The arrangement of the periodic table

In a nutshell

​The periodic table is arranged in order of increasing atomic number. The periodic table can also be used to predict the properties of elements based on their position as the table shows trends and similarities of certain elements. A scientist named Mendeleev organised the periodic table in this way. 

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Mendeleev's creation of the periodic table 

Metals and non-metals

One of the ways in which the periodic table is organised is the separation of metals and non-metals. On the left side of the table are the metals and on the right side are the non-metals.

There are some elements which have a combination of metallic and non-metallic properties. These are found along the border which separates the metals and non-metals. Boron, silicon, arsenic and so on. These elements are called metalloids or semi-metals. For example, boron conducts electricity at high temperatures but at room temperature it acts as an insulator. 

The s-, p-, d- and f- blocks

The periodic table also shows in which orbital an element's highest energy electron can be found. The elements which have their highest energy electron in an $$s$$​-orbital will be found in the $$s-$$​block. Those found in the other blocks ($$p-,\,d-$$​ or $$f-$$​ block) will also have their highest energy electron in a shell corresponding to their block.

Example

Sodium ($$1s^{2}2s^{2}2p^{6}3s^{1}$$) will be found in the $$s-$$block.

Groups

A group is a column of elements. The elements in a group have similar properties and the same number of electrons in the outer-shell. The groups are numbered $$1-7$$​ (from left to right) and sometimes $$1-18$$​ including the transition metals. Group $$0$$​ is used to describe noble gases. 

Periods

A period refers to a row in the periodic table. The first period is period $$1$$​ which contains two elements - hydrogen and helium. The next period is period $$2$$​ containing elements such as boron and carbon. 

Trends in reactivity

Trends can be seen across the periodic table. The reactivity of group $$1$$​ increases as you down the group, but group $$7$$​ halogens become less reactive as you go down a group. 

The centre of the periodic table contains the transition metals which are a block of unreactive metals. 

Lanthanides and actinides are other groups found in the periodic table. Actinides are radioactive metals. Lanthanides are metals which tend to form ions with a $$3^+$$​ charge and have similar reaction properties.

Trends across a period are also seen such as trends in atomic radii, melting point and boiling points. ​

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