Skip to content
Related Articles

Related Articles

Improve Article
Save Article
Like Article

Characteristics of the Periods and Groups of the Periodic Table

  • Last Updated : 08 Dec, 2021

The physical and chemical properties of elements in the modern periodic table exhibit a consistent variation throughout periods and groups. Several properties of elements, such as the number of valence electrons, valency, atom size, and metallic character, vary as you move from left to right in a period. These qualities change as you move from the top to the bottom of a group. These properties of periodic table elements are discussed in further detail below.

What is a Modern Periodic Table?

The present periodic table is said to have been invented by Bohr. It’s also known as the periodic table in its larger form. The elements are organised in ascending atomic number order in horizontal rows termed periods in the modern table. Other elements with the same number of valence electrons are grouped underneath each element so that all elements with the same number of valence electrons are in the same vertical column, known as a group.

The modern periodic table arranges the elements according to their atomic numbers. “The properties of elements are a periodic function of their atomic numbers,” according to the modern periodic law. This means that elements with the same properties will occur at regular intervals or periods if atoms are organised in tabular form by increasing atomic numbers. 

The electronic configurations of elements show regular periodicity when atoms are organised by increasing atomic numbers. Periodicity in element electrical configurations leads to periodicity in element chemical properties. Electronic configurations are similar among elements with similar chemical properties.

  • Periods– Periods are the horizontal rows of elements in a periodic table. There are seven periods in the periodic table. The atomic numbers of the elements in the periodic table are consecutive. The number of elements in each time varies. The number of elements in a period is determined by the maximum number of electrons that may be accommodated in an atom’s various shells.
  • Groups– Groups are the vertical columns in a periodic table. In the long form of the periodic table, there are 18 groups. The elements in a group do not have the same atomic number. Group 1 is on the left side of the periodic table, whereas group 18 is on the right.

Characteristics of Periods in a Periodic Table

Moving from left to right in a period of the periodic table, that is, moving from left to right in a horizontal row of the periodic table, we will discuss the variation of some of the important properties of elements including the number of valence electrons, valency, atom size, and metallic character. These variations will be explained further below.

Valence Electrons 

The number of valence electrons in elements increases from 1 to 8 as a period progresses from left to right, while it increases from 1 to 2 in the first period. 

The element sodium (Na) contains one valence electron in the third period, whereas the element argon (Ar) has eight valence electrons. Every period’s first element has one valence electron and every period’s last element has eight valence electrons, with the exception of the first period, where the last element, helium (He), has only two valence electrons. 

The number of electrons in the outermost shell of an atom grows from 1 to 8 as the electronic configurations of elements vary over time. Along the period, the number of valence electrons increases from 1 to 8. The atomic numbers of the elements in a period are also consecutive. For instance, elements of the third period, from sodium to argon, have atomic numbers ranging from 11 to 18.

Elements of the third periodNaMgAlSiPSClAr
Electronic configurations2, 8, 12, 8, 22, 8, 32, 8, 42, 8, 52, 8, 62, 8, 72, 8, 8
Number of valence electrons12345678

Valency

The valency of elements increases from 1 to 4 and eventually decreases to zero as you move from left to right in a period. 

Sodium has a valency of 1, magnesium has a valency of 2, aluminium has a valency of 3, silicon has a valency of 4, phosphorous has a valency of 3, sulphur has a valency of 2, chlorine has a valency of 1, and argon has a valency of 0 in the third period. Valency increases from 1 to 4 and then decreases to zero over a period from left to right. The valency increases from 1 in sodium to 4 in silicon in the third period of the periodic table, then decreases to zero in argon. As a result, the valencies of elements from the same period differ. The valency of an element is determined by the number of electrons lost, gained, or shared by one atom to attain the nearest inert gas electron configuration.

Elements of the third periodNaMgAlSiPSClAr
Electronic configurations2, 8, 12, 8, 22, 8, 32, 8, 42, 8, 52, 8, 62, 8, 72, 8, 8
Valency12343210

Size of atoms

In a period, the atomic size decreases from left to right. The number of protons and electrons increases over time as the atomic number increases, therefore the extra electrons are added to the same shell. The electrons are drawn in closer to the nucleus due to the strong positive charge on the nucleus, and the atom’s size shrinks. As a result, there is a stronger attraction to the nucleus. Hence, the atomic size shrinks. 

Thus, in any period, the alkali metal atoms (lithium, sodium, potassium, etc.) at the far left of the periodic table are the largest, while the halogen atoms (fluorine, chlorine, bromine, etc.) at the far right of the periodic table, excluding inert gas, are the smallest. However,  inert gas’s atom, on the other hand, is larger than the halogen atom preceding it.

Metallic Character

The metallic character of elements decreases as you move from left to right, while the non-metallic character increases. Metals in the third period include sodium, magnesium, and aluminium. Silicon has properties that fall in between metals and non-metals, making it a metalloid. Phosphorus, sulphur, and chlorine are non-metallic elements. 

The components on the extreme left side of a period have the most metallic character, whereas the elements on the extreme right side of a period have the most non-metallic character. Metals are known as electropositive elements because they lose electrons and generate positive ions. 

Non-metals, on the other hand, receive electrons and create negative ions, giving them the name electronegative elements. The atomic size shrinks from left to right over time as the nuclear force of attraction increases. As a result, losing valence electrons is difficult. Hence, metals’ electropositivity decreases over time. A non-metal atom can also easily gain electrons. 

As a result, the electronegativity of non-metals increases over time. As a result, sodium is the most electropositive element in the third period, whereas chlorine is the most electronegative.

Elements of the third periodNaMgAl      SiPSCl
Nature of elementsMetalsMetalloidNon-metals

Characteristics of Groups in a Periodic Table

Moving from top to bottom in a group of the periodic table, that is, moving from top to bottom in a vertical column of the periodic table, we will discuss the variation of some of the important properties of elements including the number of valence electrons, valency, atom size, and metallic character. These variances will be explained further below.

Valence Electrons

Each element in a periodic table group has the same number of valence electrons. Lithium, sodium, and potassium, for example, all contain one valence electron in their atoms and belong to group 1 of the periodic table. Lithium, sodium, and potassium atoms can easily lose their one valence electron to create potassium ions with one unit positive charge, Li, Na, and K, respectively. 

As a result, group 1 elements are monovalent with a valency of 1. In their atoms, all elements in group 2 have two valence electrons. Except for helium, which has only two valence electrons in its atom, group 13 elements have three valence elements, group 14 elements have four valence electrons, group 15 elements have five valence electrons, group 16 elements have six valence electrons, group 17 elements have seven valence electrons, and group 18 elements have eight valence electrons. As a result, as you move down the periodic table, the number of valence electrons in the elements stays the same.

Valency

All elements in a group have the same valency because the number of valence electrons that determine valency is the same. Lithium, sodium, and potassium, for example, all have one valence electron, hence all the elements in group 1 have the same valency of one. 

Group 1 elements have a valency of 1, group 2 elements have a valency of 2, group 13 elements have a valency of 3, group 14 elements have a valency of 4, group 15 elements have a valency of 3, group 16 elements have a valency of 2, group 17 elements have a valency of 1, and group 18 elements have a valency of 0. As a result, each group’s valency is the same.

Size of atoms

The size of atoms or atomic size grows as one moves down a group of the periodic table. When we proceed down in group 1 from top to bottom, the size of the atoms gradually increases from lithium to francium. Every time we proceed from the top to the bottom of a group, a new shell of electrons is added to the atoms. 

As a result, the number of electron shells in the atoms steadily increases, causing the atoms’ size to increase as well. So, the lowest atomic size may be found at the top of the group, while the biggest atomic size can be found at the bottom. For example, in group 1, lithium (Li) is the smallest element, whereas francium (Fr) is the largest element.

LiSmallest atom
Na

Atomic size increases 

on going down the group

K
Rb
Cs
FrBiggest atom

Metallic Character

The metallic character of elements increases as you move from top to bottom, while the non-metallic character decreases. The elements in the bottom half of the group have the most metallic character. For instance, the metallic nature of group 1 increases from lithium to francium. Every time we move down a group of the periodic table, one more electron shell is added, and the size of the atoms grows. 

The valence electrons move further away from the nucleus, and the nucleus’ hold on valence electrons weakens. As a result, the atom can lose valence electrons more quickly and create positive ions, increasing its electropositivity. Furthermore, as the size of atoms grows larger as they progress through the group, the nucleus becomes more embedded in the atom. The nucleus’ attraction to the incoming electron decreases, making it difficult for the atom to create negative ions and reducing electronegative characteristics.

Sample Questions

Question 1: Which element has the largest size in the third period?

Answer: 

In a period, the atomic size decreases from left to right. This indicates that the element to the left of the period is the largest, while the element to the right of the period is the smallest. The element on the left in the third period is sodium, hence sodium (Na) has the largest size in the third period.

Question 2: What is the tendency to lose electrons over a period?

Answer: 

The nuclear charge grows as the number of protons increases over a period, and the valence electrons are drawn in more strongly by the nucleus, making it more difficult for the atoms to lose electrons. As a result, as a period progresses from left to right, the tendency of atoms to lose electrons decreases.

Question 3: What are the usual valence electrons and valency of the elements of group 2?

Answer:

The elements of group 2 are beryllium, magnesium, calcium, strontium, barium, radium. All these elements have electrons in their outermost shell, so the valence electrons of the elements of group 2 are 2. Since there are two valence electrons,m so these elements can easily lose 2 electrons, hence the valency of the elements of group 2 is 2.

Question 4: An element belongs to group 2 of the periodic table, is this element metal or non-metal?

Answer:

The metallic character of elements decreases as you move from left to right in a period. The components on the extreme left side of a period have the most metallic character. Since the elements of group 2 are on the left side of the table, so the given element is a metal.

Question 5: Element A has atomic number 4, and element B has atomic number 8, and element C has atomic number 12. Which of these elements is a member of the same group?

Answer:

The number of valence electrons of elements in the group are the same.

Elements

Atomic Number

Electronic configuration

A

           4

               2, 2

B

           8

               2, 6

C

          12

               2, 8, 2

Clearly, elements A and C have 2 valence electrons. Hence they belong to the same group.


My Personal Notes arrow_drop_up
Recommended Articles
Page :

Start Your Coding Journey Now!