Neutrons and protons in the structure of the nucleus


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The nucleus of an atom also has a structure ; the nucleus is composed of two different kind of particles, protons and neutrons.The fist evidence of the existence of the subatomic particles came from studies of the conduction of electricity through gases at low pressure.

Nucleus of atom:- A series of expermients carried out under direction of Ernest Rutherford in 1911 shaped the ideas about the nature of atom.He carried a gold foil experiment in which he bombarded this gold foil with alpha particles and with a fluorescent screen, they observed scattering of alpha particles.Most of the particles went  through the foil unchanged in direction;a few however, were reflected back at acute angles.By a mathemetical analysis,Rutherford showed that the scattering was caused by a small ,positively charged nucleus at the center of gold atom.Most of the the space of the atom is empty, due to which most particles passed through gold foil undeflected.

 The nucleus of an atom can be considered to consist of two different types of particles:

Proton : Is a nuclear particle having a positive charge equal to that of the electrons and a mass of more than 1800 times that of the electron.

Neutron: Is a nuclear particle having a mass almost identical to that of the proton but no electric charge.

Electrons are the negatively charged particles which are present outside the nucleus of the atom.

The number of protons in an atom is equal to its atomic number (z).

                              Z = number of protons.

The mass number of an atom,given the symbol A, is found by adding up the number of protons and neutrons in the neucleus. 

                       A = number of protons + number of neutrons

The number of neutrons in an atom is mass number minus number of protons.

               Number of neutrons = mass number - number of protons

The number of electrons in an atom is equal to the number of protons that is number of electrons in a neutral atom equal to its atomic number.

                 Number of electrons = number of protons.

Lets see an example:

The cobalt (Co ) has atomic number Z = 27 and it has 33 neutrons.How many protons and electrons it has?

 From the above discussion we know that Z = number of protons . So as atomic number is 27.

Number of protons in Co is = 27

And again from above we know that  Number of electrons = number of protons,

  so number of electrons in Co is = 27.

The atomic number of strontium (Sr) is 38 and mass number is 88 . Find its number of subatomic particle?

The subatomic particles are protons, neutrons and electrons.SO, we find them one by one:-

 As atomic number(Z) is 38  and from above discussion we know that number of protons equal to atomic number .So, number of protons are 38.

As number of neutrons are  mass number - number of protons .

 Number of neutrons = 80 - 38 =  50.

 And as  Number of electrons = number of protons

number of electrons = 38 .