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The periodic table
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The periodic table organises every element. Its layout tells you how an element's atoms are built and how it behaves.
Mendeleev
Dmitri Mendeleev arranged elements by atomic mass and similar properties.
He left gaps for elements not yet discovered, and predicted their properties. When they were found, his predictions were correct.
Today the table is arranged by atomic number.
He left gaps for elements not yet discovered, and predicted their properties. When they were found, his predictions were correct.
Today the table is arranged by atomic number.
Groups and periods
Groups are columns. Elements in a group have the same number of electrons in their outer shell, so they react in similar ways.
Periods are rows. The period number is the number of occupied electron shells.
Periods are rows. The period number is the number of occupied electron shells.
Metals and non-metals
Metals are on the left and centre; non-metals are on the right.
Metals form positive ions; non-metals often form negative ions or share electrons.
Metals form positive ions; non-metals often form negative ions or share electrons.
Sulfur has electronic configuration 2.8.6. Find its group and period.
- 6 electrons in the outer shell: group 6.
- 3 occupied shells: period 3.
Answer: Group 6, period 3
Groups are columns (same outer electrons, similar reactions); periods are rows (number of shells). Mendeleev left gaps for undiscovered elements. Metals left, non-metals right.
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