1.1.13

Periodic Table

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The Periodic Table

The periodic table is an ordered arrangement of all 118 known elements. The elements are arranged in order of their atomic number (number of protons). Every time you move an element to the right, the proton number increases by 1.

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Periods

  • The table is ‘periodic’ because elements with similar properties are found at regular intervals, i.e. periodically.
  • So, the rows of the periodic table are called periods.
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Groups

  • Elements in the same column have the same number of electrons in their outer shell (the highest energy level).
  • Columns are known as groups, and the group number equals the number of electrons an atom of that element has in its outer shell.
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Predicting chemical properties

  • Because all elements in a column have the same number of electrons in their outer shell, they have similar chemical properties.
  • This means they will all react in similar ways.

History of the Periodic Table

Before scientists discovered sub-atomic particles (protons, neutrons and electrons), they tried to sort elements by their mass. Today, we rank elements by their atomic number (the number of protons in an atom's nucleus).

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Newlands' periodic table

  • John Newlands was the first chemist to devise a periodic table.
  • Newlands' periodic table was ordered by the mass of the element.
  • But, the table was incomplete, and some elements were placed in inappropriate groups.
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Mendeleev's periodic table

  • Dmitri Mendeleev recognised that there may be undiscovered elements.
  • Mendeleev added gaps to Newlands’ table to account for undiscovered elements.
  • Mendeleev even predicted the properties and masses of these undiscovered elements!
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The modern periodic table

  • The discovery of protons and isotopes has shown that Mendeleev ordered elements exactly by relative atomic mass.
  • Therefore, the modern periodic table looks very similar to Mendeleev's (except the gaps are filled).

Jump to other topics

1Atomic Structure

2Chemical Bonding

3Quantitative Chemistry

4Chemical Changes

5Energy Changes

6The Rate & Extent of Chemical Change

7Organic Chemistry

8Chemical Analysis

9Chemistry of the Atmosphere

10Using Resources

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