In the following molecule \(\mathrm{AB}\), one of the atoms is more electronegative than the other. Which is more electronegative, and how do you know? \(\delta-\delta+\) \(\mathrm{A}-\mathrm{B}\)

Chemical bonding is the force that holds atoms together in molecules and compounds. It is a lasting attraction between atoms, ions, or molecules that allows the formation of chemical compounds. There are three primary types of chemical bonds: ionic, covalent, and metallic. In ionic bonding, atoms transfer electrons to each other, typically between a metal and a nonmetal, which creates ions. Ions are charged particles where one atom loses electrons and becomes a positively charged cation, while the other atom gains electrons to become a negatively charged anion.

Covalent bonding, on the other hand, involves the sharing of electron pairs between atoms. These shared electrons glue two or more atoms together to stabilize them. In pure covalent bonds, atoms share the electrons equally. However, when atoms have different electronegativities, the sharing is unequal, leading to polar covalent bonds. Metallic bonding, which occurs between metals, involves a 'sea' of delocalized electrons surrounding a lattice of metal cations. Understanding the type of bond and the properties of the elements involved is crucial in predicting the behavior of compounds and their reactivity.

Polar bonds are a type of covalent bond where electrons are shared unequally between atoms with different electronegativities. Electronegativity is an atom's ability to attract shared electrons in a bond. The result of this uneven sharing is that one atom becomes slightly negatively charged (represented by δ−), while the other atom becomes slightly positively charged (represented by δ+).

This slight charge creates a dipole moment, where there's a separation of charge within the bond. These dipoles within molecules can influence physical properties like boiling point, melting point, and solubility. For example, water (H₂O) is a classical example of a molecule with polar bonds, as oxygen is more electronegative than hydrogen, resulting in a strong dipole moment. This polarity allows water to form hydrogen bonds with other water molecules or dissolve various other substances, which is why it's often called the 'universal solvent'.

Partial charges arise in polar covalent bonds and are indicated by the symbols δ+ and δ-. They are not full charges as seen in ionic compounds but indicate a lower level of charge due to unequal sharing of electrons. The presence of partial charges is essential for the concept of electronegativity since they signify which atom attracts electrons more strongly.

The more electronegative atom will have a higher electron density and thus will carry a partial negative charge (δ-). The less electronegative atom, with a lower electron density, will have a partial positive charge (δ+). It's these partial charges that give rise to many of the interesting properties of molecules, such as their ability to interact with other molecules of similar or different charges. The effect of partial charges is most pronounced in solutions and biological systems, where it influences the interaction between molecules, such as in the binding of substrates to enzymes or the formation of cell membranes.