The Periodic Table
This is a table on which elements are systematically arranged into GROUPS and PERIODS.
Definition of terms:
Valence electrons: These are the outermost electrons in an electron shell. Given Na with atomic number 11 and electronic configuration 2,8,1, its valence electron is 1.
Electron shells:These ate “houses” where electrons are srranged systematically. There are various electron shells. Thse include;
The maximum number of electrons a shell can hold can be calculated using the formular2n2, where n is the number of electron shell.
Electronic Configuration: This is the systematic arrangement or distribution of electrons in electron shells or orbitals (also called sub-shells). Given an element like Na with atomic number 11, its electronic configuration will be 2,8,1ie 2+8+1=11, Also for Ca with atomic number 20, its electronic configuration will be 2,8,8,2.
Group: Elements with the same valence electrons belong to the same groupon the periodic table.
. For instance, Boron has atomic number 5 with electronic configuration 2,3; and Al which has atomic number 13 with electronic configuration 2,8,3. Both have 3 as the valence electrons and so belong to group 3 on the periodic table.
Periods:Elements with the same number of electron shell belong to the same Period on the periodic table. Given Boron with electronic configuration 2,3 and Nitrogen with electronic configuration 2,5. Both have two electron shells, and so belong to Period 2. Also, Na with electronic configuration 2,8,1 and Al with 2,8,3 both have three electron shells and so belong to Period 3 on the table.
The periodic table of the first twenty elements with their electronic configurationis shown below:
|PERIOD I||H 1||He 2|
|PERIOD II||Li 2,1||Be 2,2||B 2,3||C 2,4||N 2,5||O 2,6||F 2,7||Ne 2,8|
|PERIOD III||Na 2,8,1||Mg 2,8,2||Al 2,8,3||Si 2,8,4||P 2,8,5||S 2,8,6||Cl 2,8,7||Ar 2,8,8|
|PERIOD IV||K 2,8,8,1||Ca 2,8,8,2|
Classification of elements based on their Groups on the Periodic table
Based on the group elements belong to on the Periodic table, they can be classified as:
|Group||Name of group|
|II||Alkali Earth metals|