<P> The hydrogen nucleus contain just one proton , Its isotope deuterium , or heavy hydrogen , contains a proton and a neutron . Helium contains two protons and two neutrons , and carbon , nitrogen and oxygen - six , seven and eight of each particle , respectively . However , a helium nucleus weighs less than the sum of the weights of the two hydrogen nuclei which combine to make it . The same is true for carbon , nitrogen and oxygen . For example , the carbon nucleus is slightly lighter than three helium nuclei , which can combine to make a carbon nucleus . This difference is known as the mass defect . </P>
<P> The hydrogen nucleus contain just one proton , Its isotope deuterium , or heavy hydrogen , contains a proton and a neutron . Helium contains two protons and two neutrons , and carbon , nitrogen and oxygen - six , seven and eight of each particle , respectively . However , a helium nucleus weighs less than the sum of the weights of the two hydrogen nuclei which combine to make it . The same is true for carbon , nitrogen and oxygen . For example , the carbon nucleus is slightly lighter than three helium nuclei , which can combine to make a carbon nucleus . This difference is known as the mass defect . </P>
why is the total mass of a helium nucleus not equal to the mass of its individual parts
why is the total mass of a helium nucleus not equal to the mass of its individual parts
mass defect
mass defect