Atoms & atomic structure
Reactions & Compounds
New substances are formed by chemic reaction. When elements react together to form compounds their atoms to other atoms using chemical bonds. For example, iron and Sulfur- often spelt 'sulphur'- react together to form a compound call iron sulfide- often spelt 'sulphide' - and sodium and oxygen react together to for sodium oxide. Chemical bonds involve electronic from the reacting atoms. Bonds can form when: Electrons are transferred from one atom to another, so that one atom gives electrons and the others take electrons or, electrons are shared between two atoms.
Chemical symbol
The atoms of each element are represented by chemical symbols. These usually consist of one or two different letters, bt sometimes three letters are used for newly-discovered element. The first letter in a chemical symbol is always Uppercase, and the other letters are always lowercase. So, the symbol for magnesium is Mg. Every element has its own chemical symbol. For example, iron is Fe, sulphur is S, sodium is Na and oxygen is O.
Chemical formulae
The chemical formula of a compound shows how many of each type of atom join together to make the units that make the compound up. For example, in iron sulfide every iron atoms is joined to one sulfur atom, so we show its formula as FeS. In sodium oxide, there are two sodium atoms for every oxygen atom, so we show its formula as Na2O (small 2). Notice that the 2 is written as a subscript, so Na2O would be wrong. A unit of Na2SO4 contains two sodium atoms, one sulfur atom and four oxygen atoms joined together. A unit of Fe(OH)3 contains one iron atom, three oxygen atoms and three hydrogen atoms- he brackets show that 3 apples to O & H
The periodic table
There are more than 100 different elements, The periodic tables is a chart showing all the elements arranged in a particular way. The vertical columns in the periodic table are called groups. Each group contains elements that have similar properties. The periodic table has 8 main groups. For example, Group 1 contains very reactive metals such as sodium- Na - while group 7 contains very reactive non-metals such as chlorine- Cl.
Balanced equations
We use balanced equations to show what happens to different atoms in reactions. For example, copper and oxygen react together to make copper oxide: Copper + Oxygen = Copper Oxide You can see that copper and oxygen are the reactants, and copper oxide is the product. If we just replace the words shown above by the correct chemical formulae, we will get an unbalanced equation, as shown here: Cu + O2 = CuO Notice that there is unequal numbers of each type of atom on the left hand side compared with the right. To make things equal, we need to adjust the number of units of some of the substances until we get equal numbers of each type of atom on both sides of the arrow. The blanked equation is as follows: 2Cu = O2 = 2CuO You can see we now have two of both Copper and Oxygen on either side.
Equations
When elements are joined to cause a chemical reaction, no atoms are made or lost during the process- but at the en dog it they are joined differently from the way they were at the start. This means that the mass of the substances at the start- the reactions- is the same as the mass of the substances at the end- the products.
