complex composition of substances, although they are formed by tiny particles - atoms, molecules, ions.The molecular structure have many liquids and gases, as well as some solids.Atoms and ions comprise metals, many salts.All particles have mass, even the tiny molecule.The mass of the molecule, to put it in kilograms, a very small value.For example, m (H2O) = 30 • 10-27 kg.These important characteristics of a substance as the weight and size of the microparticles, have long studied physics and chemists.The foundations were laid in the works of Mikhail Lomonosov and John Dalton.We consider how changed since views on the microcosm.
Performances University of "corpuscles»
assumption of the discrete structure of matter expressed by scientists of ancient Greece.Then it was given the name "atom" the smallest indivisible particles of bodies, "building blocks" of the universe.The great Russian scholar Mikhail Lomonosov wrote negligible, indivisible physical means particle structure of matter - corpuscle.Later, in the works of other scholars, she was named "molecule".
mass of the molecule, as well as its size, determined by the properties of its constituent atoms.Scientists have long been able to look deep into the microcosm that hindered the development of chemistry and physics.Lomonosov repeatedly urged colleagues to study in its work to rely on accurate quantitative data - a "measure and weight."Through the work of Russian chemist and physicist they laid the foundations of the doctrine of the structure of matter, which have become an integral part of coherent atomic-molecular theory.
atoms and molecules - "building blocks of the universe»
Even microscopically small hard bodies are arranged, have different properties.Particles such as atoms, formed by the core and electronic layers differ in the number of positive and negative charges radius weight.Atoms and molecules exist in the composition of substances is not isolated, they are attracted to different power.More noticeable effects of attractive forces in solids, less - in liquids, hardly felt in the gaseous substances.
Chemical reactions are not accompanied by the destruction of atoms.The most common is their rearrangement, there is another molecule.Mass molecule depends on what atoms it is formed.But with all the changes in the atoms are chemically indivisible.But they can enter into the composition of the different molecules.At the same time retain the properties of the atoms of the element to which relate.Molecule before decaying into atoms retains all the signs of substance.
microparticle structure of bodies - the molecule.The mass of the molecule
to measure the mass of armatures used devices, the oldest of which - the scales.The measurement result is conveniently prepared in kilograms, as the basic unit of the international system of physical quantities (SI).To determine the molecular weight in kilograms, it is necessary to lay down their atomic weights based on the number of particles.For convenience, we have introduced a special unit of mass - nuclear.You can write it in the form of letter abbreviations (amu).This unit corresponds to one twelfth of the mass of the carbon nuclide 12C.
If we express the value found in standard units, we obtain 1,66 • 10-27 kg.Such low rates of mass bodies operate mainly physics.The article is a table from which you can learn what are the masses of the atoms of certain chemical elements.To find out what is the mass of a single molecule of hydrogen in kilograms, multiply the two shown in the table atomic weight of this element.The result is a value of the mass of the molecule consisting of two atoms.
Molecular mass
is difficult to operate in the calculation of very small quantities, it is inconvenient, leads to time-consuming, error-prone.With regard to the weight of the microparticles, the way out of a difficult situation was the use of relative values.The usual term for chemists consists of two words - "atomic weight," its designation - Ar.Identical concept was introduced to the molecular weight (the same as the mass of the molecule).The formula that relates the two quantities: Mr = m (to target) / 1/12 m (12C).
Often you can hear what they say, "molecular weight".This obsolete term still used in reference to the mass of the molecules, but more rarely.The fact that weight - is another physical quantity - a force that depends on the geographical coordinates of the body.In contrast, the mass is a constant characteristic of the particles that participate in chemical processes, and are moved at normal speed.
How to determine the mass of the molecule
precise definition of the weight of the molecule is carried out using the instrument - a mass spectrometer.To solve the problems, you can use information from the periodic table.For example, the mass of a molecule of oxygen is 16 2 = 32. • Perform simple calculations and find the value of Mr (H2O) - a relative molecular mass of water.On the periodic table determine the mass of an atom of oxygen - 16, hydrogen - 1. Draw simple calculations: Mr (H2O) = 1 • 2 + 16 = 18, which Mr - molecular weight, H2O - water molecule, H - the symbol of the element hydrogen,About - chemical sign of oxygen.
isotope mass
Chemical elements in nature and technology, there are a few species of atoms - isotopes.Each of them has an individual weight, its value can not be a fractional value.But the atomic weight of a chemical element often is the number of multiple characters after the decimal point.When the calculations take into account the prevalence of each species in the Earth's crust.Therefore, the mass of the atoms in the periodic table are not always integers.Using these values for the calculation we get the mass of molecules that also are not integers.In some cases, the values may be rounded.
molecular weight of non-molecular structure of substances
Most inorganic compounds do not have the molecular structure.Metals are composed of atoms, ions and free electrons, salts - of cations and anions.For substances of non-molecular structure as conventional molecular weight is calculated by empirical formula reflecting the simplest part.We find the Mr the ionic structure of the substance - salt, the formula is NaCl.Mr = 23 + 35.5 = 55.5.For some types of calculations required molecular weight of air - gas mixture.Taking into account the percentage of various substances in the atmosphere of the molecular weight of air is 29.
size and mass of the molecules
in electron micrographs of large molecules can consider the individual atoms, but they are so small that an ordinary microscope can not be seen.Linear particle size of any substance, as well as mass - this is a permanent characteristic.The diameter of the molecule depends on the radius of its constituent atoms, their mutual attraction.The particle sizes vary with the number of protons and energy levels.The hydrogen atom - the smallest in size, its range is only 0.5 • 10-8 cm. Uranium atoms is three times more hydrogen atoms.These "giants" of the microcosm - the molecules of organic substances.Thus, the linear dimension of a protein particle is 44 • 10-8 cm.
summarize: the mass of molecules - is the sum of the masses of atoms within them.The absolute value in kilograms can be obtained by multiplying the molecular weight found in the periodic table, the magnitude 1,66 • 10-27 kg.
molecules negligible compared to the macro-bodies.For example, in size water molecule H2O gives the apple as many times, how many times this fruit is smaller than our planet.
