atom by  one single bond) and valence electrons in Hydrogen  = 1  Valency of Oxygen is ‘2’ (as it combines with two Hydrogen atoms by two bonds), but valence electrons in oxygen  = 6 The numbers of electrons in outermost shell (or) valency shell of an atom are called valency electrons. Based on valency electrons the group number of an atom can be found. Ex: Number of valence electrons in chlorine are 7 so it belongs to VIIA - group, but its valency is 1.   So, it is to be understood that some times valency is equal to valence electrons, but not all the time. A. ANS-2->Atomic size decreases on going along a period from left to right because the elctron enters into the same shell, therefore, attraction between nucleus and outermost electron increases and thus atomic size decreases. Valency first increases from 1 to 4 and then decreases from 4 to 0 along a period from left to right.

Answer 2

1.valence electrons are the electrons in the outermost shell of an element whereas valency electrons are the number of electrons that should be accepted or removed to attain the nearest noble gas configuration. It is the electrons in the outermost shell that usually contribute to form chemical bonds. In some atoms, the number of valence electrons is equal to the number of valency electrons.

I only know the 1st answer. thanks