The Periodic Table of Elements

Each element has been given a distinct name. Often the name was given to the element by the scientist who discovered the element. 

Each symbol also has a chemical symbol - a letter code for the element. For example, C is the code for carbon, N for nitrogen, and S for sulfur. 

Some elements have single-letter codes, but most have two-letter codes, e.g. Mg for magnesium. 

Most symbols are derived from the element's English name, but a few come from the element's name in another language. 

The elements are arranged on a chart called the Periodic Table. They are arrnaged in order fromteh lowest Atomic Number across rows. Each row relates to electron energy shells - the first row has two elements, the second row has eight elements, the third row has eight elements etc. 

A column of elements is called a group and elements in a group have similar properties. 

Reading information off a Periodic Table: 

1. Locate the name of the element (e.g. Sulfur) - the box will give you the chemical symbol (S). 

2. In the box, find the Atomic Number (16 - a sulfur atom has 16 protons and therefore 16 electrons). 

3. From its position along a row, you can tell whether it has a full or partly full shell (sulfur has six electrons in its outer shell - two short). 

4. From the colour code on the chart, identify whether it is a metal or a non-metal (sulfur is a non-metal). 

The periodic table will always be accessible to you at the back of your test paper or assessment, Knowledge book or workbook. But I strongly suggest you memorise the first 20 elements (name, symbol and atomic number).

In the 19th century, science expanded at a rapid rate. Chemists like Antoine and Marie Lavoisier and John Dalton led the way in discovering the different elements. 

In 1829, Johann Dobereiner showed that some elements could be grouped in threes, according to their similar properties. 

In 1863, John Newlands noted that there were eight groups of elements. 

In 1869, Dimitri Mendeleev published a periodic table with the elements in order of increasing atomic number. Elements with similar properties were placed in vertical groups. He left gaps for elements that had not yet been found, predicting that they would be discovered. He was right - later, gallium and germanium filled two of these gaps. 

When sodium metal is carefully dropped ino water, it reacts with water, becoming so hot that it melts into a ball and whizzes around on the surface. Lithium and potassium also react with water: lithium is less reactiv than sodium, while potassium is more reactive - it is likely to explode dangerously. Watch the videos below - the fourth video shows how rubidium and caesium also react in a similar but more violent way.

The subatomic make-up of atoms had not yet been discovered when the periodic table was published, so no one knew why the elements in a group had similar properties. When we look at the electron arrangements of the atoms in each group, it is clear that:

• Group 1 elements have 1 valence (outer shell) electrons

• Group 2 elements have 2 valence electrons

• Group 17 elements have 7 valence electrons

• Group 18 elements have a full outer shell. 

Atoms react with each other in order to swap electrons to either empty or fill their outer shells. Those with one or two electrons (in the valence shell) try to lose electrons, while those with six or seven try to gain electrons. The Group 18 noble gases do not need to lose or gain electrons, so they are unreactive.