Difference Between Periods and Groups l Periods vs Groups

The key difference between periods and groups is that the periods are horizontal rows whereas the groups are the vertical columns in the periodic table of chemical elements. There are 7 major periods and 18 groups in the periodic table of elements.

The periodic table of elements is a large table in which each and every known chemical element is placed in a specific location considering the atomic structures. Hence, as with any grid, this periodic table also has rows and columns. Further, each row and column has specific characteristics, and we name a row as a period and a column as a group in the periodic table.

1. Overview and Key Difference
2. What are Periods in Periodic Table
3. What are Groups in Periodic Table
4. Side by Side Comparison – Periods vs Groups in Tabular Form
5. Summary

What are Periods in Periodic Table?

Periods are the horizontal rows in the periodic table. All the chemical elements in this row have the same number of electron shells. When we go through a row, the number of protons in the atomic nucleus increases by 1 for each next element in the period. Moreover, the elements get less metallic when we move forward a row.

However, the periods have different numbers of members; there are more chemical elements in some periods than some other periods. This is because, the number of elements is determined by the number of electrons allowed in each electron shell. Mainly, there are 7 periods in the periodic table. Thus, we name them as period 1, period 2, … Period 7.

What are Groups in Periodic Table?

Groups are the vertical columns in the periodic table. All the chemical elements in the same group contain an equal number of valence electrons. For example, the number of valence electrons in the group 1 is 1. Most of the times, the elements in the same group shares somewhat similar chemical and physical properties. There are mainly 18 groups in the periodic table. However, some groups have common names as well. For example, we call the group 1 element as alkali metals and group 2 elements as alkali earth metals.

Figure 01: Periods and Groups in the Periodic Table

Some of these common names are as follows:

Group 1 = alkali metals
Group 2 = alkaline earth metals
Group 11 = coinage metals
Group 12 = volatile metals
Group 17 = halogens

What is the Difference Between Periods and Groups in Periodic Table?

Periods are the horizontal rows in the periodic table whereas groups are the vertical columns in the periodic table. Hence, this is the key difference between periods and groups of the periodic table. There are 7 major periods and 18 groups in the periodic table of elements. Furthermore, we can also find another difference between periods and groups in the eletron arrangement. That is, the elements in the same period have the same number of electron shells while the elements in the same group have the same number of valence electrons.

Summary – Periods vs Groups

To sum up what we discussed here, periods and groups are two ways that we categorize the chemical elements in the periodic table. And, the key difference between periods and groups is that periods are horizontal rows whereas groups are the vertical columns in the periodic table of chemical elements.

Reference:

1. Helmenstine, Anne Marie, Ph.D. “The Difference Between an Element Group and Period.” ThoughtCo, Aug. 3, 2017. Available here
2. Intermediate, CK12. “Chemistry for Non-Majors.” Lumen, Lumen Learning. Available here