In a nutshell:
- The Periodic Table is a useful way to arrange the elements in order of increasing atomic number.
- Groups are the vertical columns.
- Periods are the horizontal rows.
- Electron configurations can be written using the period to find the number of shells and the group to find the number electrons in the valence shell.
Imagine searching through piles of unsorted CDs looking for the latest album of your favourite artist. Such a task could take days.
Fortunately music shops arrange their CDs in separate sections. They then divide each of these groups into smaller groups according to the type of music, e.g. rock, popular, jazz and classical. Artists within each group are then arranged alphabetically. Scientists have a similar problem to the music store owner. There are over 100 different elements, each with different physical and chemical properties. |
categories
The elements of the periodic table can be broken into three major categories, according to their shared physical and chemical properties: metals, metalloids (or semi-metals) and nonmetals.
This periodic table shows the three different categories of elements. The metalloid group separates the metals from the nonmetals. Elements to the left are metals and nonmetals are to the right. The exception is the element hydrogen. Hydrogen has properties of a nonmetal at normal temperatures and pressures while it has metallic properties in the solid state.
- Metals are generally shiny, highly conducting solids that form alloys with one another and salt-like ionic compounds with nonmetals (other than the noble gases).
- The majority of nonmetals are gases. Carbon, phosphorus, sulfur, selenium, iodine and the rarely used astatine are solids while bromine is the only liquid nonmetal element; nonmetals form compounds with other nonmetals through covalent bonding, while they react with metals to form ionic compounds.
- In between metals and nonmetals are metalloids, or semi-metals, which have intermediate or mixed properties.
This periodic table shows the three different categories of elements. The metalloid group separates the metals from the nonmetals. Elements to the left are metals and nonmetals are to the right. The exception is the element hydrogen. Hydrogen has properties of a nonmetal at normal temperatures and pressures while it has metallic properties in the solid state.
- The periodic table is simply a list of the chemical elements arranged in order of increasing atomic number. Reading like a book from left to right and top to bottom, the atomic number increases in single units from 1 to 118.
- The arrangement is such that similar elements are found next to one another in repeating cycles or periods. From this pattern comes the term 'The Periodic Table'. A number of trends in chemical and physical properties of the elements can be recognised and will be discussed in the next section.
- However, the Periodic Table is more than just a list of elements. Its clever structure makes it one of the most useful datatables in all of science, providing information on the chemical and physical properties of elements, depending on their position in the table. Hence its ubiquitous place of honour on laboratory walls. Mendeleev himself left some empty spots in his early periodic table for yet undiscovered elements (most notably elements that he named eka-boron (Eb), eka-aluminium (Ea), eka-manganese (Em), and eka-silicon (Es), later to be renamed as scandium, gallium, technetium and germanium upon their discovery) and predicted some of their physical and chemical properties. His predictions were later found to be in close agreement with experimental measurements.
- The most common layout of the Periodic Table is shown below, although alternative layouts have been proposed. Click here to obtain more information on different presentations of the Periodic Table.
Groups (or families)
The vertical columns of elements are known as groups, numbered from 1 to 18.
Some of the groups are also referred to by group names (in times past, they all had names). The most well-known are:
Group number 1: alkali metals
Group number 2: alkaline earth metals
Group number 17: halogens
Group number 18: noble gases
Groups 3 to 12 contains the transition metals
Elements of the same group share similar chemical properties owing to the similarity of electronic configuration in terms of the outer (valence) electron shell. For example, group 1 - the alkali metals all have one electron in the outer shell. They are all soft metals, which react with water making metal hydroxides.
Hydrogen is the only element of elements among the first 20 elements that does not easily fit into any of the groups. For this reason it is sometimes to be found suspended in no-man's land, in the middle of the periodic table.
Some of the groups are also referred to by group names (in times past, they all had names). The most well-known are:
Group number 1: alkali metals
Group number 2: alkaline earth metals
Group number 17: halogens
Group number 18: noble gases
Groups 3 to 12 contains the transition metals
Elements of the same group share similar chemical properties owing to the similarity of electronic configuration in terms of the outer (valence) electron shell. For example, group 1 - the alkali metals all have one electron in the outer shell. They are all soft metals, which react with water making metal hydroxides.
Hydrogen is the only element of elements among the first 20 elements that does not easily fit into any of the groups. For this reason it is sometimes to be found suspended in no-man's land, in the middle of the periodic table.
Periods
The horizontal rows, or periods, give the periodic table its name. Each period represents the elements in which the same electron shell is being filled by electrons, until it is full.
Thus, the second period has elements with an incomplete second energy level (except for neon, in which the second level is now full).
Thus, the second period has elements with an incomplete second energy level (except for neon, in which the second level is now full).