Periodic table

The periodic table of the chemical elements, also called the Mendeleev periodic table, is a tabular display of the known chemical elements. First created by Dmitri Mendeleev, the elements are arranged by electron configuration so that many chemical properties follow a regular pattern across the table. Each element is listed by its atomic number and chemical symbol. Mendeleev's ordering of the periodic table was one of the greatest developments in modern chemistry. Chemists were able to quantitatively explain the behavior of the elements, and to predict the existence of yet undiscovered ones. There are 116 chemical elements whose discoveries has been confirmed. Ninety four can be found naturally on Earth, and the rest have been produced in laboratories.

Periodicity of chemical properties

Elements adjacent to one another within a group have similar physical properties, despite their significant differences in mass. Elements adjacent to one another within a period, or energy level, have similar mass but different properties.

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For example, very near to nitrogen (N) in the second period of the chart are carbon (C) and oxygen (O).

Related Topics:
Nitrogen - Carbon - Oxygen

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Despite their similarities in mass (only a few atomic mass units), they have extremely different properties, as can be seen by looking at their allotropes: diatomic oxygen is a gas that supports burning, diatomic nitrogen is a gas that does not support burning, while carbon is a solid which can be burned. Diamonds which are a form of crystallized carbon can also burn.

Related Topics:
Atomic mass unit - Allotropes - Gas - Solid - Burned - Diamond

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In the group known as the halogens, the element chlorine (Cl) falls between fluorine (F) and bromine (Br).

Related Topics:
Halogen - Chlorine - Fluorine - Bromine

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Despite their dramatic differences in mass, their allotropes have very similar properties. They are all highly corrosive. Chlorine and fluorine are gases, while bromine is a very low-boiling liquid. Chlorine and bromine are brightly colored, whereas flourine is not.

Related Topics:
Corrosive - Liquid

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