The periodic table arranges all the elements by their chemical and physical properties.
Elements are everywhere: some we can see, such as, silver, gold (Figure 1), sodium, while others are invisible, such as, oxygen, helium, hydrogen.
Most elements combined with other elements to make compounds. For example, water, made of hydrogen and oxygen (Figure 2).
Importance of Periodic Table
There are 118 elements in the periodic table; 92 are found in nature, while the others are man-made. Every element is unique.
At room temperature, most of the elements are solids, 11 are gases, whereas bromine and mercury are liquids.
The first person to understand the elements was the Irish scientist and inventor Robert Boyle.
In the early 19th century, the English scientist Humphry Davy discovered several new metals.
He used electrolysis, in which electric currents split chemical compounds into their elements to discover nine new elements.
Arrangement of Elements in a Periodic Table
The periodic table is a useful way of organizing the elements by their recurring chemical and physical properties.
In 1869, Dmitri Mendeleev published the periodic table, which helps in organizing the atomic elements into columns and rows. Therefore, finding properties of these elements.
Elements in the same group are like each other. The elements (Figure 3) are arranged in order of increasing atomic number.
The modern periodic table (Figure 4) is also closely related on the discovery of new elements.
Mendeleev left spaces for elements yet to be discovered and predicted their existence based on the patterns in the table.
Gallium was discovered in 1875 and germanium in 1886.
The vertical columns of the periodic table, called groups, have the following arrangement.
- Elements of group 1 are called alkali metals
- Elements of group 2 are called alkaline earth metals
- Elements of group 16 are called chalcogens (Ore-forming elements)
- Elements of group 17 are called halogens
- Elements of group 18 are called noble gases
The horizontal rows of the periodic table, called periods, are arranged as follows:
- First period (1H – 2He) contains 2 elements. It is the shortest period
- Second period (3Li – 10Ne)
- Third period (11 Na – 18Ar)
- Fourth period (19K – 36Kr)
- Fifth period (37Rb – 54Xe) contain 18 elements.
- Sixth period (55Cs – 86 Rn) consists of 32 elements and is the longest period.
- Seventh period starting with 87Fr is incomplete and consists of 19 elements.