To organise the Periodic Table, the elements are first arranged in order of increasing atomic number. The atomic number is the number of protons in the nucleus. The elements are then organised so that elements with the same number of electrons in their outermost shell are in the same column. The columns on the Periodic Table are called groups. Elements in a group have similar properties. The Periodic Table gives us a lot of information about elements, for example elements in
Group 1 are very reactive and readily take part in chemical reactions, while elements in Group 8 are very unreactive. The elements were first arranged in this way by a scientist called Dmitri Mendeleev in 1869. The modern Periodic Table is very similar to Mendeleev’s.
Science in Society Find out about the life and work of Dmitri Mendeleev. Include how his Periodic Table differs from the Periodic Table used today in science classrooms around the world. You can present this in a PowerPoint presentation, on a poster or as a booklet.
The elements on the left of the Periodic Table are called metals, the elements on the right are called non-metals. There are a few elements which are called metalloids. These are very useful because under some conditions they behave like metals and conduct electricity, and under other conditions they behave like non-metals and they do not conduct electricity.
Activity Investigate the properties of alkaline earth metals (Group 2)
Calcium and magnesium are both elements in Group 2. Using a sample of each, examine and describe their properties.
Property Colour
Solid/liquid/gas Reaction with dilute hydrochloric acid* Reaction with water** (what gas forms)
*Warning: Addition of calcium to HCl should be demonstrated by a teacher. **To see if magnesium reacts with water you can set up an experiment like the one shown in Fig. 6. After a few days the test tube will contain some gas. You can test this gas to identify it (see Chapter 19, page 211).
Fig. 6 To show magnesium reacts with water. 251 Calcium Magnesium
