All variety of existing substances is due to a combination of different kinds of atoms.It so happened that these kinds of atoms - little more than a hundred today.But they - the guys quite capricious, and combined with each other not by the rules of combinatorics, and in accordance with the laws of chemistry.Still, the number of agents is enormous, it is growing.But the number of known chemical elements almost not increased.Each one is unique and has its own "portrait".And the main feature of every element - the atomic mass.
unit of weight - a very small number.None of the existing kinds of atoms is ideally suited as a candidate for being a unit of weight (but the closest was a light hydrogen).As a result, researchers decided to take a number of convenient payments - one-twelfth of the absolute mass of an element such as carbon.It turned out, this number is very well expressed by the ratio in which atoms of the elements are to each other.So the atomic mass unit has been recognized for a number in a very small degree, this is a small figure "ten to the minus twenty-seventh degree."
It is clear that use of such a number is uncomfortable.You understand that the calculations everywhere carry the minus twenty-seventh degree not from the hand, and as a result of the same may be inconvenient, cumbersome.What to do?Use this unit as the relative atomic mass of the element.What is it?Everything is done very simply - taken an absolute atomic mass (number of extremely uncomfortable, almost the same level of negative), is divided into our one-twelfth the mass of carbon.So what?That's right, much reduced and it turns out it is a decent number.For example, the oxygen atom sixteen, fourteen - nitrogen.Carbon, logically, would have a mass of twelve.And the atomic weight of hydrogen - one, but not exactly one that proves that not all the hydrogen has been taken for the calculations, although the numbers to its mass is very close.
So why the relative atomic mass of each element - the number is not quite beautiful, non-integer?The fact is that the elements, though being the kinds of atoms within a species can afford a "diversity."Some of them are unstable, simply put, a very easy to spontaneously break.But for a while there, so they can not be ignored.Often and stable form of the elements generally includes subtypes with different atomic mass.They are called isotopes.That translated means that they take a cell known to every schoolchild table - yes, you guessed it right, the periodic table.
But is the atomic mass of the element makes the element?Not at all, it is characterized by an element of a much more fundamental number of protons in the nucleus.Here it can be fractional and indicates a positive charge of the nucleus.The "quiet" of the atom electrons as much as the protons in the nucleus, and therefore respecting the atom is electrically neutral.In charge of the nucleus of an atom are arranged in sequence and in the periodic table, but their weight sometimes do not obey this law.Therefore, there are cases-exceptions when a heavy atom in the sequence table is earlier.Well, for this is solely to blame isotopes.Nature "wanted" that was a lot of heavy isotopes for a given element.But the relative atomic mass is proportional to the exhibit number of different isotopes.Simply put, if in nature more than heavy isotopes - atomic weight will be more if more light - then the smaller ones.So it is a paradox of the Mendeleev.
In fact, said the atomic weight of several simplified.There are deeper and more severe laws on the periodic table.But they require a separate article, perhaps we will return to consider them later, dear reader.
