The periodic table is a visual arrangement of the elements according to their atomic number. The effort to create the periodic table began in the 19th century when scientists observed that properties of elements recur periodically when the elements are arranged in the order of their atomic weights. The modern periodic table organizes elements into 7 rows, or periods, and 18 columns, or groups. This arrangement leads to easy visualization of trends in atomic radius, nuclear charge, electronegativity, electron affinity, and ionization energy.
At A Glance
- In the 19th century, scientists began developing methods to arrange the elements in a logical order according to periodic law, the observation that the chemical and physical properties of the elements recur periodically when the elements are arranged in the order of their atomic weights.
- The modern periodic table arranges the elements by atomic number in 18 vertical columns, called groups, and 7 horizontal rows, called periods.
- The periodic table arranges elements in a meaningful way, which allows for trends in atomic radius, nuclear charge, electronegativity, electron affinity, and ionization energy to be easily determined.
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Atomic radius decreases from left to right across the periodic table and increases from top to bottom down the table. Nuclear charge increases from left to right across the periodic table and from top to bottom down the periodic table.
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Electronegativity increases from left to right across the periodic table, with a few exceptions, and decreases from top to bottom down the periodic table. Electron affinity increases from left to right across the periodic table and decreases from top to bottom down the periodic table.
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Ionization energy increases from left to right across the periodic table and decreases from top to bottom down the periodic table.
