Question
Sun March 30, 2014

# I'M NOT ABLE TO VISUALISE HOW AN ATOM REALLY LOOKS BECAUSE ALL THESE YEARS I THOUGHT IT WAS LIKE A SOLAR SYSTEM...

Tue April 01, 2014
Dear dikishta

Thanks for asking us a question in Ask the Expert section of TopperLearning.com.

You have asked extremely intelligent question.

It is very difficult to understand all your doubts by refering only diagram of an atom. However, for your clear concept you need to understand the basic concept of atom. For this you can refer to the information provided below. Kindly go through each and every points/aspects/concepts.

An atom is defined as the basic unit of element. By basic, we mean that it is the building block of matter. It is the smallest particle of an element that can take part in a chemical reaction. Every atom consists of protons, neutrons and electrons.

Orbital - The region of space around the nucleus where the possibility of finding an electron is maximum is called an orbital.

Main shells are K, L, M, N and so on…

Sub shells are a division of main shells (K, L, M, N etc) and are composed of atomic orbitals. Example: s, p, d , f etc.

According to Bohr's model, electrons occupy certain stable orbits or shells. Each shell has definite energy.

The maximum number of electrons present in the shell is given by the formula (2n2), where n is the orbit number or shell number.

First orbit or K shell will be = 2 X 12 = 2, Second orbit or L shell will be = 2 X 22 = 8,   Third orbit or M shell will be = 2 X 32 = 18, Fourth orbit or shell will be = 2 X 42 = 32 and so on.

 Shell designation Shell number  (n) Formula 2n2 Maximum number of electrons in each shell K-shell 1 2 x (1)2 2 L-shell 2 2 x (2)2 8 M-shell 3 2 x (3)2 18 N-shell 4 2 x (4)2 32

The maximum number of electrons that can be accommodated in the outermost orbit is 8.

Each shell is composed of one or more subshells, which are themselves composed of atomic orbitals. For example, the first (K) shell has one subshell, called 1s; the second (L) shell has two subshells, called 2s and 2p; the third shell has 3s, 3p, and 3d; the fourth shell has 4s, 4p, 4d and 4f; the fifth shell has 5 s, 5 p, 5 d, and 5 f and can theoretically hold more but the 5f subshell.

Starting with the energy level/shell closest to the nucleus electrons fill the different shells in order of increasing energy.

 Shell 1 Shell 2 Shell 3 Shell 4 ------------------------------- Increasing Energy ----------------------------->

Energy levels or shells can be divided into sub-shells, which can hold different numbers of electrons.

 Shell 1 Shell 2 Shell 3 Shell 4 Sub-Shell s s p s p d s p d f

Within each sub-shell there are one or more orbitals. Each orbital can hold a maximum of two electrons (of opposite spin).

 Shell 1 Shell 2 Shell 3 Shell 4 Sub-Shell s s p s p d s p d f Number of orbitals in sub-shell 1 1 3 1 3 5 1 3 5 7 Number of electrons allowed in each orbital 2 2 2 2 2 2 2 2 2 2 Total number of electrons in each sub-shell 2 2 6 2 6 10 2 6 10 14

Concept behind s, p, d, f orbitals

Each shell is composed of one or more subshells, which are themselves composed of atomic orbitals. For example, the first (K) shell has one subshell, called 1s; the second (L) shell has two subshells, called 2s and 2p; the third shell has 3s, 3p, and 3d; the fourth shell has 4s, 4p, 4d and 4f; the fifth shell has 5s, 5p, 5d, and 5f and can theoretically hold more but the 5f subshell, although occupied in actinides, is not filled in any element occurring naturally. The various possible subshells are shown in the following table:

 Subshell label ? Max electrons Shells containing it Historical name s 0 2 Every shell sharp p 1 6 2nd shell and higher principal d 2 10 3rd shell and higher diffuse f 3 14 4th shell and higher fundamental g 4 18 5th shell and higher (theoretically) (next in alphabet after f)

## Number of electrons in each shell

Each subshell is constrained to hold 4? + 2 electrons at most, namely:

• Each s subshell holds at most 2 electrons
• Each p subshell holds at most 6 electrons
• Each d subshell holds at most 10 electrons
• Each f subshell holds at most 14 electrons
• Each g subshell holds at most 18 electrons

Therefore, the K shell, which contains only an s subshell, can hold up to 2 electrons; the L shell, which contains an s and a p, can hold up to 2 + 6 = 8 electrons, and so forth; that's why nth shell can hold up to 2n2 electrons.

 Shell name Subshell name Subshell max electrons Shell max electrons K 1s 2 2 L 2s 2 2 + 6 = 8 2p 6 M 3s 2 2 + 6 + 10 = 18 3p 6 3d 10 N 4s 2 2 + 6 + + 10 + 14 = 32 4p 6 4d 10 4f 14

Quantum chemistry is a branch of chemistry whose primary focus is the application of quantum mechanics in physical models and experiments of chemical systems. It involves heavy interplay of experimental and theoretical methods.

The quantum means, any physical entity (or amount)  that involves in  a reaction.

Quantum numbers are defined as a set of four numbers with the help of which we can get a complete information about all the electrons in an atom., i.e. there location, energy, type of orbitals occupied, shape and orientation of that orbitals etc.

In simple words, the quantum numbers describe an address or full description of the electrons.

These quantum numbers are of four types - principal, azimuthal, magnetic and spin quantum numbers.

Principal quantum number (n): It defines the main shell to which an electron belongs. The values of n =1,2,3,4,........

Azimuthal quantum number (l): It tells us the number of subshells present in the main shell and the orbital to which an electron belongs. Its value is equal to 0 to (n-1).

Magnetic quantum number (m): It informs the level of degeneracy of the orbitals. Its value is equal to -l, 0,+l.

Spin quantum number (s): It tells us whether the electron in an orbital is spinning in upward direction or downward direction. s has two values +1/2 for upward spin and -1/2 for downward spin.

Significance of Quantum numbers

(I) It rules out the existence of definite path of the electrons and other similar particles.

(II) The effect of HUP is significant only for motion of microscopic objects and negligible for that of microscopic object.

Regards

Topperlearning Team.
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