Covalent bonds occur when atoms share electrons; however, becasue different atoms have different electronegativites, there is often an uneven distribution of electrons between the two that are covalently bonded. This results in polarity, where one atom is slightly positive, while the other atom is slightly negative. This can lead to interactions with other molecules that result in non-covalent bonds. Non-covalent bonds are electrostatic. This does not mean that they are only between fully charged molecules. Non-covalent bonds occur when two molecules have any sort of charge: partial or full or temporary or permanent. They can be intermolecular or intramolecular, meaning two parts of one molecule interact with each other. Noncovalent bonds are classified based on their magnitude and duration. Ionic bonds occur between opposite permanent, full charges. Meanwhile, van der Waals interactions occue between opposite temporary, partial charges. Dipole interactions describe any non-covalent bond in between. Dipole interactions can be dipole-dipole, ion-dipole, etc. A very important dipole-dipole interaction is the hydrogen bond. A hydrogen bond occurs when it is bound to a highly electronegative atom, usually nitrogen or oxygen. This causes the hydrogen atom to hold a permanent, partially positive charge. When it interacts with an atom with a permanent, partially negative charge, it forms a hydrogen bond.
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