From the word "valence" many students studying chemistry in the 8th grade fall into hibernation.  Not much time is devoted to this issue in the school course of chemistry, although valence is one of the basic concepts in this  science . It is very important to thoroughly understand  what is valence , how it is defined and what significance it has. By understanding this and learning how to write formulas and determine the valence of elements, you will greatly facilitate your study of chemistry. Let's get started.

What is valence? There is nothing wrong with this phenomenon.

Valence is the ability of an atom to form chemical bonds. Also learn more about manganese valence electrons. 

Do you know that there are simple substances, consisting of atoms of the same type, and complex substances, consisting of atoms of different elements? So, in order for atoms to somehow connect with each other, they must bind, connect. And they are connected through a  chemical bond . Some atoms can form only one bond, they do not have the ability to do more. Other atoms are much more powerful, they can form several bonds in order to hold on to the environment more tightly. Imagine that you only have one friend. Such a reliable, faithful friend who is with you through fire and water. You always go with him. This means that you have  a  valencyI (attention! This is not read "first valency", but "valency one"!). Now imagine that you have three true friends. You always hold on to them and are firmly convinced that they are with you every minute. So you have valency III. In the first case, you formed one strong connection, and in the second - three. That's all valency.

Any teacher and tutor in chemistry will tell you that there are elements with a constant valence and elements whose valency can be different.

And, oddly enough, they will be right. If we return to the examples with friends, then it will look like this. Someone is friends with one person all his life (he always has valency I), someone is friends with three all his life (valency III). And someone is sometimes friends with one, sometimes with three, and sometimes - even with five! Have you met such people in your life? So among the chemical elements there are those that sometimes have valency I, sometimes valence III or even V. I should upset you a little:  elements with constant valency will have to be memorized . We also remember forever that valence is indicated by Roman numerals (it happened, just put up with it. The valency is indicated OVER the element in the formula). So, by heart, you need to learn that:

·  Metals of the main subgroups of the first group  always have valency I. These are the elements Li, Na, K, Rb, Cs, Fr.

· Metals of the main subgroup of the second group always have valency II. These are the elements Be, Mg, Ca, Sr, Ba, Ra.

Hydrogen always has valency I.

· Oxygen always has valency II.

· Elements Al and B (the main group of the third subgroup) always have valency III.

· Elements of the main subgroup of the seventh group more often (but not always!) Have a valence I. These are the elements F, Cl, Br, I, At. By the way, these elements are called "halogens" and be on your guard: halogens like to play a joke and sometimes have a different valency. In school chemistry, they are usually presented as monovalent, but this is coquetry, because halogens are naughty.

Now let's move on to elements with a non-constant valence. These are hooligans who like to guess riddles and play pranks on beginners. They show particular cunning during the Unified State Examination in Chemistry and even the Unified State Examination in Chemistry, confusing poor schoolchildren. So, remember these fickle-valence thugs in the face:

C (carbon), N (nitrogen), P (phosphorus), S (sulphur), Cr (chromium), Fe (iron), Cu (copper).

Of course, there are many more elements in the periodic table. But less than half of them are used in a school chemistry textbook. The fact is that in the fourth period of the table, the so-called d-elements with a complex structure and tricky properties appear, which schoolchildren are not supposed to be told about. Yes, and very well, there is nothing to hammer in your head.

I hope you understood the concept of "valence" after all. Next time we will practice in determining the valency of the elements, if there is a formula, and the correct formulation of the formulas of substances, if we know the valency.