Albert Einstein gave a quantitative interpretation of Brownian motion in and made the concept of atoms real by showing that the "jiggling" motion could be accounted for by collisions of water molecules with the pollen grains. Yet, even before Einstein, the clues were there.
The Law of Definite Proportions: 8 grams of the oxygen will combine with 1 gram of hydrogen to give the 9 grams of water, a ratio of 8 to 1. If one part of hydrogen combines with eight parts of oxygen all of the time, then it could be that an oxygen atom is eight times as massive as a hydrogen atom, and when the two come together they make a water molecule that is nine times as massive as hydrogen.
This is incorrect! The correct picture is that two hydrogen atoms combine with one oxygen atom and that the mass of oxygen is 16 times as great as hydrogen. The ratio of 2 to 16 is the same as 1 to 8. In other words, you need more information than the ratio of masses that combine to determine how many atoms of each are involved.
The ratio of the masses doesn't tell you that two hydrogen atoms combine with one of oxygen to make water. Hence, hydrogen is an element made of an aggregate of hydrogen atoms while oxygen is an element made of oxygen atoms. However, water is a compound made of water molecules. Note that the molecules which form a compound are made of different types of atoms, but molecules can also consist of atoms of the same kind.
In particular, hydrogen and oxygen are normally found as molecules formed by two atoms stuck together. Mixtures are different than compounds in that the properties of the constituents in a mixture don't change. Water has very different properties from hydrogen or oxygen. The sugar remains sugar and the water remains water.
A particularly interesting large molecule is formed solely by carbon atoms in a rigid structure that resembles the architectural structure invented by Buckminster Fuller, the famous architect. These, so-called, buckyballs were discovered in and in solid form in This atom molecules is called a icosahedron 20 faces consisting of pentagons and hexagons. Like its architectural analog, these are particularly strong molecules. This is because the chemical structure remains the same, but the molecules of which it consists will float a little further apart.
In the solid state the water molecules are fairly close together, but in the liquid state they are a bit further apart.
The water becomes liquid as a result of parting molecules. When water changes from liquid to gas the molecules will part even further, that is why we cannot detect it. When substances freeze, usually the molecules come closer together. Water has an abnormality there: it freezes below 0 o C, but when temperatures goes below 4 o C, water starts to expand again and as a result the density becomes lower.
Density of a substance means the weight in kilograms of a cubic metre of a substance. When two substances are mixed but do not dissolve in one another, the substance with the lowest density floats on the other substance.
In this case that substance is ice, due to the decreased density of water. Polarity determines if a substance is water-soluble. A polair substance is a substance that has two kinds of 'poles', as in a magnet. When another substance is also polair the poles of the substances attract each other and as a result the substances mix. A substance then dissolves in water.
Substances that contain no 'poles' are called apolair substances. Oil for instance is an apolair substance, which is why oil does not dissolve in water. In fact it floats on water, just like ice, due to its smaller density. When water is referred to as 'hard' this simply means, that it contains more minerals than ordinary water. These are especially the minerals calcium and magnesium. The degree of hardness of the water exceeds, when more calcium and magnesium dissolve.
Magnesium and calcium are positively charged ions. Because of their presence, other positively charged substances will dissolve less easy in hard water than in water that does not contain calcium and magnesium. This is the cause of the fact that soap doesn't really dissolve in hard water. For more information on hard water check out the water softener FAQ. Physical properties of a substance are properties that have everything to do with the substance's appearance.
Chemical properties are properties that are often used in chemistry, to address the state of a substance. Physical and chemical properties can tell us something about the behaviour of a substance in certain circumstances. There are several different physical and chemical properties, which are often used alternately.
We can name the following: - Density. The density of water means the weight of a certain amount of water. It is usually expressed in kilograms per cubic metre. This refers to what happens to water when it is heated; at which temperature it becomes gaseous and that sort of thing. Everything dissolves in water. Stone, iron, pots, pans, plates, sugar, salt, and coffee beans all dissolve in water.
Things which dissolve are called solutes and the liquid in which they dissolve is called a solvent. The water molecules surround the charged solute; positive hydrogens close to negative charges and negative oxygens close to positive charges on the solute molecule. All this interaction suspends the solute molecule in a sea of water molecules; it disperses and dissolves easily. Electrons in the bonds between identical atoms H-H are shared uniformly, so the electrons spend equal amounts of time around each atomic center.
These covalent bonds are non-polar. Electrons shared between unlike atoms are not shared equally, one atom gets more of the common electrons and is thus slightly negatively charged. The other atoms gets less than a full share of the electrons and is thus slightly positively charged. Substances which dissolve easily and readily in water sugar, salt, etc. On the other hand, some solutes are non-polar and do not have any positive or negative charges.
Water molecules are not attracted to these types of molecules and, in fact, are sometimes repelled by them.
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