What is the Difference Between Periods and Groups

The periodic table is a chart that organizes all the chemical elements. The elements are arranged in rows and columns. Columns are called groups, while rows are called periods. The arrangement of elements in groups and periods helps determine their physical and chemical properties to a certain extent.

What is the difference between periods and groups? Periods are the horizontal rows of the periodic table, whereas groups are the vertical columns of the periodic table.

Key Areas Covered

1. What are Periods  
      – Definition, Features 
2. What are Groups
      – Definition, Features 
3. Similarities Between Periods and Groups
      – Outline of Common Features
4. Difference Between Periods and Groups
      – Comparison of Key Differences
5. FAQ: Periods and Groups
      – Answers to Frequently Asked Questions

Key Terms

Periods, Groups, Periodic Table

What are Periods

Periods are the horizontal rows of the periodic table. Each period signifies a new layer, or energy level, available for electrons to occupy. From left to right across a period, the number of protons in an element’s nucleus increases by one. This attracts one more electron, which typically fills the outermost energy level.

The number of elements in a period is dictated by the capacity of this outermost shell. The first period, with only two elements (hydrogen and helium), has its electrons confined to the first energy level. Periods 2 and 3 can accommodate eight electrons each, while periods 4 and 5 hold up to 18. The longer periods 6 and 7 (including the two separate rows at the bottom) have even more complex electron arrangements due to the filling of additional sub-shells within the outermost level.

Elements within a period have the same number of energy levels. When moving from left to right across a period, the number of protons increases one by one. Due to this increase in proton number, the elements possess different chemical characteristics. The elements on the left side of the period (metals) tend to lose electrons, while elements on the right side (non metals) tend to gain more electrons.

Furthermore, periods in the periodic table can be used to understand the electronic configuration and predicting trends in properties of elements.

What are Groups

Groups refer to the vertical columns that is seen in the periodic table. Elements with similar characteristics are seen within groups, due to their electronic configuration of the outer most energy level. Elements within a group have same number of electrons in the outermost energy level called valency shell.

For example, all the alkali metals (Group 1) are highly reactive and readily lose one electron to form a positive ion (cation).

There are 18 groups in total, numbered from 1 to 18. Here are some of the common group names:

• Group 1: Alkali metals
• Group 2: Alkaline earth metals
• Group 17: Halogens

Certain chemical and physical properties of certain elements within the same group, when going down the group changes due to the increase in the energy levels. For example, in group 17(halogens), reactivity decreases down the group.

By studying the pattern of arrangement of elements in the group, we can predict the chemical and physical properties of elements.

Similarities Between Periods and Groups

1. Both periods and groups help categorize elements based on their properties.
2. Elements within a period or group often exhibit trends in their properties.

Difference Between Periods and Groups

Definition

• Periods are horizontal rows in the periodic table, while groups are vertical columns in the periodic table.

Nature

• Elements within a period have the same highest principal energy level, while elements within a group share the same number of valence electrons.

Number of Elements

• Periods typically have a variable number of elements, with the first period having only 2 elements and subsequent periods having up to 32 elements. Groups generally have a more consistent number of elements (usually 8 or 18).

Number

• The modern periodic table has 18 groups and 7 periods.

Properties

• As you move from left to right across a period, the properties of elements gradually change. For example, atomic radius decreases, ionization energy increases, and electronegativity increases. Elements within the same group have similar chemical and physical properties. This is because they have the same number of valence electrons.

Conclusion

Periods are horizontal rows, while groups are vertical columns in a periodic table. Periods signify the number of electron shells (energy levels), while groups represent the number of valence electrons (outermost shell). This is the main difference between periods and groups. These groups and periods could be used to identify the patterns of chemical and physical properties of elements.

FAQ: Periods and Groups

1. How do you know what period and group an element is in?

There are two main ways to identify the period and group of an element on the periodic table. One is by using the electronic configuration. The other way is by referring to the periodic table. The period number is equal to the number of electron shells in the atom, while the group number is determined by the number of valence electrons (electrons in the outermost shell).

2. How many periods and groups are in a periodic table?

The modern periodic table has 18 groups (vertical columns) and 7 periods (horizontal rows).  The first period has only 2 elements and subsequent periods has up to 32 elements. Groups generally have a more consistent number of elements (usually 8 or 18).

3. How is a group different from a period?

Groups are vertical columns and represent elements with similar valence electron configurations. Periods are horizontal rows and represent elements with the same number of electron shells. The number of electron shells corresponds to the period number.

4. What are the 7 groups of the periodic table?

The 7 groups of the periodic table include:

1. The Alkali Metals
2. The Alkaline Earth Metals
3. The Transition Metals
4. The Non-metals
5. The Halogens
6. The Noble Gases
7. The Rare Earth Elements

5. What group is the most reactive?

There are two types of groups which are most reactive. They are the halogens (which is the group 17) and alkali metals (which is the group 1).

Reference:

1. “Group (periodic table).” Wikipedia. Wikipedia Foundation.
2. “Periodic Table.” Encyclopedia Britannica.

Image Courtesy:

1. “Periodic table detailed v1” By Adrianrorheim – Own work (CC BY-SA 4.0) via Commons Wikimedia