Valence
So, we are familiar with the electronic configuration of the atom and ions. The world would be too simple if it were enough for us to understand the structure of the interaction of atoms. In fact, everything turns out to be more complicated, so there is nothing left but delve into the chemistry of the process. Scientists have not yet given us a simple description of why certain atoms add up into molecules and the only possibility for today is exclusively knowledge about existing substances. Base existing chemical compounds are stored in the IUPAC database.Stable configuration
A common electron cloud in the compound creates for atoms the illusion of a stable electronic configuration - configuration, in which the external energy levels of each of the atoms are filled. Using the example of a water molecule H2O - the electronic configuration of hydrogen 1s1 and the electronic configuration of oxygen - 1s22s22p4, for oxygen, stable configurations will be 1s22s22p6 and 1s22s2, but in practice the electronic configuration O4+ was not noticed, perhaps because it is quite difficult to tear off four electrons. Therefore, the nearest stable one will be O2-. For hydrogen, it is quite easy to take away and add an electron, so both configurations 1s0 and 1s2 are possible for it, therefore its stable states in the compound are H+ and H-.
Question 1. Which stable configuration is easiest for chlorine to adopt?
Which way will change the electronic configuration of hydrogen and oxygen in the compound H2O? Both hydrogen atoms will have to assume the same states, because if they accept the opposite, they will connect with each other and, having assumed a stable position, will cease to react with anyone. It is easier for oxygen to accept two electrons than to give up four - simply because two are less than four. Based on this, oxygen, most likely, it will take the configuration O2-, and hydrogen H+, as a result of their connection, a neutral compound is formed - a molecule that does not have a charge H2O.
Question 2. What is the oxidation state of oxygen in the compound H2O?
Number of links
In the compound of a water molecule, oxygen separates an electron cloud with two hydrogen atoms. In the molecule model we depict such sharing using lines, for example H-O-H - here two lines are connected with oxygen, one for hydrogen. In the case of a 3D model, the atom has the shape of a sphere, and the connections have the shape of tubes between them. Quantity such connections are called valence.
The connection is not always single, in some cases it is double or triple - such connections sum up its number to the valence. For example, nitrogen, which has an electronic configuration of 1s2 2s2 2p3, forms a nitrogen molecule N2, in which one atom has an oxidation state of +3, the other -3, together they form an electroneutral molecule and each of them has a triple bond. In this case, two atoms are connected, but the amount of there are three connections, the valence will be equal to three.
Often in tests there is a question, what is the degree of nitrogen oxidation in the molecule N2. The correct answer is zero. The reason is that there is no displacement of the electron cloud. In compounds of simple substances (formed by one atom) , the electron cloud is evenly distributed, which makes it impossible to say that one atom has a positive, and the other has a negative charge.
In simple substances, the degree of oxidation of atoms is zero: H2, N2, F2, O3 and so on.
Determination of valence, according to IUPAC:
The maximum number of univalent atoms (originally hydrogen or chlorine atoms) that may combine with an atom of the element under consideration, or with a fragment, or for which an atom of this element can be substituted.
Valence is the maximum number of monovalent atoms (initially hydrogen or chlorine) that can be attached to the atom in question, parts of the molecule [... or what the atom of this element can be replaced with].
So, I have analyzed the general rule for determining the valence of an atom in a molecule, then the main ones will be described rules that are used to determine the valence of an element.
Question 3. What is the degree of oxidation of nitrogen in compound N2?
How to determine the degree of oxidation
In the periodic table, the elements are grouped, among other things, according to the degrees of oxidation manifested. Below are the rules, which can be used when calculating the degree of oxidation, they will free you from the need to remember the degree of oxidation all elements.
Rule I
In the periodic table, the elements of the first group (first column) in the compounds exhibit oxidation states +1, the elements of the second groups — +2, elements IIIA — +3. Elements of groups older than the third - even groups exhibit even, odd - odd, for both - not older than their group, so for IVA (14) - +2,+4; for VIA (16) - +2,+4,+6; for VA (15) - +3,+5 ( there is an exception here, no +1); for VIIA (17) - +1,+3,+5,+7;
Rule II
Elements to remember: Feconi (Fe, Co, Ni) exhibit oxidation states of +2 and +3. Cu and Hg are +1 and +2
Rule III
Chromium and manganese can manifest themselves as metals and as non-metals: Cr in the case of metallic properties - +2, +3, non-metallic - +6. Manganese - +2, +3 in the case of metallic properties +4,+6,+7 in the case of non-metallic manifestations.
