What is the valence of aluminum

Valency of aluminum (Al), formulas and examples

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Aluminum is a silvery-white light metal. It is easily drawn into wire and rolled into thin sheets. Crystallizes in a face-centered cubic lattice. It has high electrical conductivity and thermal conductivity. The melting and boiling points are 660oC and -2500oC, respectively.

At room temperature, aluminum does not change in air, but only because its surface is covered with a thin film of oxide, which has a very strong protective effect.

Valency of aluminum in compounds

Aluminum is the thirteenth element of the Periodic Table D.I. Mendeleev. He is in the third period in group IIIA. The nucleus of an aluminum atom contains 13 protons and 14 neutrons (mass number 27). An aluminum atom has three energy levels containing 13 electrons (Fig. 1).

Rice. 1. Structure of the aluminum atom.

The electronic formula of the aluminum atom in the ground state is as follows:

1s22s22p63s23p1.

And the energy diagram (constructed only for electrons of the outer energy level, which are otherwise called valence):

Since in the third energy layer, in addition to the 3s sublevel, there is also a 3p sublevel, two orbitals of which are not occupied by electrons, a pair of electrons of the 3s sublevel is vaporized and one of them occupies the vacant orbital of the 3p sublevel. This means that the aluminum atom is characterized by the presence of an excited state:

The presence of three unpaired electrons indicates that aluminum exhibits valency III in its compounds (AlIII2O3, AlIII(OH)3, AlIIICl3, etc.). The valence of aluminum is constant.

Examples of problem solving

Source: http://ru.solverbook.com/spravochnik/ximiya/valentnost/valentnost-alyuminiya/

Valency of chemical elements (Table)

The valence of chemical elements is the ability of chemical atoms. elements form a certain number of chemical bonds. It takes values ​​from 1 to 8 and cannot be equal to 0. It is determined by the number of electrons of an atom spent on the formation of a chemical. bonds with another atom. Valence is a real value. Indicated by Roman numerals (I ,II, III, IV, V, VI, VII, VIII).

How can you determine valence in compounds:

— The valency of hydrogen (H) is always constant 1. Hence, in the compound H2O, the valency of O is 2.

— The valency of oxygen (O) is always constant 2. Hence, in the CO2 compound, the valency C is equal to 4.

— The highest valency is always equal to the group number.

- The lowest valency is equal to the difference between the number 8 (the number of groups in the Periodic Table) and the number of the group in which the element is located.

— For metals in subgroups A of the periodic table, valency = group number.

— Nonmetals usually have two valences: higher and lower.

The valence of chemical elements can be constant or variable. Constant mainly for metals of the main subgroups, variable for non-metals and metals of secondary subgroups.

Table of valency of chemical elements

Source: https://infotables.ru/khimiya/1071-valentnost-khimicheskikh-elementov

Valence. Determination of valence. Elements with constant valency

Valency is the ability of an atom of a given element to form a certain number of chemical bonds.

Figuratively speaking, valence is the number of “hands” with which an atom clings to other atoms. Naturally, atoms do not have any “hands”; their role is played by the so-called. valence electrons.

We can say it differently: valency is the ability of an atom of a given element to attach a certain number of other atoms.

The following principles must be clearly understood:

There are elements with constant valence (of which there are relatively few) and elements with variable valence (of which the majority)

Elements with constant valence must be remembered:

The remaining elements may exhibit different valencies.

The highest valence of an element in most cases coincides with the number of the group in which the element is located

For example, manganese is in group VII (side subgroup), the highest valence of Mn is seven. Silicon is located in group IV (main subgroup), its highest valency is four.

It should be remembered, however, that the highest valence is not always the only possible one. For example, the highest valence of chlorine is seven (make sure of this!), but compounds in which this element exhibits valences VI, V, IV, III, II, I are known.

It is important to remember a few exceptions : the maximum (and only) valence of fluorine is I (and not VII), oxygen - II (and not VI), nitrogen - IV (the ability of nitrogen to exhibit valency V is a popular myth that is found even in some school textbooks) .

Valency and oxidation state are not identical concepts

These concepts are quite close, but they should not be confused! The oxidation state has a sign (+ or -), the valence does not; the oxidation state of an element in a substance can be zero, the valency is zero only if we are dealing with an isolated atom; the numerical value of the oxidation state may NOT coincide with the valence. For example, the valency of nitrogen in N2 is III, and the oxidation state = 0. The valence of carbon in formic acid is = IV, and the oxidation state = +2.

If the valence of one of the elements in a binary compound is known, the valence of the other can be found

This is done very simply. Remember the formal rule: the product of the number of atoms of the first element in a molecule and its valency must be equal to a similar product for the second element .

In AxBy compound: valence (A) • x = valence (B) • y

Example 1. Find the valencies of all elements in the compound NH3.

Solution. We know the valence of hydrogen - it is constant and equal to I. We multiply the valence of H by the number of hydrogen atoms in the ammonia molecule: 1 • 3 = 3. Therefore, for nitrogen, the product of 1 (the number of atoms N) by X (the valence of nitrogen) should also be equal to 3 It is obvious that X = 3. Answer: N(III), H(I).

Example 2. Find the valencies of all elements in the Cl2O5 molecule.

Solution. Oxygen has a constant valency (II); the molecule of this oxide contains five oxygen atoms and two chlorine atoms. Let the valency of chlorine = X. We make up the equation: 5 • 2 = 2 • X. Obviously, X = 5. Answer: Cl(V), O(II).

Example 3. Find the valency of chlorine in the SCl2 molecule if it is known that the valency of sulfur is II.

Solution. If the authors of the problem had not told us the valence of sulfur, it would have been impossible to solve it. Both S and Cl are elements with variable valency. Taking into account additional information, the solution is constructed according to the scheme of examples 1 and 2. Answer: Cl(I).

In examples 1 - 3, we determined valency using the formula; now let's try to do the reverse procedure.

Example 4. Write a formula for the compound of calcium and hydrogen.

Solution. The valences of calcium and hydrogen are known - II and I, respectively. Let the formula of the desired compound be CaxHy. We again compose the well-known equation: 2 • x = 1 • y. As one of the solutions to this equation, we can take x = 1, y = 2. Answer: CaH2.

“Why exactly CaH2? - you ask. “After all, the variants Ca2H4 and Ca4H8 and even Ca10H20 do not contradict our rule!”

The answer is simple: take the minimum possible values ​​of x and y. In the example given, these minimum (natural!) values ​​are exactly 1 and 2.

“So compounds like N2O4 or C6H6 are impossible? - you ask. “Should these formulas be replaced with NO2 and CH?”

No, they are possible. Moreover, N2O4 and NO2 are completely different substances. But the formula CH does not correspond to any real stable substance at all (unlike C6H6).

Despite all that has been said, in most cases you can follow the rule: take the smallest index values.

Example 5. Write a formula for the compound of sulfur with fluorine, if it is known that the valency of sulfur is six.

Solution. Let the formula of the compound be SxFy. The valence of sulfur is given (VI), the valency of fluorine is constant (I). We formulate the equation again: 6 • x = 1 • y. It is easy to understand that the smallest possible values ​​for the variables are 1 and 6. Answer: SF6.

Here, in fact, are all the main points.

Now check yourself! I suggest you take a short test on the topic “Valence” .

Do you want to know why the “classical” definition of valency often doesn’t “work”? Why is the valence of iron in FeO not equal to two? Why is the concept of “coordination number” used to describe complex substances?

See the continuation of this article →

Source: http://www.repetitor2000.ru/valentnost_01.html