Difference Between Period and Group (With Table)

Chemistry’s periodic the table is something students are being asked to memorize tediously without even knowing the actual motive behind learning it. For some people, it’s just a topic that’s included in their syllabus. But in a real sense, this little periodic table is way more important than that, it is a roadmap that unlocks a million opportunities for scientists and researchers across the world.

Dmitri Mendeleyev is the inventor of the periodic table. Before him, many gave hard attempts to arrange the chemical elements in different ways. But Dmitri’s outcome was accepted worldwide.  

In scientific abbreviations, the rows are referred as Periods and the columns as Groups respectively.

Period vs Group

The main difference between Periods and Groups is their arrangement, Periods are arranged in a horizontal manner whereas Groups are vertically arranged on the periodic table.

Mendeleyev during the time of arranging left a few rows empty in the impression that there would be some other elements entering in the near future. And surprisingly, one of the elements that fitted in that gap was Gallium.  


Comparison Table Between Period and Group (in Tabular Form)

Parameter of Comparison




Periods are the horizontal rows on the modern periodic table

Groups are the vertical columns that runs through the top on the periodic table


The elements in a period do not have similar properties.

The elements in each group have some similar properties, but not entirely identical properties.


Elements in the same period has equal number of electron composition

Elements in each group have an equal number of valence electrons


There are 7 periods on the periodic table

The group contains 18 elements arranged vertically in modern periodic table


It increases from left to right.

It increases from bottom to top in a group.


What is Period?

A period is a horizontal row that goes from extreme left to the far right on the periodic table. As of now, there are 7 periods on the periodic table.  A new period begins when a fresh fundamental energy level adds up with the electrons. Every element in a period is likely to have an equal number of atomic orbitals. 

For example – every element in the 1st period has only 1 orbital for its own electrons, 2nd period includes 2 orbitals for the electrons. Similarly, as you move down in the row, orbitals keep adding up.

The size of the element decreases as you move across a period as the number of electron shells remains constant across the period but the number of protons rises in the nucleus. This is the reason why the atom gets heavier but the size keeps on decreasing.

Looking at the periodic table, you would see there are different elements fitted in each row.

The 1st period has only 2 elements (1 & 18), the 2nd and 3rd period have 8 elements each, the 4th and 5th period have 18 elements and lastly, the 6th and 7th period have 32 elements each respectively.


What is Group?

When you count from top to bottom there are a total of 18 groups in the periodic table. All the groups are allotted with distinct names.  

The groups are mixed categories of metals, non-metals, and semi-metals which are grouped into families according to their similar properties. Eg., Group 1 belongs to the Lithium family classified as Alkene metals. Similarly, each group in the lane has its own family name.

Elements in the related group have similar traits because they have the same electron counts in their outermost shell. The size of the element increases as you move downwards any group. This is because there are large numbers of protons and neutrons existing in the nucleus. On top of this, an extra electron shell is which makes the atom heavier.

For groups, there are two different ways to illustrate the elements. Having a understanding of both the numbering system is important because the periodic table appears in both the formats.

In the United States, they used letters A&B to indicate each element in the group but unfortunately, it was observed as a disorganized numbering system.

In order to eliminate all possible confusion, the International Union of Pure and Applied Chemistry (IUPAC) Came up with an idea of numbering the elements as (1,2, 3… 18). However, both the numbering systems are acceptable. But IUPAC’s numbering looks simple and well-organized.

Main Differences Between Period and Group

  1. Location: Groups are the upright column whereas Periods are the straight rows in the periodic table.
  2. Number: There are total 18 number of groups and 7 periods in the periodic table among which the groups are categorized under different families and metal types.
  3. Chemical properties: All the elements in the group have analogous chemical or physical properties, whereas periods share the same electron hierarchy.
  4. Energy Level: As we go down the group from top to bottom, the energy level of electron increases. On the other hand, in each period the energy level of the electron remains the same.
  5. Electronegativity: This declines from top to bottom in a group and rises from left to right in a period. This is an important consideration while studying the periodic table.



Groups and Periods are the two ways to categorize the chemically organic or inorganic elements or metals present in the modern periodic table and the key difference between group and period is its location in the periodic table. As you now know, periods are on the horizontal line and groups are on the vertical line.


  1. https://www.naxosaudiobooks.com/booklets/0245_The_Periodic_Table.pdf
  2. https://www.technology.matthey.com/wp-content/uploads/pdf/207-266-pmr-oct08.pdf#page=43