# How to make a substance formula

Do you need to make a chemical formula, but you absolutely forgot fundamentals of school chemistry? Believe, you should not worry. Today more than 20 million chemical compounds are known, and, believe, nobody holds their formulas at himself in the head. It is enough to know the simple principle of their writing.

## It is required to you

• periodic table of Mendeleyev, table of solubility of salts

## Instruction

1. The problem of drawing up a chemical formula of substance comes down to creation of an electroneutral system. Therefore you will need to pick up some number of electrons for each element of connection so that it was counterbalanced. However before to make it, you should remember some theoretical bases. Any element of the periodic table of Mendeleyev has the valency (oxidation level), that is ability to give or accept a number of electrons, taking into account the valency, no more than eight electrons. Valency of each chemical element corresponds to number of group in the periodic table (the top line written by the Roman figures). It is worth noticing that all elements of the table of Mendeleyev can be divided into two classes conditionally: oxidizers and reducers. The first, as a rule, only take away electrons, the second – give.

2. For drawing up a chemical formula it is also necessary to know with what type of connections you deal. They can be divided into the following groups: 1. Binary; 2. Bases, salts, acids.

3. For drawing up a formula of binary connections you will need Mendeleyev's table, and for other groups – the table of solubility of salts. On the first place it is accepted to write metal or an element in formulas of binary connections with a smaller valency, on the second – nonmetal or an element with a bigger valency. Let's say it is necessary to make a tantalum oxide formula. Write down a number of designation of these elements and put down their valency: Ta5O6. Tantalum, respectively, is capable to give 3 electrons, and oxygen – to accept two, that is: Ta3+ O2-. Thus, for creation of a balanced system by cross-crosswise method (interchanging the position of indexes of chemical elements and rejecting their signs) you receive the following formula: Ta2O3.

4. For drawing up formulas of the bases, salts and acids it is necessary to use the table of solubility of salts. In its top line cations – the substances giving electrons, and in the left column – anions, that is the connections capable to accept electrons are specified. Using the table of solubility of salts, it is possible to receive the following formula for aluminum sulfate: Al3 + SO42-. Using the principle "a cross - crosswise", the final formula of substance will have an appearance: Аl2(SO4)3. As you can see, the algorithm of drawing up chemical formulas is very simple. It remains invariable for any other connections.

Author: «MirrorInfo» Dream Team