Groups in chemistry refer to the arrangement of elements of the periodic table into vertical columns. These vertical columns, called groups, are numbered from 1 to 18 and run from top to bottom. The first column on the left is labelled Group 1, and the last column on the right is labelled Group 18.
The elements in the group have the same number of electrons (valence electrons) in their outermost shell, also known as the valence shell, due to which they all have the same chemical or physical properties.
Group number | Valence Electrons |
|---|---|
1 | 1 |
2 | 2 |
3-12 | 2 |
13 | 3 |
14 | 4 |
15 | 5 |
16 | 6 |
17 | 7 |
18 | 8 |
For example, all the elements of group 1 having only one electron in their outermost shell are called alkali metals because they all can readily react with water to form alkaline solutions. Alkaline solutions are basic in nature and have a pH greater than 7. Similarly, all the elements of group 17 have the unique ability to react with metals and form salts.
The groups may also be identified by their topmost element; for example, group 15 is called the Nitrogen group, and group 16 is also known as the Oxygen group. An exception to this rule is the Iron group, which must refer to group 8 but includes other elements from different groups, like cobalt and nickel.
While these groups were arranged to accommodate all 118 elements of the periodic table based on their properties, it is important to note that the elements belonging to the f-block series (La-Yb and Ac-No) have not been assigned any specific group number. They are presented as separate rows, the lanthanides and actinides, placed below the main body of the table.
As per the IUPAC recommendations in 1988 and 2021, the correct elements of Group 3 are Scandium, Yttrium, Lutetium, and Lawrencium. The elements La to Yb are inserted between Barium and Lutetium, and Ac to No between Radium and Lawrencium.
Sources:
New Notations in the Periodic Table
Which Elements Belong in Group 3?
To understand how electrons are distributed at different levels, the difference between inner core electrons and outer valence electrons, and the influence of outer valence electrons on reactivity, read the chapter on Atoms, part of the Organic Chemistry Fundamentals Course.