Weakest to Strongest :
intermolecular van der Waals electrostatic interaction :
intermolecular hydrogen bond :
intramolecular covalent bond :
intramolecular ionic bond :
Atomic orbitals are often represented as electrons spinning around the nucleus (top). However, orbital shells actually represent the volume in which the wave-form electron is most likely to be located (bottom). As such, orbitals are more akin to a cloud around the nucleus. The location of electrons within orbitals is described mathematically by the Schrödinger equations. Computer simulations reveal probability distributions for orbitals. Table of images of orbitals / Scatter plot of probabilities / interactive / virtual text / virtual text orbitals / download audio-anim of H2 bonding / audio-anim of hybridization of s p orbitals / voxel movie of orbital / movie 2 / movie 3 / movie 4 /
Ionic bonds are strong bonds formed when one atom is sufficiently electronegative to remove an electron from a sufficiently electropositive atom – creating negative and positive ions that are attracted by virtue of their opposite polarity.
When electrons are shared between two atoms of the same element, the electrons are shared equally, creating a non-polar covalent bond. When electrons are shared between atoms of different elements, the electrons are not shared equally, resulting in a polar covalent bond in which the increased-probability cloud over one atom has a slightly negative charge compared to a slightly positive charge over the other – a dipole (δ+, δ-).
Hydrogen bonds are intermolecular attractions between a hydrogen atom and a small, electronegative atom in a neighboring atom share a dipole-dipole attraction (δ+ δ-). Although stronger than most other intermolecular forces, a hydrogen bond is much weaker than either an ionic bond or a covalent bond. Within macromolecules such as proteins and nucleic acids, hydrogen bonds can exist between two parts of the same molecule and constrain the molecule's 3D shape.