Problem 86 - Chemistry Central Science

Question

Nearly all the mass of an atom is in the nucleus, which has a very small radius. When atoms bond together (for example, two fluorine atoms in \(\mathrm{F}_{2}\) ), why is the distance separating the nuclei so much larger than the radii of the nuclei?

Step-by-Step Solution

Answer

The distance between the nuclei of two bonded atoms, such as two fluorine atoms in F₂, is much larger than the radii of the individual nuclei because the bond length is determined by the balance between attractive and repulsive forces. While the attractive forces from sharing electrons promote bonding, repulsive forces between the positively charged nuclei prevent the atoms from getting too close. The bond length represents the equilibrium distance at which the potential energy of the system is minimized, which is considerably larger than the radii of the nuclei.

Step 1: Understand the structure of an atom

Atoms are comprised of a central region called the nucleus (containing protons and neutrons) and surrounding regions containing electrons. The mass of an atom is mostly concentrated in the nucleus, which is very small in size. The electrons occupy various energy levels, or orbitals, around the nucleus.

Step 2: Understand atomic bonding

Atoms bond together to form molecules through interactions between their electrons. In the case of F₂, two fluorine atoms bond together through a covalent bond, where they share a pair of electrons. The bond is a result of the electrostatic attraction between the positively charged nuclei of the two atoms and the negatively charged shared electrons.

Step 3: Consider repulsive forces between nuclei

The nuclei of two atoms have positive charges due to the protons they contain. As a result, they experience repulsive forces from one another according to Coulomb's law. When two atoms come close to each other, their nuclei start to repel each other, making it energetically unfavorable for them to get too close.

Step 4: Understand the bond length

The bond length is defined as the equilibrium distance between the nuclei of two bonded atoms. At this distance, the attractive forces between the two nuclei and the shared electrons balance the repulsive forces between the nuclei. Thus, the bond length is determined by the minimum in the potential energy of the system.

Step 5: Relate bond length to the radii of nuclei

While the nuclei of the atoms are indeed very small, the key factor in determining the atomic bond length is the balance between attractive and repulsive forces. Since the repulsive forces between the positively charged nuclei increase as the nuclei get closer, they prevent the bond length from being as small as the radii of the nuclei. The bond length, which is considerably larger than the radii of the nuclei, represents the equilibrium distance between the two nuclei at which the potential energy of the system is minimized.