In the previous section 3.1, we completed a discussion on the relationship between the following two items:
• Electronic configuration of an element
• Period to which that element belongs
■ In this section, we will begin a discussion to study the relationship between the following two items:
• Electronic configuration of an element
• Group to which that element belongs
First we will see four important terms:
1. Valence shell
2. Valence electrons
3. Valence orbitals
4. Physical and chemical properties of elements
• Let us learn about them in detail:
1. Valence shell
• The outer most main-shell of an atom is called the valence shell of that atom
Let us see some examples:
Example 1:
We will consider an element from the s-block
• 11Na has the electronic configuration: 1s22s22p63s1
♦ We see that nh (highest principal quantum number n) = 3
♦ So the outer ‘most main-shell’ is the main-shell with n= 3 (the M shell)
♦ In other words, the 'valence shell of sodium' is the main-shell with n= 3
Example 2:
We will consider an element from the p-block
• 53I has the electronic configuration: [Ar]4s23d104p65s24d105p5
♦ We see that nh = 5
♦ So the outer ‘most main-shell’ is the main-shell with n= 5 (the O shell)
♦ In other words, the 'valence shell of iodine' is the main-shell with n= 5
• Electronic configuration of an element
• Period to which that element belongs
■ In this section, we will begin a discussion to study the relationship between the following two items:
• Electronic configuration of an element
• Group to which that element belongs
First we will see four important terms:
1. Valence shell
2. Valence electrons
3. Valence orbitals
4. Physical and chemical properties of elements
• Let us learn about them in detail:
1. Valence shell
• The outer most main-shell of an atom is called the valence shell of that atom
Let us see some examples:
Example 1:
We will consider an element from the s-block
• 11Na has the electronic configuration: 1s22s22p63s1
♦ We see that nh (highest principal quantum number n) = 3
♦ So the outer ‘most main-shell’ is the main-shell with n= 3 (the M shell)
♦ In other words, the 'valence shell of sodium' is the main-shell with n= 3
Example 2:
We will consider an element from the p-block
• 53I has the electronic configuration: [Ar]4s23d104p65s24d105p5
♦ We see that nh = 5
♦ So the outer ‘most main-shell’ is the main-shell with n= 5 (the O shell)
♦ In other words, the 'valence shell of iodine' is the main-shell with n= 5
Example 3:
We will consider an element from the d-block
• 26Fe has the electronic configuration: 1s22s22p63s23p63d64s2
♦ We see that nh = 4
♦ So the outer ‘most main-shell’ is the main-shell with n= 4 (the N shell)
♦ In other words, the 'valence shell of iron' is the main-shell with n= 4
Let us see some examples:
Example 1:
• 11Na has the electronic configuration: 1s22s22p63s1
♦ We have seen that the 'valence shell of sodium' is the main-shell with n= 3
♦ There is one electron in that main-shell
♦ This one electron is the 'valence electron of sodium'
Example 2:
• 53I has the electronic configuration: [Ar]4s23d104p65s24d105p5
♦ We have seen that the 'valence shell of iodine' is the main-shell with n= 5
♦ There are 7 electrons in that main-shell
♦ These 7 electrons are the 'valence electrons of iodine'
Example 3:
• 26Fe has the electronic configuration: 1s22s22p63s23p63d64s2
♦ We have seen that the 'valence shell of iron' is the main-shell with n= 4
♦ There are 2 electrons in that main-shell
♦ Are these two electrons the 'valence electron of iron'?
■ Let us find out:
• Iron is a transition element
• The last electrons get placed in the inner 3d orbital
• Some times, those electrons in the 3d also takes part in chemical reactions
• So in the case of transition elements, we give a more precise definition. It can be written in 3 steps:
(i) Write the electronic configuration
(ii) Separate the configuration into two parts:
♦ Electrons in the noble gas core
♦ Electrons outside the core
(iii) Electrons outside the core are the valence electrons
Let us apply the above steps to iron:
Step 1: 1s22s22p63s23p63d64s2
Step 2: [1s22s22p63s23p6] 3d64s2
This is same as: [Ar]3d64s2
Step 3: There are 8 electrons outside the core
• So the valence electrons are:
♦ The 6 electrons in the 3d orbital
♦ and the 2 electrons in the 4s orbital
• All of them may not be occupied
■ Those 'orbitals in the valence shell, which have at least one electron' are called valence orbitals
• This definition is in terms of 'valence shell'. It is applicable to s and p block elements
• In general, to include d and f blocks also, we can write a definition in terms of 'valence electrons':
■ Those 'orbitals occupied by valence electrons' are called valence orbitals
Let us see some examples:
Example 1:
• 11Na has the electronic configuration: 1s22s22p63s1
♦ We have seen that the 'valence shell of sodium' is the main-shell with n= 3
♦ There is one electron in that main-shell
♦ This one electron is the 'valence electron of sodium'
♦ This valence electron is in the 3s orbital
♦ So the valence orbital of sodium is 3s
Example 2:
• 53I has the electronic configuration: [Ar]4s23d104p65s24d105p5
♦ We have seen that the 'valence shell of iodine' is the main-shell with n= 5
♦ There are 7 electrons in that main-shell
♦ These 7 electrons are the 'valence electron of iodine'
♦ These 7 electrons occupy the 5s and 5p orbitals
♦ So the valence orbitals of iodine are 5s and 5p
Example 3:
• 26Fe has the electronic configuration: 1s22s22p63s23p63d64s2
♦ We have seen that the valence electrons of iron are:
♦ The 6 electrons in the 3d orbital and the 2 electrons in the 4s orbital
♦ So the valence orbitals of iron are 3d and 4s
• Some examples of physical properties are:
Melting point, boiling point, specific heat etc.,
• Some examples of chemical properties are:
Readiness to react with acid, readiness to react with oxygen etc.,
1. Valence shell
2. Valence electrons
3. Valence orbitals
4. Physical and chemical properties
• Out of the 4 items, we will need the last 3 for our next discussion
(ii) Write down the 'number of valence electrons' of each element in that group
• The 'number of valence electrons' will be same for all the elements
• Note:
♦ We have already seen 'how to determine the valence electrons' of any element
♦ So it is easy to write the 'number of valence electrons' of any element
Let us see some examples:
Example 1:
• We will consider a group from the s-block
(i) Consider Group 2
(ii) Write the 'number of valence electrons' of each element in Group 2
• They are shown in Table 3.1(a) below
• We see that, the 'number' is 2 for all the elements
Example 2:
• We will consider a group from the p-block
(i) Consider Group 15
(ii) Write the 'number of valence electrons' of each element in Group 15
• They are shown in Table 3.1(b) above
• We see that, the 'number' is 5 for all the elements
Example 3:
• We will consider an element from the d-block
(i) Consider Group 6
(ii) Write the 'number of valence electrons' of each element in Group 6
• They are shown in Table 3.1(c) above
• We see that, the 'number' is 6 for all the elements
(ii) Write down the 'valence orbitals' of each element in that group
• The 'valence orbitals' will be similar for all the elements
• Note:
♦ We have already seen 'how to determine the valence orbitals' of any element
Let us see some examples:
Example 1:
• We will consider a group from the s-block
(i) Consider Group 2
(ii) Write the 'valence orbitals' of each element in Group 2
• They are shown in Table 3.2(a) below:
• We see that, all the elements have the same type of 'valence orbitals'
• In other words, the 'valence orbitals' of all the elements are similar
• Note that, we cannot say: 'valence orbitals' are same
♦ Because, 2s is not same as 3s, which is not same as 4s, so on . . .
• Let us ignore the 'digits' (2, 3, 4 etc.,) for a while
♦ We get: 's' for all the elements
• So we can say: 'Valence orbitals' are similar
Example 2:
• We will consider a group from the p-block
(i) Consider Group 14
(ii) Write the 'valence orbitals' of each element in Group 14
• They are shown in Table 3.2(b) above
• We see that, all the elements have the same type of 'valence orbitals'
• In other words, the 'valence orbitals' of all the elements are similar
• Note that, we cannot say: 'valence orbitals' are same
♦ Because, 2s2p is not same as 3s3p, which is not same as 4s4p, so on . . .
• Let us ignore the 'digits' (2, 3, 4 etc.,) for a while
♦ We get: 's p' for all the elements
• So we can say: 'Valence orbitals' are similar
Example 3:
• We will consider a group from the d-block
(i) Consider Group 11
(ii) Write the 'valence orbitals' of each element in Group 11
• They are shown in Table 3.2(c) above
• We see that, all the elements have the same type of 'valence orbitals'
• In other words, the 'valence orbitals' of all the elements are similar
• Note that, we cannot say: 'valence orbitals' are same
♦ Because, 3d4s is not same as 4d5s, which is not same as 5d6s, so on . . .
• Let us ignore the 'digits' (3, 4, 5 etc.,) for a while
♦ We get: 'd s' for all the elements
• So we can say: 'Valence orbitals' are similar
Consider an example:
Let us take Group 1:
(i) All the elements in this group are soft
(ii) All the elements in this group have low melting points
(iii) All the elements in this group have low densities
• We will see more examples demonstrating the 'similarities in physical and chemical properties' in later chapters
• The comparison was based on three items:
(i) Valence electrons
(ii) Valence orbitals
(iii) Physical and chemical properties
■ We saw that, all elements belonging to a group will have:
♦ Same 'valence electrons'
♦ Similar 'valence orbitals'
♦ Similar 'physical and chemical properties'
We will consider an element from the d-block
• 26Fe has the electronic configuration: 1s22s22p63s23p63d64s2
♦ We see that nh = 4
♦ So the outer ‘most main-shell’ is the main-shell with n= 4 (the N shell)
♦ In other words, the 'valence shell of iron' is the main-shell with n= 4
2. Valence electrons
• The electrons present in the valence shell of an atom are called valence electrons of that atom
• The electrons present in the valence shell of an atom are called valence electrons of that atom
Example 1:
• 11Na has the electronic configuration: 1s22s22p63s1
♦ We have seen that the 'valence shell of sodium' is the main-shell with n= 3
♦ There is one electron in that main-shell
♦ This one electron is the 'valence electron of sodium'
Example 2:
• 53I has the electronic configuration: [Ar]4s23d104p65s24d105p5
♦ We have seen that the 'valence shell of iodine' is the main-shell with n= 5
♦ There are 7 electrons in that main-shell
♦ These 7 electrons are the 'valence electrons of iodine'
Example 3:
• 26Fe has the electronic configuration: 1s22s22p63s23p63d64s2
♦ We have seen that the 'valence shell of iron' is the main-shell with n= 4
♦ There are 2 electrons in that main-shell
♦ Are these two electrons the 'valence electron of iron'?
■ Let us find out:
• Iron is a transition element
• The last electrons get placed in the inner 3d orbital
• Some times, those electrons in the 3d also takes part in chemical reactions
• So in the case of transition elements, we give a more precise definition. It can be written in 3 steps:
(i) Write the electronic configuration
(ii) Separate the configuration into two parts:
♦ Electrons in the noble gas core
♦ Electrons outside the core
(iii) Electrons outside the core are the valence electrons
Let us apply the above steps to iron:
Step 1: 1s22s22p63s23p63d64s2
Step 2: [1s22s22p63s23p6] 3d64s2
This is same as: [Ar]3d64s2
Step 3: There are 8 electrons outside the core
• So the valence electrons are:
♦ The 6 electrons in the 3d orbital
♦ and the 2 electrons in the 4s orbital
3. Valence orbitals
• We have seen what a 'valence shell' is. There may be so many orbitals present in the valence shell
• We have seen what a 'valence shell' is. There may be so many orbitals present in the valence shell
■ Those 'orbitals in the valence shell, which have at least one electron' are called valence orbitals
• This definition is in terms of 'valence shell'. It is applicable to s and p block elements
• In general, to include d and f blocks also, we can write a definition in terms of 'valence electrons':
■ Those 'orbitals occupied by valence electrons' are called valence orbitals
Let us see some examples:
Example 1:
• 11Na has the electronic configuration: 1s22s22p63s1
♦ We have seen that the 'valence shell of sodium' is the main-shell with n= 3
♦ There is one electron in that main-shell
♦ This one electron is the 'valence electron of sodium'
♦ This valence electron is in the 3s orbital
♦ So the valence orbital of sodium is 3s
Example 2:
• 53I has the electronic configuration: [Ar]4s23d104p65s24d105p5
♦ We have seen that the 'valence shell of iodine' is the main-shell with n= 5
♦ There are 7 electrons in that main-shell
♦ These 7 electrons are the 'valence electron of iodine'
♦ These 7 electrons occupy the 5s and 5p orbitals
♦ So the valence orbitals of iodine are 5s and 5p
Example 3:
• 26Fe has the electronic configuration: 1s22s22p63s23p63d64s2
♦ We have seen that the valence electrons of iron are:
♦ The 6 electrons in the 3d orbital and the 2 electrons in the 4s orbital
♦ So the valence orbitals of iron are 3d and 4s
4. Physical and chemical properties of elements
• We have already seen about 'Physical and chemical properties of elements' in our earlier classes
• We have already seen about 'Physical and chemical properties of elements' in our earlier classes
Melting point, boiling point, specific heat etc.,
• Some examples of chemical properties are:
Readiness to react with acid, readiness to react with oxygen etc.,
So we have seen 4 items:
2. Valence electrons
3. Valence orbitals
4. Physical and chemical properties
• Out of the 4 items, we will need the last 3 for our next discussion
Here we discuss some properties of groups:
Property 1: 'Number of valence electrons' is same for all elements in a group
Let us elaborate:
(i) Consider any vertical column (group) of the periodic table
Property 1: 'Number of valence electrons' is same for all elements in a group
Let us elaborate:
(i) Consider any vertical column (group) of the periodic table
• The 'number of valence electrons' will be same for all the elements
• Note:
♦ We have already seen 'how to determine the valence electrons' of any element
♦ So it is easy to write the 'number of valence electrons' of any element
Let us see some examples:
Example 1:
• We will consider a group from the s-block
(i) Consider Group 2
(ii) Write the 'number of valence electrons' of each element in Group 2
• They are shown in Table 3.1(a) below
• We see that, the 'number' is 2 for all the elements
 |
| Table 3.1 |
• We will consider a group from the p-block
(i) Consider Group 15
(ii) Write the 'number of valence electrons' of each element in Group 15
• They are shown in Table 3.1(b) above
• We see that, the 'number' is 5 for all the elements
Example 3:
• We will consider an element from the d-block
(i) Consider Group 6
(ii) Write the 'number of valence electrons' of each element in Group 6
• They are shown in Table 3.1(c) above
• We see that, the 'number' is 6 for all the elements
Property 2: 'Valence orbitals' are similar for all elements in a group
Let us elaborate:
(i) Consider any group of the periodic table
Let us elaborate:
(i) Consider any group of the periodic table
• The 'valence orbitals' will be similar for all the elements
• Note:
♦ We have already seen 'how to determine the valence orbitals' of any element
Let us see some examples:
Example 1:
• We will consider a group from the s-block
(i) Consider Group 2
(ii) Write the 'valence orbitals' of each element in Group 2
• They are shown in Table 3.2(a) below:
 |
| Table 3.2 |
• In other words, the 'valence orbitals' of all the elements are similar
• Note that, we cannot say: 'valence orbitals' are same
♦ Because, 2s is not same as 3s, which is not same as 4s, so on . . .
• Let us ignore the 'digits' (2, 3, 4 etc.,) for a while
♦ We get: 's' for all the elements
• So we can say: 'Valence orbitals' are similar
Example 2:
• We will consider a group from the p-block
(i) Consider Group 14
(ii) Write the 'valence orbitals' of each element in Group 14
• They are shown in Table 3.2(b) above
• We see that, all the elements have the same type of 'valence orbitals'
• In other words, the 'valence orbitals' of all the elements are similar
• Note that, we cannot say: 'valence orbitals' are same
♦ Because, 2s2p is not same as 3s3p, which is not same as 4s4p, so on . . .
• Let us ignore the 'digits' (2, 3, 4 etc.,) for a while
♦ We get: 's p' for all the elements
• So we can say: 'Valence orbitals' are similar
Example 3:
• We will consider a group from the d-block
(i) Consider Group 11
(ii) Write the 'valence orbitals' of each element in Group 11
• They are shown in Table 3.2(c) above
• We see that, all the elements have the same type of 'valence orbitals'
• In other words, the 'valence orbitals' of all the elements are similar
• Note that, we cannot say: 'valence orbitals' are same
♦ Because, 3d4s is not same as 4d5s, which is not same as 5d6s, so on . . .
• Let us ignore the 'digits' (3, 4, 5 etc.,) for a while
♦ We get: 'd s' for all the elements
• So we can say: 'Valence orbitals' are similar
Property 3: Elements belonging to a group shows similar physical and chemical properties
Let us take Group 1:
(i) All the elements in this group are soft
(ii) All the elements in this group have low melting points
(iii) All the elements in this group have low densities
• We will see more examples demonstrating the 'similarities in physical and chemical properties' in later chapters
• So we have compared 'various elements' in 'various groups'
(i) Valence electrons
(ii) Valence orbitals
(iii) Physical and chemical properties
■ We saw that, all elements belonging to a group will have:
♦ Same 'valence electrons'
♦ Similar 'valence orbitals'
♦ Similar 'physical and chemical properties'
In the next section, we will see the various blocks in the periodic table
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