<< Chapter < Page Chapter >> Page >

To hold positively charged protons together in the very small volume of a nucleus requires very strong attractive forces because the positively charged protons repel one another strongly at such short distances. The force of attraction that holds the nucleus together is the strong nuclear force    . (The strong force is one of the four fundamental forces that are known to exist. The others are the electromagnetic force, the gravitational force, and the nuclear weak force.) This force acts between protons, between neutrons, and between protons and neutrons. It is very different from the electrostatic force that holds negatively charged electrons around a positively charged nucleus (the attraction between opposite charges). Over distances less than 10 −15 meters and within the nucleus, the strong nuclear force is much stronger than electrostatic repulsions between protons; over larger distances and outside the nucleus, it is essentially nonexistent.

Nuclear binding energy

As a simple example of the energy associated with the strong nuclear force, consider the helium atom composed of two protons, two neutrons, and two electrons. The total mass of these six subatomic particles may be calculated as:

( 2 × 1.0073 amu ) + ( 2 × 1.0087 amu ) + ( 2 × 0.00055 amu ) = 4.0331 amu protons neutrons electrons

However, mass spectrometric measurements reveal that the mass of an 2 4 He atom is 4.0026 amu, less than the combined masses of its six constituent subatomic particles. This difference between the calculated and experimentally measured masses is known as the mass defect    of the atom. In the case of helium, the mass defect indicates a “loss” in mass of 4.0331 amu – 4.0026 amu = 0.0305 amu. The loss in mass accompanying the formation of an atom from protons, neutrons, and electrons is due to the conversion of that mass into energy that is evolved as the atom forms. The nuclear binding energy    is the energy produced when the atoms’ nucleons are bound together; this is also the energy needed to break a nucleus into its constituent protons and neutrons. In comparison to chemical bond energies, nuclear binding energies are vastly greater, as we will learn in this section. Consequently, the energy changes associated with nuclear reactions are vastly greater than are those for chemical reactions.

The conversion between mass and energy is most identifiably represented by the mass-energy equivalence equation    as stated by Albert Einstein:

E = m c 2

where E is energy, m is mass of the matter being converted, and c is the speed of light in a vacuum. This equation can be used to find the amount of energy that results when matter is converted into energy. Using this mass-energy equivalence equation, the nuclear binding energy of a nucleus may be calculated from its mass defect, as demonstrated in [link] . A variety of units are commonly used for nuclear binding energies, including electron volts (eV) , with 1 eV equaling the amount of energy necessary to the move the charge of an electron across an electric potential difference of 1 volt, making 1 eV = 1.602 × 10 –19 J.

Questions & Answers

so from dis concept rust x an atom
quame Reply
compare the dual nature of light
Eddie Reply
list 10 gases and their IUPAC name
Ogweimoh Reply
what are the likely questions for jamb
richez Reply
in group atomic number?
Dolly Reply
why is contact process important?
Kolawole Reply
what structure?
Musa Reply
of the above question.
Draw the Lewis structure of the following : Nitrate anion Nitrogen dioxide
Nakyanzi Reply
a first order reaction is 40% complete after 8 minutes how long will it be before it is 95% complete
IKO Reply
plea what are the best topics in chemistry to know
Sandra Reply
atomic theory . nuclear chemistry . chemical reaction. chemical equilibrium . organic chemistry. molecules concept 1 n 2. kinetic theory of gases.
wat topics are the most important in biology
cells 1 n 2, ecology. insects. genetics. plants. nutrition.
organic chemistry
Explain the Factors which Affect Ionisation Energy
Nakyanzi Reply
Screening effect of shell, distances of electron from it nucleus, numbers of electron
Thanks dear
how does the periodic table looks like
Blessing Reply
name process taking place when crystals of zinc nitrate change into solution when exposed to air
Jeniffer Reply
why boiling point of propane-l-ol is higher than of propane
I want to more about chemistry. please guys teach me
Moses Reply
on which topic do you want more enlightenment?
guys what is atomic number
atomic number represents the number of electrons in an atom
On which topic Mr. poster
the periodic table , can I have the table pls
Obasi Reply
yes me too
how does this discussion work

Get the best Chemistry course in your pocket!

Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Chemistry' conversation and receive update notifications?