What is valency in chemistry?

Answer 1

In chemistry, valence usually refers to the valence electrons (VE), which are the outer electrons of an atom, ion, or compound. The most valence electrons any single atom can have is 8, allowing for a full octet. (Note: This "octet rule" generally does NOT apply to transition metals, lanthanides, or actinides because of their d and f energy sub-levels.) The valence electrons determine many of the characteristics of the atom, especially bond types and reactivity. For example, sodium (Na) has the atomic number 11. Its electron configuration is 1s2 2s2 2p6 3s1 (11 electrons). There is only one electron in sodium's outer shell, meaning there is only on evalence electron. The same goes for the remaining alkali metals (H, Li, K, etc.). The number of valence electrons can easily be determined by examining the Periodic Table of the elements. Group 1A (alkali) have one VE, Group 2A (alkaline) have two VE, Group 3A (aka group 13) have 3, 4A has 4... etc. Remember, this only applies to atoms with s and p outer shells. Because having eight valence electrons is desirable/ most stable, Na has the ability to give away its single valence electron to be more like neon (Ne), which has only 10 electrons. For this reason Na will give its electron to another atom in need, such as chlorine (Cl), with only 7 VE. Through this "ionic bond", both the Na and the Cl obtain a full octet.

Answer 2

Valency electrons and the valence of an atom are different things. Valency electrons are the electrons in an atom's outer shell, while the valence of an atom determines how many atoms of an element a particular atom can combine with.

Answer 3

valency is the number of free electrons in the last shell