## Note on Electronic Configuration and Atomic Structure

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#### Electric configuration

The distribution of electrons in the various shells of an atom is known as the electron configuration. The following table shows the electronic configuration of some atoms.

Table 2: Electric configuration of atoms of some elements

 Elements Symbol Atomic number Energy shells and number of electrons in them K(1) L(2) M(3) N(4) Hydrogen H 1 1 Helium He 2 2 Lithium Li 3 2 1 Beryllium Be 4 2 2 Boron B 5 2 3 Carbon C 6 2 4 Nitrogen N 7 2 5 Oxygen O 8 2 6 Fluorine F 9 2 7 Neon Ne 10 2 8 Sodium Na 11 2 8 1 Magnesium Mg 12 2 8 2 Aluminum Al 13 2 8 3 Silicon Si 14 2 8 4 Phosphorous P 15 2 8 5 Sulfur S 16 2 8 6 Chlorine Cl 17 2 8 7 Argon A r 18 2 8 8 Potassium K 19 2 8 8 1 Calcium Ca 20 2 8 8 2

How to draw the atomic structure of an atom?
To draw the atomic structure of hydrogen atom:

1. Draw a small circle. Write 1P and 0 N. This represent nucleus.
2. Draw another circle outside the inner circle. Since, the atom of hydrogen element contains 1 proton, the number of an electron will be the same. Therefore, write e or Q the outer circle. This cell is k shell.

The atomic structure of some or the element are shown as follow:

##### Hydrogen

The atomic number of hydrogen is 1 and its mass number is also 1.

Number of electrons = Atomic number = 1

Number of protons = Atomic number = 1

Number of neutrons = Mass number - Atomic number

Thus, the hydrogen atom contains only one proton in its nucleus at high speed in the lowest energy level.

 shell K L M N no. of electrons 1 0 0 0
##### Helium

Mass no. = 4

Atomic Number = 2

Proton = 2

Neutron = 2

Electron = 2

The atomic number of helium is 2 and its mass number is 4. Therefore, it contains 2 electrons, 2 protons, and 2 neutrons.

 shell K L M N no. of electrons 2 0 0 0
##### Lithium

Mass no. = 7

Atomic no. = 3

Proton = 3

Neutron = 4

Electrons = 3

 shell K L M N no. of electrons 2 1 0 0
##### Beryllium

Mass no. = 9

Atomic no. = 4

Proton = 4

Neutron = 5

Electron = 2, 2

 shell K L M N no. of electrons 2 2 0 0
##### Boron

Mass no. = 11

Atomic no. = 5

Proton = 5

Neutron = 6

Electron = 2, 3

 shell K L M N no. of electrons 2 3 0 0
##### Carbon

Mass no. = 12
Atomic no = 6
Proton = 6
Neutron = 6
Electron = 2, 4

The atomic weight of carbon is 6 and its mass is 12. Therefore, it contains 6 electrons, 6 protons, and 6 neutrons.

 shell K L M N no. of electrons 2 4 0 0

• The distribution of electrons in the various shells of atom is known as the electron configuration.
• Draw a small circle. Write 1P and 0 N. This represent nucleus.
• Draw another circle outside the inner circle. Since, the atom of hydrogen element contain 1 proton, the number of electron will be the same. Therefore, write e or Q the outer circle. This cell is k shell.
• Likewise there are higher shells such as L, M, N which hold different number of electrons.
.

### Very Short Questions

The molecule is the smallest particle which possesses the properties of a compound.

The 2n2 rule is a rule which is used to determine the number of electrons that can exist different shell of atoms. For example: for k shell (n)= 1
No of electron in k-shell = 2n2
= 2 (1)2
=2
No of electron in L-shell = 2n2
2.(2)2
2 x 4
=8

The tendency of an atom to have 8 electrons in their outermost shell is called octet. The tendency of an atom to have two electrons in their first shell is called duplet.

Those elements which can react easily with other elements during chemical reactions are called reactive elements.

Neon is an inert gas because its outermost orbit is fulfilled with 8 electron and it does not take part in chemical reaction.

The valency of oxygen is two because it gains two electrons during the chemical reaction.

The elements of group IA are called alkali metals because they easily react with water to produce alkali.

Chlorine is called reactive non-metals because it can easily gain one electron and possesses unit negative charge.

0%

2

4

3

5

• ### The energy of the shell ______ as we move away from the nucleus.

does not change

cannot be predicted because it depends of individual atom

increases

decreases

8

2

16

18

• ### The process of distribution of electrons in the various shell of the atom is called _______.

electron distribution

electronic configuration

valency

electron assimilation

• ### Which one of the following is correct?

Number of electrons = Mass number - Atomic number

Number of neutrons = Mass number - Atomic number

Number of neutrons = Mass number + Atomic number

Number of protons = Mass number - Atomic number

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