repulsion

Examples of repulsion in the following topics:

• Ethane Conformations

  • As a result of bond-electron repulsions, illustrated on the right above, the eclipsed conformation is less stable than the staggered conformation by roughly 3 kcal / mol (eclipsing strain).
  • The most severe repulsions in the eclipsed conformation are depicted by the red arrows.
  • There are six other less strong repulsions that are not shown.
  • In the staggered conformation there are six equal bond repulsions, four of which are shown by the blue arrows, and these are all substantially less severe than the three strongest eclipsed repulsions.
  • Although steric and/or bond electron repulsion remain the most popular explanation for the hindered rotation of ethane, molecular orbital interactions have also been proposed as a significant factor.

• Steric Effects

  • As the atoms near each other, their outer (valence) electrons interact to repel each other, and this repulsion energy increases very rapidly as the distance r decreases.
  • Consequently, as the two atoms come together, an initial attraction becomes a strong repulsion, as shown by the dark blue curve.
  • This increase in energy as atoms are crowded together is called steric repulsion or steric hindrance.

• Atomic Size

  • an increase in atomic size because of additional repulsions between electrons,
  • no effect at all as the two opposing tendencies of electron repulsion and nuclear attraction balance each other out.
  • Experiments have shown that the first case is what happens: the increase in nuclear charge overcomes the repulsion between the additional electrons in the valence level.

• Nuclear Fusion

  • This force, called the strong nuclear force, overcomes electric repulsion in a very close range.
  • At large distances, two nuclei repel one another because of the repulsive electrostatic force between their positively charged protons.
  • If two nuclei can be brought close enough together, however, the electrostatic repulsion can be overcome by the attractive nuclear force, which is stronger at close distances.
  • The electrostatic force, on the other hand, is dependent upon the inverse-square of the distance between two like-charged particles, so a proton added to a nucleus will feel an electrostatic repulsion from all the other protons in the nucleus.
  • At nucleus radii distances, the attractive nuclear force is stronger than the repulsive electrostatic force.

• Table of Geometries

  • The valence shell electron pair repulsion (VSEPR) model focuses on the bonding and nonbonding electron pairs present in the outermost (valence) shell of an atom that connects with two or more other atoms.
  • The orbitals containing the various bonding and non-bonding pairs in the valence shell will extend out from the central atom in directions that minimize their mutual repulsions.

• Introduction to Intermolecular Forces

  • It should be noted that there are also smaller repulsive forces between molecules that increase rapidly at very small intermolecular distances.

• Applying the VSEPR Model

  • The valence shell electron pair repulsion (VSEPR) model predicts the shape of individual molecules based on the extent of electron-pair electrostatic repulsion.
  • According to VSEPR, the valence electron pairs surrounding an atom mutually repel each other; they adopt an arrangement that minimizes this repulsion, thus determining the molecular geometry.
  • Because a nonbonding orbital has no atomic nucleus at its far end to draw the electron cloud toward it, the charge will be concentrated closer to the central atom; therefore, nonbonding orbitals exert more repulsion on other orbitals than do bonding orbitals.
  • The repulsion between these will be at a minimum when the angle between any two is 120°.

• Tetrahedral and Square Planar Complexes

  • The dx2−dy2 and dz2 orbitals should be equally low in energy because they exist between the ligand axis, allowing them to experience little repulsion.
  • This maximizes repulsion and raises energy levels.

• Lone Electron Pairs

  • The orbitals containing the various bonding and nonbonding pairs in the valence shell will extend out from the central atom in directions that minimize their mutual repulsions.
  • Because a nonbonding orbital has no atomic nucleus at its far end to draw the electron cloud toward it, the charge in such an orbital will be concentrated closer to the central atom; as a consequence, nonbonding orbitals exert more repulsion on other orbitals than do bonding orbitals.

• Nuclear Stability

  • This is because, for any constant number of protons, the difference between nuclear force and electrostatic repulsion of protons increases with increasing neutron count.