Page 57 - Curriculum Visions Dynamic Book

monoxide is CO. By using lowercase letters for the second letter of an element, it is possible to show that cobalt, symbol Co, is not the same as the molecule carbon monoxide, CO.
However, the letters can be made to do
much more than this. In many molecules atoms combine in unequal numbers. So, for example, carbon dioxide has one atom of carbon for every two of oxygen.That is shown by using the number 2 beside the oxygen, and the symbol becomes CO2.
In practice, some groups of atoms combine as a unit with other substances.Thus, for example, calcium bicarbonate (one of the compounds used in some antacid pills) is written Ca(HCO3)2.This shows that the part of the substance inside the parentheses reacts as a unit, and the 2 outside the parentheses shows the presence of two such units.
Some substances attract water molecules
to themselves.To show this, a dot is used. So,
the blue form of copper sulphate is written CuSO4.5H2O. In this case five molecules of water are attracted to one of copper sulphate. When you see the dot, you know that this water
Atoms and ions
Each sphere represents a particle of an element. A particle can be an atom or an ion. Each atom or ion is associated with other atoms or ions through bonds – forces of attraction.The size of the particles and the nature of the bonds can be extremely important in determining the nature of the reaction or the properties of the compound.
can be driven off by heating; it is part of the crystal structure.
In a reaction substances change by rearranging the combinations of atoms.The
way in which they change is shown by using the chemical symbols, placing those that will react (the starting materials, or reactants) on the left and the products of the reaction on the right. Between the two an arrow shows which way the reaction is going.
It is possible to describe a reaction in words. That produces word equations, which are given throughoutVolumes 1 to 15. However,
it is easier to understand what is happening by using an equation containing symbols.They are also given in many places.They are not shown when the equations are very complex.
In any equation both sides balance; that is, there must be an equal number of like atoms on both sides of the arrow.When you try to write down reactions, you, too, must balance your equation; you cannot have a few atoms left over at the end!
The symbols in parentheses are abbreviations for the physical state of each substance taking part, so that (s) is used for solid, (l) for liquid, (g) for gas, and (aq) for an aqueous solution, that is, a solution of a substance dissolved in water.
Chemical symbols, equations and diagrams
The arrangement of any molecule or compound
can be shown in one of the two ways shown below, depending on which gives the clearer picture.The left- hand image is called a ball-and-stick diagram because it uses rods and spheres to show the structure of the material.This example shows water, H2O.There are two hydrogen atoms and one oxygen atom.
Bond shown by “stick”
Colours too
The colours of each of the particles help differentiate the elements involved.The diagram can then be matched to the written and symbolic equation given with the diagram. In the case above, oxygen is red, and hydrogen is grey.
Sodium
 This represents
a unit of sodium bicarbonate (NaHCO3).
The term “unit” is sometimes used to simplify the representation of a combination of ions.
This symbol indicates that the compound is ionic.
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