Structure of an Atom

 

 

The modern model of an atom is based on the researches made mainly by Rutherford and Böhr.

 

According to this model,

 

Ø The atom consists of a positively charged core called the nucleus.

Ø Almost the entire mass of an atom is concentrated in its nucleus.

Ø The nucleus consists of protons and neutrons.

Ø The nucleus of hydrogen atom, however, consists of only one proton.

Ø In an atom, the nucleus is surrounded by electrons moving around it in certain fixed orbits.

Ø An atom as a whole is electrically neutral.

Ø The number of protons inside the nucleus of an atom is equal to the number of electrons surrounding the nucleus.

Ø Electrons, protons and neutrons are called the subatomic particles.

 

 

Model of an atom

 

 

Electron

Ø   The electron is a negatively charged subatomic particle.

Ø   The mass of an electron is about 1/1837 times that of a hydrogen atom. Thus, the mass of an electron is negligible.

Ø   The negative charge possessed by an electron is considered as one unit of negative charge.

 

Proton

Ø   The proton is a positively charged subatomic particle.

Ø   The mass of a proton is almost equal to that of a hydrogen atom. Thus, a proton is 1837 times heavier than an electron.

Ø   The positive charge possessed by a proton is considered as one unit of positive charge.

 

 

Neutron

Ø   The neutron is a subatomic particle which does not carry any electrical charge.

Ø   The mass of a neutron is almost equal to that of a proton.

Ø   The mass of a neutron is taken as one atomic mass unit (or 1 amu or 1 u), where 1 u = 1.66 × 10^–24 g.

Ø   The symbol for atomic mass unit is u.