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Electronic configuration of first 30 elements - Rules of writing electronic configuration, examples, practice problems & FAQs

If you have 30 elements and task to arrange them according to their similar chemical and physical properties, on the basis of which property you try to arrange them?

Electronic configurations tell us about their outermost electronic configuration (valence electrons), we can easily arrange them to their similar chemical and physical property. 

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Table of contents

  • What is electronic configuration?
  • Aufbau’s principle
  • Pauli’s Exclusion Principle
  • Hund’s rule for maximum multiplicity
  • Exceptional electronic configurations
  • Electronic configurations of elements from atomic number 1 to 30 (H to Zn)
  • Condensed electronic configuration
  • Application of electronic configuration:
  • Practice Problems
  • Frequently Asked Questions-FAQs

What is electronic configuration?

Electrons are filled in orbitals of an element under a set of rules based on the parameters of energy, indistinguishability and orientation.

Rules for Filling Electrons in Orbitals

  • Aufbau's principle
  • Pauli’s exclusion principle
  • Hund’s rule for maximum multiplicity

Aufbau’s principle

Electrons are filled in various orbitals in order of their increasing energies. Orbitals having the lowest energy are filled first. The order in which orbitals increase in energy is called the orbital sequence.

  • Energies of subshells of single-electron species

Note: Energy of single-electron species depends only on the principal quantum number (n).

Order of Energy, 1s < 2s = 2p < 3s = 3p = 3d < 4s = 4p = 4d = 4f < …

image

  • Energies of subshells of multi-electron species

Note: Energy of single-electron species depends on the principal quantum number (n) & azimuthal quantum number (l).

The energy of orbitals depends on (n+l) rule.

Letter code (subshell)

Value of l

0

p

1

d

2

f

3

 

Subshell

Value of l

Value of n

(n+l)

1s 

0

1

1

2s

0

2

2

2p

1

2

3

3s

0

3

3

Note: if two subshells with same (n+l) value, subshell with lower ‘n’ value has lower energy

Order of Energy, 1s < 2s < 2p < 3s < 3p < 3d < 4s < 4p < 4d < 4f < …

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  • Memory Map for writing Electronic Configuration

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Pauli’s Exclusion Principle

No two electrons in an atom can have the same set of all four quantum numbers.

image

Hund’s rule of maximum multiplicity 

No electron pairing takes place in the orbitals in a sub-shell until each orbital is occupied by one electron with parallel spin. Exactly half-filled and fully filled orbitals make the atoms more stable, i.e., p3, p6, d5,d10,f7&f14 the configuration is most stable. 

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Maximum spin multiplicity = 2|S|+1

|S| = Modulus of the maximum spin of an atom

Exceptional electronic configurations:

image

Electronic configurations of elements from atomic number 1 to 30 (H to Zn)

Name of element

Symbol

Atomic number

Electronic configuration

Hydrogen

H

1

H1- 1s1

Helium

He

2

He2- 1s2

Lithium

Li

3

Li3- 1s2,2s1

Berillium 

Be

4

Be4- 1s2,2s2

Boron

B

5

B5- 1s2,2s22p1

Carbon

C

6

C6- 1s2,2s22p2

Nitrogen

N

7

N7- 1s2,2s22p3

Oxygen

O

8

O8- 1s2,2s22p4

Flourine

F

9

F9- 1s2,2s22p5

Neon

Ne

10

Ne10- 1s2,2s22p6

Sodium

Na

11

Na11- 1s2,2s22p6,3s1

magnesium

Mg

12

Mg12- 1s2,2s22p6,3s2

Aluminium

Al

13

Al13- 1s2,2s22p6,3s23p1

Silicon

Si

14

Si14- 1s2,2s22p6,3s23p2

Phosphorous 

P

15

P15- 1s2,2s22p6,3s23p3

Sulphur

S

16

S16- 1s2,2s22p6,3s23p4

Chlorine

Cl

17

Cl17- 1s2,2s22p6,3s23p5

Argon

Ar

18

Ar18- 1s2,2s22p6,3s23p6

Potassium

K

19

K19- 1s2,2s22p6,3s23p6,4s1

Calcium 

Ca

20

Ca20- 1s2,2s22p6,3s23p6,4s2

Scandium

Sc

21

Sc21- 1s2,2s22p6,3s23p63d1,4s2 or

1s2,2s22p6,3s23p6,4s2,3d1

Titanium

Ti

22

Ti22- 1s2,2s22p6,3s23p63d2,4s2 or 1s2,2s22p6,3s23p6,4s2,3d2

Vanadium

V

23

V23- 1s2,2s22p6,3s23p63d3,4s2 or 1s2,2s22p6,3s23p6,4s2,3d3

Chromium

Cr

24

Cr24- 1s2,2s22p6,3s23p63d5,4s1 or 1s2,2s22p6,3s23p6,4s1,3d5

Manganese

Mn

25

Mn25- 1s2,2s22p6,3s23p63d5,4s2 or 1s2,2s22p6,3s23p6,4s2,3d5

Iron

Fe

26

Fe26- 1s2,2s22p6,3s23p63d6,4s2 or 1s2,2s22p6,3s23p6,4s2,3d6

Cobalt

Co

27

Co27- 1s2,2s22p6,3s23p63d7,4s2 or 1s2,2s22p6,3s23p6,4s2,3d7

Nickel

Ni

28

Ni28- 1s2,2s22p6,3s23p63d8,4s2 or 1s2,2s22p6,3s23p6,4s2,3d8

Copper

Cu

29

Cu29- 1s2,2s22p6,3s23p63d10,4s1 or 1s2,2s22p6,3s23p6,4s1,3d10

Zinc

Zn

30

Zn30- 1s2,2s22p6,3s23p63d10,4s2 or 1s2,2s22p6,3s23p6,4s2,3d10

Condensed electronic configuration

Rules to write condensed electronic configuration or noble gas configuration

  • Electrons are filled in valence or outermost shell according to given order

(n-2)f0-14(n-1)d0-10ns0-2np0-6

where, n outermost (valence) shell

 (n-1) penultimate shell

 (n-2) anti-penultimate shell

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Example: Write the condensed electronic configuration of flerovium (Fl114).

Answer: We know, the last element of period 6 is Rn86.

114-86 = 28, only we have arranged 28 electrons in their valence, penultimate & anti-penultimate shells according to increasing (n+l) rule

This element belongs to period 7 because period 6 is completely filled and the last element of period 7 is

Og118. So, n = 7, (n-1) =6 and (n-2) =5

Subshell

n

l

(n+l)

Preference Rank

Maximum capacity of electron

Actual number of electrons

7s

7

0

7

1

2

2

7p

7

1

8

4

6

2

6d

6

2

8

3

10

10

5f

5

3

8

2

14

14

Note: subshells having same (n+l) value, subshell with the lower value of n is preferred

image

Condensed electronic configurations of elements

H1- 1s1

He2- 1s2

Li3- [He] 2s1

Be4- [He] 2s2

B5- [He] 2s22p1

C6- [He] 2s22p2

N7- [He] 2s22p3

O8- [He] 2s22p4

F9- [He] 2s22p5

Ne10- [He] 2s22p6

Na11- [Ne] 3s1

Mg12- [Ne] 3s2

Al13- [Ne] 3s23p1

Si14- [Ne] 3s23p2

P15- [Ne] 3s23p3

S16- [Ne] 3s23p4

Cl17- [Ne] 3s23p5

Ar18- [Ne] 3s23p6

K19- [Ar] 4s1

Ca20- [Ar] 4s2

Sc21- [Ar] 3d1,4s2 or [Ar] 4s2,3d1

Ti22- [Ar] 3d2,4s2 or [Ar] 4s2,3d2

V23- [Ar] 3d3,4s2 or [Ar] 4s2,3d3

Cr24- [Ar] 3d5,4s1 or [Ar] 4s1,3d5

Mn25- [Ar] 3d5,4s2 or [Ar] 4s2,3d5

Fe26- [Ar] 3d6,4s2 or [Ar] 4s2,3d6

Co27- [Ar] 3d7,4s2 or [Ar] 4s2,3d7

Ni28- [Ar] 3d8,4s2 or [Ar] 4s2,3d8

Cu29- [Ar] 3d10,4s1 or [Ar] 4s1,3d10

Zn30- [Ar] 3d10,4s2 or [Ar] 4s2,3d10

Application of electronic configuration:

A. Identification of color of metallic ions compounds
Compounds generally exhibits colours due to excitation and deexcitation of electrons. In compounds of d block elements colors are produced by mainly 2 reasons

  • d-d transition
  • Charge transfer

The energy of excitation relates to the frequency of light absorbed when an electron from a lower energy d orbital is pushed to a higher energy d orbital. This frequency is usually in the visible range. The colour seen matches the light absorbed's complementary colour.

  • Generally, ions having configurations d0 & d10 are colorless and configuration d1 to d9 exhibit colours. (in KMnO4 , K2Cr2O7 Mn and Cr both have d0 configuration but they exhibit colour due to charge transfer, not due to d-d transition.)
  • Magnetic behaviour 

Case 1: if unpaired electrons are present then, the ion exhibits paramagnetic behaviour.

Case 2: if all electrons are fully paired then, the ion exhibits paramagnetic behaviour.

Case 3: if half-filled subshells are present, the ion exhibits ferromagnetic behaviour (d5- extreme case of paramagnetism).

  • Spin magnetic moment

With the help of electronic configuration we can easily find its spin magnetic moment,

 image

n=number of unpaired electron

Example 1: Find the spin magnetic moment of d6 configuration?

Answer: dconfiguration :

image

 number of unpaired electron = 4

image

  • Maximum spin multiplicity:

Maximum spin multiplicity = 2|S|+1 

S = total spin 

E.g- for d6 configuration 

image

  • Exchange energy

Electrons having the same spin and energy present in degenerate orbitals can exchange their positions and in this exchange process, the energy is released and the released energy is termed exchange energy. 

The higher the number of exchanges in a particular configuration, the stability of the configuration becomes higher.

The exchange energy is the basis for Hund's rule, which allows maximum multiplicity, that is electron pairing is possible only when all the degenerate orbitals contain one electron each.

more the number of exchange ∝ more the stability of configuration

=maximum number of possible exchangeimage

Where n is the total number of electrons having same energy and spin

r = 2 (minimum 2 electrons required for exchange)

E.g- for d8 configuration 

d8 configuration:

image

Case 1:

image

Number of electrons having same energy and spin (n) = 5

Minimum number of electrons required for exchange = 2

 image

Case 2: 

image

Number of electrons having same energy and spin (n) = 3

Minimum number of electrons required for exchange = 2

 image

Total number of possible exchange = 10 + 3 = 13

  • Chemical properties

We can categorize elements having same chemical properties on the basis of their same outer electronic configuration.

E.g: Li3- 1s2,2s1

Na11- 1s2,2s22p6,3s1

K19- 1s2,2s22p6,3s23p6,4s1

Li, Na, K have same outermost electronic conjugation ns1

F9- 1s2,2s22p5 and Cl17- 1s2,2s22p6,3s23p5 have same chemical behaviour both have same outer electronic configuration ns2np5

  • To predict the group number, period number and block name of elements according to modern periodic table

Rules to identify group number, period number & block name of elements

  • Period number: Value of n (principal quantum number) of valence shell or outermost shell decide the number of period of element

Eg. F9 [He],2s22p5; n=2 - belongs to 2nd the period of periodic table

Na11 [Ne]3s1; n=3 - belongs to 3rd the period of periodic table

  • Block name: The last electron enters in which subshell, elements generally belongs to that block

Eg. 

F9 [He],2s22p5; the last electron enters in p a subshell. So, Fluorine is a p block element

Na11 [Ne]3s1; the last electron enters in s a subshell. So, Sodium is a s block element

  • Group number: Generally, the group number is decided by the number of valence electrons or valence electrons and electrons of the penultimate shell.
  1. For s block elements- the group number is equal to the number of valence electrons(n).
  2. For p block elements- the group number is equal to the number of valence electrons (n)+ 10.
  3. For d block elements- the group number is equal to the number of valence electrons(n) + number of electrons in the penultimate shell (n-1) d orbital.

E.g

F9image [He],2s22p5; p block elements. So, Group no = 7 + 10 = 17

Na11image [Ne]3s1; s block elements. So, Group no = 1 

Fe26image1s2,2s22p6,3s23p63d6,4s2; d block elements. So, Group no = 6 + 2 = 8 

Video link: 

Practice problems:

Q1. Find the spin magnetic moment of manganese (Mn25)

image
Answer: (A)

Solution: 

Electronic configuration of Mn = Mn25- [Ar] 3d5,4s2 or [Ar] 4s2,3d5

image

 number of unpaired electron = 5

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Q2. Which ion in their aqueous solution exhibit colour

A. Ti3+
B. Sc3+
C. Cu+
D. Zn2+

Answer: (A)

Solution: 

Due to d-d transition generally ions having electronic configuration d1 to d9 exhibit colour and d0 to d10 are colourless.

 Ti-[Ar] 3d24s2 and Ti3+-[Ar] 3d1, number of unpaired electron = 1 & it exhibit colour.

Sc-[Ar] 3d14s2 and Sc3+-[Ar] 3d0, number of unpaired electrons = 0 & it doesn’t exhibit colour.

Cu-[Ar] 3d104s1 and Cu+-[Ar] 3d104s0, number of unpaired electrons = 0 & it doesn’t exhibit colour.

Zn-[Ar] 3d104s2 and Zn2+-[Ar] 3d104s0, number of unpaired electrons = 0 & it doesn’t exhibit colour.

Q3. Condensed electronic configuration of F is 

A. 1s2,2s22p5
B. [He] 2s22p5
C. K - 2, L - 7
D. All of these

Answer: (B)

Condensed electronic configuration of F is [He] 2s22p5

Q 4. Carbon in its ground state is 

A. Monovalent
B. Divalent
C. Trivalent
D. tetravalent

Answer: (B)

Solution: electronic configuration of C is 1s2, 2s22p2

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Frequently Asked Questions-FAQs

Question 1. Can we write exactly the correct configurations of all elements by strictly following (n + l) rule, Pauli exclusion principle, and Hund's rule?
Answer: No, we can see many configurations which don’t obey these rules (specially Aufbau). Eg. Cr, Cu, Pd, Pt, etc.

Question 2. Is the outermost electronic configuration of elements along with a group of the periodic tables always the same?
Answer: Not always, we can observe in many cases,

Eg- He - 1s2 but Ne - 1s2,2s22p6

We can observe the same in many cases in transition metal series.

Question 3. Is it necessary to start filling any orbitals with an upward arrow?
Answer: No, you can start filling orbitals with upward or downward spin but make sure, no electron pairing takes place in the orbitals in a sub-shell until each orbital is occupied by one electron with parallel spin.

Question 4. What are exchange energy and pairing energy?
Answer: Exchange energy is the energy released when two or more electrons with the same spin exchange their positions in the degenerate orbitals of a subshell. The more the options for exchange, the more the electron’s stability. The number of exchange pairs is maximum in half-filled orbitals, hence it is more stable compared to partially filled orbitals.

Pairing energy refers to the energy released with paired electrons sharing one orbital. The more the paired electrons the more the atom’s stability. The number of pairs is maximum in fully filled orbitals, hence it is more stable compared to partially filled orbitals.

Related topics:

Isotopes Isobars, Isotones & Isodiaphers

Discovery of neutron

Rutherford atomic model

Thompson’s Atomic Model

Atomic number and Mass number

Quantum numbers

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