# Bohr model atom

To explain stability of the atom Niel Bohr a Danish physicst in 1913 proposed new model of atom.

The most important concept of this model of atom was that electron revolves only in certain fixed orbitsaround the nucleus without losing energy in the form of radiation.

Example: Solar system;

It appear some what like this,  Now here the sun is stationary at the centre while the planet revolves around it. But have you notice that planet always  revolves around the sun in fixed path. We never find any planet to jumping to different path all of sudden. They always encircle the sun  in definite path.

Similarly in the atomic structure , The nucleus act like a sun located at the centre and the electron like planets which revolves in a fixed, definite orbital. Those electron orbital are reoffered to as shell or energy levels.

Postulate:

• A atom consists of a small heavy positively charged nucleus in the centre and the electron revolves around the nucleus in a circular path called orbits.
• In a particular atom, the orbit in electron revolves are the discrete orbits, therefore also called shell energy levels. As energy of the orbits is fixed these are also called as stationary state. These are number as 1,2,3,4, etc. As we move outward from the nucleus or they are represented the letter K, L, M, N, etc. .  The energy of these shell increases as we move outward from the nucleus. Thus representing the energy of 1st  2nd 3rd 4thshell etc. By E1, E2, E3 E4, We have E1<E2>E3>E4 etc.
• However the gap between successive energy,  energy levels or shell around the nucleus.

• So long as on electron is revolves in a particular orbits. It can neither loss energy nor gain energy. Thus the atom is stable and does not collapse. This state of the atom with lowest energy is called ground state of atom.
• The energy lost or gained of electron only when it jumps one orbits to other . Energy lost or gained is equal to the difference of energy of the two energy levels evolved. Thus energy fall of an electron and it absorbs this energy  it will jump to some outer shell.
• The atom is then said to be in the excited state. In the excited state ,  the atom is not stable .  It loses or emits energy and jump back to some inner energy levels.

• Radius of bohr’s orbits = 0.0529n2/Z nm

(n= number of orbits, Z= atomic number)

• Energy of electron in bohr’s orbits, (En) = 2.18×10-18Z2/n2  in joule.

1) What is the concept of Bohr’s model of atom?

Answer: The most important concept of this model of atom was that electron revolves only in certain fixed orbits   around the nucleus without losing energy in the form of radiation.

2) Write the postulates of Bohr’s model of atom?

• Answer: A atom consists of a small heavy positively charged nucleus in the centre and the electron revolves around the nucleus in a circular path called orbits.
• In a particular atom, the orbit in electron revolves are the discrete orbits, therefore also called shell energy levels.  As energy of the orbits is fixed these are also called as stationary state. These are number as 1,2,3,4, etc. As we move outward from the nucleus or they are represented the letter K, L, M, N, etc. .  The energy of these shell increases as we move outward from the nucleus. Thus representing the energy of 1st  2nd 3rd 4th shell etc. By E1, E2, E3 E4, We have E1<E2>E3>E4 etc.

However the gap between successive energy ,  energy levels or shell around the nucleus.

• So long as on electron is revolves in a particular orbits. It can neither loss energy nor gain energy . Thus the atom is stable and does not collapse. This state of the atom with lowest energy is called ground state of atom.
• The energy lost or gained of electron only when it jumps one orbits to other . Energy lost or gained is equal to the difference of energy of the two energy levels evolved. Thus energy fall of an electron and it absorbs this energy  it will jump to some outer shell. The atom is then said to be in the excited state. In the excited state ,  the atom is not stable .  It loses or emits energy and jump back to some inner energy levels .
• Radius of bohr’s orbits = 0.0529n2/Z nm

( n= number of orbits, Z= atomic number)

• Energy of electron in bohr’s orbits, (En) = 2.18×10-18Z2/n2       in joule.