The periodic table has gone through many changes since Dmitri Mendeleev drew up his original table in 1869, yet both the first table and the modern periodic table are important for the same reason: The periodic table organizes elements according to similar properties so you can tell the characteristics of an element just by looking at its location on the table.
Before all of the naturally occurring elements were discovered, the periodic table was used to predict the chemical and physical properties of elements in the gaps on the table. Today, the table can be used to predict properties of elements yet to be discovered, although these new elements are all highly radioactive and break down into more familiar elements almost instantly.
The table is useful for modern students and scientists because it helps predict the types of chemical reactions that a particular element is likely to participate in. Rather than memorize facts and figures for each element, students and scientists need only glance at the table to learn much about the reactivity of an element, whether it is likely to conduct electricity, whether it is hard or soft, and many other characteristics.
Elements in the same column as one other are known as groups and they share similar properties. For example, the elements in the first column (the alkali metals) are all metals that usually carry a 1+ charge in reactions, react vigorously with water, and combine readily with nonmetals.
Elements in the same row as one other are known as periods and they share the same highest unexcited electron energy level.
Another useful feature of the periodic table is that most tables provide all the information you need to balance chemical reactions at a glance. The table tells each element's atomic number and usually its atomic weight. The usual charge on an element is indicated by an element's group.
Trends or Periodicity
The periodic table is organized according to trends in element properties.
As you move from left to right across a row of elements, the atomic radius (the size of an element's atoms) decreases, ionization energy (the energy required to remove an electron from an atom) increases, electron affinity (the amount of energy released when an atom forms a negative ion) generally increases, and electronegativity (an atom's tendency to attract a pair of electrons) increases.
As you move from top to bottom down a column of elements, the atomic radius increases, the ionization energy decreases, electron affinity usually decreases, and electronegativity decreases.
To summarize, the periodic table is important because it is organized to provide a great deal of information about elements and how they relate to one another in one easy-to-use reference.
- The table can be used to predict the properties of elements, even those that have not yet been discovered.
- Columns (groups) and rows (periods) indicate elements that share similar characteristics.
- The table makes trends in element properties apparent and easy to understand.
- The table provides important information used to balance chemical equations.