- •Chemistry
- •Introduction
- •Some facts about chemistry
- •Some facts about atoms (I)
- •Some facts about atoms (II)
- •The atomic model
- •The nature of ceramics
- •Construction materials
- •The measurements in chemistry
- •The metric system
- •Isotopes
- •Words to be remembered:
- •Notes on the text:
- •Liquids(I)
- •Words to be remembered:
- •Liquids (II)
- •Words to be remembered:
- •Solid state (I)
- •Words to be remembered:
- •Solid state (II)
- •Words to be remembered:
- •Properties of solids
- •Notes on the texts:
- •Words to be remembered:
- •Organic chemistry
- •Word to be remembered:
- •Elementary carbon
- •Words to be remembered:
- •Notes on the texts:
- •Carbon dioxide
- •Words to be remembered:
- •Words to be remembered:
- •Hydrogen
- •Words to be remembered):
The measurements in chemistry
In order to understand the quantitative relationships which exist between various kinds of matter, the chemist who is interested in matter and changes which it undergoes, has to measure the quantities of matter with which he works, that is since mass is the measure of the quantity of matter, he is to measure mass. The measuring device the chemist is to employ in this determination should be the balance.
Since for every chemical change there is always accompanying energy change which the chemist has to take into account, the calorimeter and the thermometer have to be used.
The chemist usually employs graduated cylinders, burettes, pipettes and volumetric flasks tor the measurements of volumes of liquids, and the gas burette for the measurement of volumes of gases.
The chemist employ the barometer if he has to measure the pressure. The analytical chemist and the physical chemist employ such devices as calorimeters, polarimeters, refractoraeters and a number of electrical devices.
If the chemist is to examine very small samples of matter, he should use a microscope. The microscope is an instrument which by the combination of lenses permits man to see objects which are too small to be seen with a naked eye; It is an instru ment which is useful in many sciences and which, although more frequently used in a qualitative way, can also be used quanti-
tavely.
The metric system
The fundamental unit of the metric system is the metre. The millimeter and centimetre axe the units which the ohemiet uses very frequently in his work. If one is to measure exlxesely short distances, the micron is to be used.
The unit of mass is the ахов» milligram or the kilogram.
The unit of the heat measurement is the calorie.
Words to be remembered:
in order to burette
quantitative flask
to undergo volumetric
relationship pressure
device sample
determination unit
balance frequently
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Isotopes
The word “isotope” is derived from the Greek “isos”, “topos” and means “the same place”.
Hence, isotopes are atoms having the same atomic number, but differing in atomic weight (mass number), e.g. ¹²9C and ¹³6 C are isotopes of carbon, or one out of every 5,000 atoms of hydgen has an atomic weight of 2.016 instead of 1.008.
This odd atom has a neutron in its nucleus as well as a proton, it being known as heavy hydrogen. The water containing it is known as heavy water.
Isotopes occur with considerably greater frequency in other elements than in hydrogen, an extreme case being chlorine, its afomic weight being 35.5. It is made up of two groups of atoms in a ratio of 3:1, the weight of one group being 35, that of the other 37.
In the case of uranium, for example, one isotope of atomic weight 235 is found in every 40 atoms of the standard weight, with the weight being 238.
The chemical properties of isotopes being identical with
those of regular atoms, their discovery was of little interest to chemists. Physicists, however, got interested in them, a new way of approaching to the structure of matter being opened.